Methamphetamine [note 1] (contracted from N-methylamphetamine) is a potent central nervous system (CNS) stimulant that is mainly used as a recreational or performance-enhancing drug and less commonly as a second-line treatment for attention deficit hyperactivity disorder (ADHD). [23] It has also been researched as a potential treatment for traumatic brain injury. [7] Methamphetamine was discovered in 1893 and exists as two enantiomers: levo-methamphetamine and dextro-methamphetamine. [note 2] Methamphetamine properly refers to a specific chemical substance, the racemic free base, which is an equal mixture of levomethamphetamine and dextromethamphetamine in their pure amine forms, but the hydrochloride salt, commonly called crystal meth, is widely used. Methamphetamine is rarely prescribed over concerns involving its potential for recreational use as an aphrodisiac and euphoriant, among other concerns, as well as the availability of safer substitute drugs with comparable treatment efficacy such as Adderall and Vyvanse. [23] While pharmaceutical formulations of methamphetamine in the United States are labeled as methamphetamine hydrochloride, they contain dextromethamphetamine as the active ingredient. [23] [note 3] Dextromethamphetamine is a stronger CNS stimulant than levomethamphetamine. [23]
Both racemic methamphetamine and dextromethamphetamine are illicitly trafficked and sold owing to their potential for recreational use. The highest prevalence of illegal methamphetamine use occurs in parts of Asia and Oceania, and in the United States, where racemic methamphetamine and dextromethamphetamine are classified as Schedule II controlled substances. Levomethamphetamine is available as an over-the-counter (OTC) drug for use as an inhaled nasal decongestant in the United States. [note 4] Internationally, the production, distribution, sale, and possession of methamphetamine is restricted or banned in many countries, owing to its placement in schedule II of the United Nations Convention on Psychotropic Substances treaty. While dextromethamphetamine is a more potent drug, racemic methamphetamine is illicitly produced more often, owing to the relative ease of synthesis and regulatory limits of chemical precursor availability.
In low to moderate doses, methamphetamine can elevate mood, increase alertness, concentration and energy in fatigued individuals, reduce appetite, and promote weight loss. At very high doses, it can induce psychosis, breakdown of skeletal muscle, seizures, and bleeding in the brain. Chronic high-dose use can precipitate unpredictable and rapid mood swings, stimulant psychosis (e.g., paranoia, hallucinations, delirium, and delusions), and violent behavior. Recreationally, methamphetamine's ability to increase energy has been reported to lift mood and increase sexual desire to such an extent that users are able to engage in sexual activity continuously for several days while binging the drug. [28] Methamphetamine is known to possess a high addiction liability (i.e., a high likelihood that long-term or high dose use will lead to compulsive drug use) and high dependence liability (i.e., a high likelihood that withdrawal symptoms will occur when methamphetamine use ceases). Discontinuing methamphetamine after heavy use may lead to a post-acute-withdrawal syndrome, which can persist for months beyond the typical withdrawal period. At high doses, methamphetamine is neurotoxic to human midbrain dopaminergic neurons and, to a lesser extent, serotonergic neurons. [29] [30] Methamphetamine neurotoxicity causes adverse changes in brain structure and function, such as reductions in grey matter volume in several brain regions, as well as adverse changes in markers of metabolic integrity. [30]
Methamphetamine belongs to the substituted phenethylamine and substituted amphetamine chemical classes. It is related to the other dimethylphenethylamines as a positional isomer of these compounds, which share the common chemical formula C 10 H 15 N .
In the United States, methamphetamine hydrochloride, sold under the brand name Desoxyn, is FDA-approved for the treatment of attention deficit hyperactivity disorder (ADHD); [25] [31] however, the FDA notes that the limited therapeutic usefulness of methamphetamine should be weighed against the risks associated with its use. [25] To avoid toxicity and risk of side effects, FDA guidelines recommend an initial dose of methamphetamine at doses 5–10 mg/day for ADHD in adults and children over six years of age, and may be increased at weekly intervals of 5 mg, up to 25 mg/day, until optimum clinical response is found; the usual effective dose is around 20–25 mg/day. [23] [7] [25] Methamphetamine is sometimes prescribed off-label for obesity, narcolepsy, and idiopathic hypersomnia. [23] [32] [33] In the United States, methamphetamine's levorotary form is available in some over-the-counter (OTC) nasal decongestant products. [23] [note 4]
Although the pharmaceutical name "methamphetamine hydrochloride" may suggest a racemic mixture, Desoxyn contains enantiopure dextromethamphetamine, which is a more potent stimulant than both levomethamphetamine and racemic methamphetamine. [23] [note 3] This naming convention deviates from the standard practice observed with other stimulants, such as Adderall and dextroamphetamine, where the dextrorotary enantiomer is explicitly identified as an active ingredient in both generic and brand-name pharmaceuticals. [34] [35] [36]
As methamphetamine is associated with a high potential for misuse, the drug is regulated under the Controlled Substances Act and is listed under Schedule II in the United States. [3] Methamphetamine hydrochloride dispensed in the United States is required to include a boxed warning regarding its potential for recreational misuse and addiction liability. [25]
Desoxyn and Desoxyn Gradumet are both pharmaceutical forms of the drug. The latter is no longer produced and is a extended-release form of the drug, flattening the curve of the effect of the drug while extending it. [37]
Methamphetamine is often used recreationally for its effects as a potent euphoriant and stimulant as well as aphrodisiac qualities. [38]
According to a National Geographic TV documentary on methamphetamine, an entire subculture known as party and play is based around sexual activity and methamphetamine use. [38] Participants in this subculture, which consists almost entirely of homosexual male methamphetamine users, will typically meet up through internet dating sites and have sex. [38] Because of its strong stimulant and aphrodisiac effects and inhibitory effect on ejaculation, with repeated use, these sexual encounters will sometimes occur continuously for several days on end. [38] The crash following the use of methamphetamine in this manner is very often severe, with marked hypersomnia (excessive daytime sleepiness). [38] The party and play subculture is prevalent in major US cities such as San Francisco and New York City. [38] [39]
Methamphetamine is contraindicated in individuals with a history of substance use disorder, heart disease, or severe agitation or anxiety, or in individuals currently experiencing arteriosclerosis, glaucoma, hyperthyroidism, or severe hypertension. [25] The FDA states that individuals who have experienced hypersensitivity reactions to other stimulants in the past or are currently taking monoamine oxidase inhibitors should not take methamphetamine. [25] The FDA also advises individuals with bipolar disorder, depression, elevated blood pressure, liver or kidney problems, mania, psychosis, Raynaud's phenomenon, seizures, thyroid problems, tics, or Tourette syndrome to monitor their symptoms while taking methamphetamine. [25] Owing to the potential for stunted growth, the FDA advises monitoring the height and weight of growing children and adolescents during treatment. [25]
Methamphetamine is a sympathomimetic drug that causes vasoconstriction and tachycardia. Methamphetamine also promotes abnormal extra heart beats and irregular heart rhythms some of which may be life threatening. [41]
The effects can also include loss of appetite, hyperactivity, dilated pupils, flushed skin, excessive sweating, increased movement, dry mouth and teeth grinding (potentially leading to condition informally known as meth mouth ), headache, rapid breathing, high body temperature, diarrhea, constipation, blurred vision, dizziness, twitching, numbness, tremors, dry skin, acne, and pale appearance. [25] [42] Long-term meth users may have sores on their skin; [43] [44] these may be caused by scratching due to itchiness or the belief that insects are crawling under their skin, [43] and the damage is compounded by poor diet and hygiene. [44] Numerous deaths related to methamphetamine overdoses have been reported. [45] [46] Additionally, "[p]ostmortem examinations of human tissues have linked use of the drug to diseases associated with aging, such as coronary atherosclerosis and pulmonary fibrosis", [47] which may be caused "by a considerable rise in the formation of ceramides, pro-inflammatory molecules that can foster cell aging and death." [47]
Methamphetamine users, particularly heavy users, may lose their teeth abnormally quickly, regardless of the route of administration, from a condition informally known as meth mouth. [48] The condition is generally most severe in users who inject the drug, rather than swallow, smoke, or inhale it. [48] According to the American Dental Association, meth mouth "is probably caused by a combination of drug-induced psychological and physiological changes resulting in xerostomia (dry mouth), extended periods of poor oral hygiene, frequent consumption of high-calorie, carbonated beverages and bruxism (teeth grinding and clenching)". [48] [49] As dry mouth is also a common side effect of other stimulants, which are not known to contribute severe tooth decay, many researchers suggest that methamphetamine-associated tooth decay is more due to users' other choices. They suggest the side effect has been exaggerated and stylized to create a stereotype of current users as a deterrence for new ones. [31]
Methamphetamine use was found to be related to higher frequencies of unprotected sexual intercourse in both HIV-positive and unknown casual partners, an association more pronounced in HIV-positive participants. [50] These findings suggest that methamphetamine use and engagement in unprotected anal intercourse are co-occurring risk behaviors, behaviors that potentially heighten the risk of HIV transmission among gay and bisexual men. [50] Methamphetamine use allows users of both sexes to engage in prolonged sexual activity, which may cause genital sores and abrasions as well as priapism in men. [25] [51] Methamphetamine may also cause sores and abrasions in the mouth via bruxism, increasing the risk of sexually transmitted infection. [25] [51]
Besides the sexual transmission of HIV, it may also be transmitted between users who share a common needle. [52] The level of needle sharing among methamphetamine users is similar to that among other drug injection users. [52]
The psychological effects of methamphetamine can include euphoria, dysphoria, changes in libido, alertness, apprehension and concentration, decreased sense of fatigue, insomnia or wakefulness, self-confidence, sociability, irritability, restlessness, grandiosity and repetitive and obsessive behaviors. [25] [42] [53] Peculiar to methamphetamine and related stimulants is "punding", persistent non-goal-directed repetitive activity. [54] Methamphetamine use also has a high association with anxiety, depression, amphetamine psychosis, suicide, and violent behaviors. [55] [56]
Methamphetamine is directly neurotoxic to dopaminergic neurons in both lab animals and humans. [29] [30] Excitotoxicity, oxidative stress, metabolic compromise, UPS dysfunction, protein nitration, endoplasmic reticulum stress, p53 expression and other processes contributed to this neurotoxicity. [29] [60] [4] In line with its dopaminergic neurotoxicity, methamphetamine use is associated with a higher risk of Parkinson's disease. [61] In addition to its dopaminergic neurotoxicity, a review of evidence in humans indicated that high-dose methamphetamine use can also be neurotoxic to serotonergic neurons. [30] It has been demonstrated that a high core temperature is correlated with an increase in the neurotoxic effects of methamphetamine. [62] Withdrawal of methamphetamine in dependent persons may lead to post-acute withdrawal which persists months beyond the typical withdrawal period. [4]
Magnetic resonance imaging studies on human methamphetamine users have also found evidence of neurodegeneration, or adverse neuroplastic changes in brain structure and function. [30] In particular, methamphetamine appears to cause hyperintensity and hypertrophy of white matter, marked shrinkage of hippocampi, and reduced gray matter in the cingulate cortex, limbic cortex, and paralimbic cortex in recreational methamphetamine users. [30] Moreover, evidence suggests that adverse changes in the level of biomarkers of metabolic integrity and synthesis occur in recreational users, such as a reduction in N-acetylaspartate and creatine levels and elevated levels of choline and myoinositol. [30]
Methamphetamine has been shown to activate TAAR1 in human astrocytes and generate cAMP as a result. [61] Activation of astrocyte-localized TAAR1 appears to function as a mechanism by which methamphetamine attenuates membrane-bound EAAT2 (SLC1A2) levels and function in these cells. [61]
Methamphetamine binds to and activates both sigma receptor subtypes, σ1 and σ2, with micromolar affinity. [59] [63] Sigma receptor activation may promote methamphetamine-induced neurotoxicity by facilitating hyperthermia, increasing dopamine synthesis and release, influencing microglial activation, and modulating apoptotic signaling cascades and the formation of reactive oxygen species. [59] [63]
Addiction and dependence glossary [64] [65] [66] | |
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Current models of addiction from chronic drug use involve alterations in gene expression in certain parts of the brain, particularly the nucleus accumbens. [74] [75] The most important transcription factors [note 5] that produce these alterations are ΔFosB, cAMP response element binding protein (CREB), and nuclear factor kappa B (NFκB). [75] ΔFosB plays a crucial role in the development of drug addictions, since its overexpression in D1-type medium spiny neurons in the nucleus accumbens is necessary and sufficient [note 6] for most of the behavioral and neural adaptations that arise from addiction. [65] [75] [77] Once ΔFosB is sufficiently overexpressed, it induces an addictive state that becomes increasingly more severe with further increases in ΔFosB expression. [65] [77] It has been implicated in addictions to alcohol, cannabinoids, cocaine, methylphenidate, nicotine, opioids, phencyclidine, propofol, and substituted amphetamines, among others. [75] [77] [78] [79] [80]
ΔJunD, a transcription factor, and G9a, a histone methyltransferase enzyme, both directly oppose the induction of ΔFosB in the nucleus accumbens (i.e., they oppose increases in its expression). [65] [75] [81] Sufficiently overexpressing ΔJunD in the nucleus accumbens with viral vectors can completely block many of the neural and behavioral alterations seen in chronic drug use (i.e., the alterations mediated by ΔFosB). [75] ΔFosB also plays an important role in regulating behavioral responses to natural rewards, such as palatable food, sex, and exercise. [75] [78] [82] Since both natural rewards and addictive drugs induce expression of ΔFosB (i.e., they cause the brain to produce more of it), chronic acquisition of these rewards can result in a similar pathological state of addiction. [75] [78] ΔFosB is the most significant factor involved in both amphetamine addiction and amphetamine-induced sex addictions, which are compulsive sexual behaviors that result from excessive sexual activity and amphetamine use. [note 7] [78] [83] These sex addictions (i.e., drug-induced compulsive sexual behaviors) are associated with a dopamine dysregulation syndrome which occurs in some patients taking dopaminergic drugs, such as amphetamine or methamphetamine. [78] [82] [83]
Methamphetamine addiction is persistent for many individuals, with 61% of individuals treated for addiction relapsing within one year. [84] About half of those with methamphetamine addiction continue with use over a ten-year period, while the other half reduce use starting at about one to four years after initial use. [85]
The frequent persistence of addiction suggests that long-lasting changes in gene expression may occur in particular regions of the brain, and may contribute importantly to the addiction phenotype. In 2014, a crucial role was found for epigenetic mechanisms in driving lasting changes in gene expression in the brain. [81]
A review in 2015 [86] summarized a number of studies involving chronic methamphetamine use in rodents. Epigenetic alterations were observed in the brain reward pathways, including areas like ventral tegmental area, nucleus accumbens, and dorsal striatum, the hippocampus, and the prefrontal cortex. Chronic methamphetamine use caused gene-specific histone acetylations, deacetylations and methylations. Gene-specific DNA methylations in particular regions of the brain were also observed. The various epigenetic alterations caused downregulations or upregulations of specific genes important in addiction. For instance, chronic methamphetamine use caused methylation of the lysine in position 4 of histone 3 located at the promoters of the c-fos and the C-C chemokine receptor 2 (ccr2) genes, activating those genes in the nucleus accumbens (NAc). [86] c-fos is well known to be important in addiction. [87] The ccr2 gene is also important in addiction, since mutational inactivation of this gene impairs addiction. [86]
In methamphetamine addicted rats, epigenetic regulation through reduced acetylation of histones, in brain striatal neurons, caused reduced transcription of glutamate receptors. [88] Glutamate receptors play an important role in regulating the reinforcing effects of addictive drugs. [89]
Administration of methamphetamine to rodents causes DNA damage in their brain, particularly in the nucleus accumbens region. [90] [91] During repair of such DNA damages, persistent chromatin alterations may occur such as in the methylation of DNA or the acetylation or methylation of histones at the sites of repair. [92] These alterations can be epigenetic scars in the chromatin that contribute to the persistent epigenetic changes found in methamphetamine addiction.
A 2018 systematic review and network meta-analysis of 50 trials involving 12 different psychosocial interventions for amphetamine, methamphetamine, or cocaine addiction found that combination therapy with both contingency management and community reinforcement approach had the highest efficacy (i.e., abstinence rate) and acceptability (i.e., lowest dropout rate). [93] Other treatment modalities examined in the analysis included monotherapy with contingency management or community reinforcement approach, cognitive behavioral therapy, 12-step programs, non-contingent reward-based therapies, psychodynamic therapy, and other combination therapies involving these. [93]
As of December 2019 [update] , there is no effective pharmacotherapy for methamphetamine addiction. [94] [95] [96] A systematic review and meta-analysis from 2019 assessed the efficacy of 17 different pharmacotherapies used in randomized controlled trials (RCTs) for amphetamine and methamphetamine addiction; [95] it found only low-strength evidence that methylphenidate might reduce amphetamine or methamphetamine self-administration. [95] There was low- to moderate-strength evidence of no benefit for most of the other medications used in RCTs, which included antidepressants (bupropion, mirtazapine, sertraline), antipsychotics (aripiprazole), anticonvulsants (topiramate, baclofen, gabapentin), naltrexone, varenicline, citicoline, ondansetron, prometa, riluzole, atomoxetine, dextroamphetamine, and modafinil. [95] [ verification needed ]
Tolerance is expected to develop with regular methamphetamine use and, when used recreationally, this tolerance develops rapidly. [97] [98] In dependent users, withdrawal symptoms are positively correlated with the level of drug tolerance. [99] Depression from methamphetamine withdrawal lasts longer and is more severe than that of cocaine withdrawal. [100]
According to the current Cochrane review on drug dependence and withdrawal in recreational users of methamphetamine, "when chronic heavy users abruptly discontinue [methamphetamine] use, many report a time-limited withdrawal syndrome that occurs within 24 hours of their last dose". [99] Withdrawal symptoms in chronic, high-dose users are frequent, occurring in up to 87.6% of cases, and persist for three to four weeks with a marked "crash" phase occurring during the first week. [99] Methamphetamine withdrawal symptoms can include anxiety, drug craving, dysphoric mood, fatigue, increased appetite, increased movement or decreased movement, lack of motivation, sleeplessness or sleepiness, and vivid or lucid dreams. [99]
Methamphetamine that is present in a mother's bloodstream can pass through the placenta to a fetus and be secreted into breast milk. [100] Infants born to methamphetamine-abusing mothers may experience a neonatal withdrawal syndrome, with symptoms involving of abnormal sleep patterns, poor feeding, tremors, and hypertonia. [100] This withdrawal syndrome is relatively mild and only requires medical intervention in approximately 4% of cases. [100]
Form of neuroplasticity or behavioral plasticity | Type of reinforcer | Sources | |||||
---|---|---|---|---|---|---|---|
Opiates | Psychostimulants | High fat or sugar food | Sexual intercourse | Physical exercise (aerobic) | Environmental enrichment | ||
ΔFosB expression in nucleus accumbens D1-type MSNs | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | [78] |
Behavioral plasticity | |||||||
Escalation of intake | Yes | Yes | Yes | [78] | |||
Psychostimulant cross-sensitization | Yes | Not applicable | Yes | Yes | Attenuated | Attenuated | [78] |
Psychostimulant self-administration | ↑ | ↑ | ↓ | ↓ | ↓ | [78] | |
Psychostimulant conditioned place preference | ↑ | ↑ | ↓ | ↑ | ↓ | ↑ | [78] |
Reinstatement of drug-seeking behavior | ↑ | ↑ | ↓ | ↓ | [78] | ||
Neurochemical plasticity | |||||||
CREB phosphorylation in the nucleus accumbens | ↓ | ↓ | ↓ | ↓ | ↓ | [78] | |
Sensitized dopamine response in the nucleus accumbens | No | Yes | No | Yes | [78] | ||
Altered striatal dopamine signaling | ↓DRD2, ↑DRD3 | ↑DRD1, ↓DRD2, ↑DRD3 | ↑DRD1, ↓DRD2, ↑DRD3 | ↑DRD2 | ↑DRD2 | [78] | |
Altered striatal opioid signaling | No change or ↑μ-opioid receptors | ↑μ-opioid receptors ↑κ-opioid receptors | ↑μ-opioid receptors | ↑μ-opioid receptors | No change | No change | [78] |
Changes in striatal opioid peptides | ↑dynorphin No change: enkephalin | ↑dynorphin | ↓enkephalin | ↑dynorphin | ↑dynorphin | [78] | |
Mesocorticolimbic synaptic plasticity | |||||||
Number of dendrites in the nucleus accumbens | ↓ | ↑ | ↑ | [78] | |||
Dendritic spine density in the nucleus accumbens | ↓ | ↑ | ↑ | [78] |
Unlike other drugs, babies with prenatal exposure to methamphetamine do not show immediate signs of withdrawal. Instead, cognitive and behavioral problems start emerging when the children reach school age. [101]
A prospective cohort study of 330 children showed that at the age of 3, children with methamphetamine exposure showed increased emotional reactivity, as well as more signs of anxiety and depression; and at the age of 5, children showed higher rates of externalizing disorders and attention deficit hyperactivity disorder (ADHD). [102]
Methamphetamine overdose is a diverse term. It frequently refers to the exaggeration of the unusual effects with features such as irritability, agitation, hallucinations and paranoia. [5] [25] The cardiovascular effects are typically not noticed in young healthy people. Hypertension and tachycardia are not apparent unless measured. A moderate overdose of methamphetamine may induce symptoms such as: abnormal heart rhythm, confusion, difficult and/or painful urination, high or low blood pressure, high body temperature, over-active and/or over-responsive reflexes, muscle aches, severe agitation, rapid breathing, tremor, urinary hesitancy, and an inability to pass urine. [5] [42] An extremely large overdose may produce symptoms such as adrenergic storm, methamphetamine psychosis, substantially reduced or no urine output, cardiogenic shock, bleeding in the brain, circulatory collapse, hyperpy rexia (i.e., dangerously high body temperature), pulmonary hypertension, kidney failure, rapid muscle breakdown, serotonin syndrome, and a form of stereotypy ("tweaking"). [sources 1] A methamphetamine overdose will likely also result in mild brain damage owing to dopaminergic and serotonergic neurotoxicity. [106] [30] Death from methamphetamine poisoning is typically preceded by convulsions and coma. [25]
Use of methamphetamine can result in a stimulant psychosis which may present with a variety of symptoms (e.g., paranoia, hallucinations, delirium, and delusions). [5] [107] A Cochrane Collaboration review on treatment for amphetamine, dextroamphetamine, and methamphetamine use-induced psychosis states that about 5–15% of users fail to recover completely. [107] [108] The same review asserts that, based upon at least one trial, antipsychotic medications effectively resolve the symptoms of acute amphetamine psychosis. [107] Amphetamine psychosis may also develop occasionally as a treatment-emergent side effect. [109]
The CDC reported that the number of deaths in the United States involving psychostimulants with abuse potential to be 23,837 in 2020 and 32,537 in 2021. [110] This category code (ICD–10 of T43.6) includes primarily methamphetamine but also other stimulants such as amphetamine, and methylphenidate. The mechanism of death in these cases is not reported in these statistics and is difficult to know. [111] Unlike fentanyl which causes respiratory depression, methamphetamine is not a respiratory depressant. Some deaths are as a result of intracranial hemorrhage [112] and some deaths are cardiovascular in nature including flash pulmonary edema [113] and ventricular fibrillation. [114] [115]
Acute methamphetamine intoxication is largely managed by treating the symptoms and treatments may initially include administration of activated charcoal and sedation. [5] There is not enough evidence on hemodialysis or peritoneal dialysis in cases of methamphetamine intoxication to determine their usefulness. [25] Forced acid diuresis (e.g., with vitamin C) will increase methamphetamine excretion but is not recommended as it may increase the risk of aggravating acidosis, or cause seizures or rhabdomyolysis. [5] Hypertension presents a risk for intracranial hemorrhage (i.e., bleeding in the brain) and, if severe, is typically treated with intravenous phentolamine or nitroprusside. [5] Blood pressure often drops gradually following sufficient sedation with a benzodiazepine and providing a calming environment. [5]
Antipsychotics such as haloperidol are useful in treating agitation and psychosis from methamphetamine overdose. [116] [117] Beta blockers with lipophilic properties and CNS penetration such as metoprolol and labetalol may be useful for treating CNS and cardiovascular toxicity. [118] [ failed verification ] The mixed alpha- and beta-blocker labetalol is especially useful for treatment of concomitant tachycardia and hypertension induced by methamphetamine. [116] The phenomenon of "unopposed alpha stimulation" has not been reported with the use of beta-blockers for treatment of methamphetamine toxicity. [116]
Methamphetamine is metabolized by the liver enzyme CYP2D6, so CYP2D6 inhibitors will prolong the elimination half-life of methamphetamine. [25] [119] Methamphetamine also interacts with monoamine oxidase inhibitors (MAOIs), since both MAOIs and methamphetamine increase plasma catecholamines; therefore, concurrent use of both is dangerous. [25] Methamphetamine may decrease the effects of sedatives and depressants and increase the effects of antidepressants and other stimulants as well. [25] Methamphetamine may counteract the effects of antihypertensives and antipsychotics owing to its effects on the cardiovascular system and cognition respectively. [25] The pH of gastrointestinal content and urine affects the absorption and excretion of methamphetamine. [25] Specifically, acidic substances will reduce the absorption of methamphetamine and increase urinary excretion, while alkaline substances do the opposite. [25] Owing to the effect pH has on absorption, proton pump inhibitors, which reduce gastric acid, are known to interact with methamphetamine. [25]
Compound | NE | DA | 5-HT | Ref | ||
---|---|---|---|---|---|---|
Phenethylamine | 10.9 | 39.5 | >10,000 | [120] [121] [122] | ||
Dextroamphetamine | 6.6–7.2 | 5.8–24.8 | 698–1,765 | [123] [124] | ||
Levoamphetamine | 9.5 | 27.7 | ND | [121] [122] | ||
Dextromethamphetamine | 12.3–13.8 | 8.5–24.5 | 736–1,292 | [123] [125] | ||
Levomethamphetamine | 28.5 | 416 | 4,640 | [123] | ||
Notes: The smaller the value, the more strongly the drug releases the neurotransmitter. See also Monoamine releasing agent § Activity profiles for a larger table with more compounds. Refs: [126] [127] |
Methamphetamine has been identified as a potent full agonist of trace amine-associated receptor 1 (TAAR1), a G protein-coupled receptor (GPCR) that regulates brain catecholamine systems. [128] [129] Activation of TAAR1 increases cyclic adenosine monophosphate (cAMP) production and either completely inhibits or reverses the transport direction of the dopamine transporter (DAT), norepinephrine transporter (NET), and serotonin transporter (SERT). [128] [130] When methamphetamine binds to TAAR1, it triggers transporter phosphorylation via protein kinase A (PKA) and protein kinase C (PKC) signaling, ultimately resulting in the internalization or reverse function of monoamine transporters. [128] [131] Methamphetamine is also known to increase intracellular calcium, an effect which is associated with DAT phosphorylation through a Ca2+/calmodulin-dependent protein kinase (CAMK)-dependent signaling pathway, in turn producing dopamine efflux. [132] [133] [134] TAAR1 has been shown to reduce the firing rate of neurons through direct activation of G protein-coupled inwardly-rectifying potassium channels. [135] [136] [137] TAAR1 activation by methamphetamine in astrocytes appears to negatively modulate the membrane expression and function of EAAT2, a type of glutamate transporter. [61]
In addition to its effect on the plasma membrane monoamine transporters, methamphetamine inhibits synaptic vesicle function by inhibiting VMAT2, which prevents monoamine uptake into the vesicles and promotes their release. [138] This results in the outflow of monoamines from synaptic vesicles into the cytosol (intracellular fluid) of the presynaptic neuron, and their subsequent release into the synaptic cleft by the phosphorylated transporters. [139] Other transporters that methamphetamine is known to inhibit are SLC22A3 and SLC22A5. [138] SLC22A3 is an extraneuronal monoamine transporter that is present in astrocytes, and SLC22A5 is a high-affinity carnitine transporter. [129] [140]
Methamphetamine is also an agonist of the alpha-2 adrenergic receptors and sigma receptors with a greater affinity for σ1 than σ2, and inhibits monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). [59] [129] [63] Sigma receptor activation by methamphetamine may facilitate its central nervous system stimulant effects and promote neurotoxicity within the brain. [59] [63] Dextromethamphetamine is a stronger psychostimulant, but levomethamphetamine has stronger peripheral effects, a longer half-life, and longer perceived effects among heavy substance users. [141] [142] [143] At high doses, both enantiomers of methamphetamine can induce similar stereotypy and methamphetamine psychosis, [142] but levomethamphetamine has shorter psychodynamic effects. [143]
The bioavailability of methamphetamine is 67% orally, 79% intranasally, 67 to 90% via inhalation (smoking), and 100% intravenously. [4] [5] [6] Following oral administration, methamphetamine is well-absorbed into the bloodstream, with peak plasma methamphetamine concentrations achieved in approximately 3.13–6.3 hours post ingestion. [144] Methamphetamine is also well absorbed following inhalation and following intranasal administration. [5] Because of the high lipophilicity of methamphetamine due to its methyl group, it can readily move through the blood–brain barrier faster than other stimulants, where it is more resistant to degradation by monoamine oxidase. [5] [144] [145] The amphetamine metabolite peaks at 10–24 hours. [5] Methamphetamine is excreted by the kidneys, with the rate of excretion into the urine heavily influenced by urinary pH. [25] [144] When taken orally, 30–54% of the dose is excreted in urine as methamphetamine and 10–23% as amphetamine. [144] Following IV doses, about 45% is excreted as methamphetamine and 7% as amphetamine. [144] The elimination half-life of methamphetamine varies with a range of 5–30 hours, but it is on average 9 to 12 hours in most studies. [5] [4] The elimination half-life of methamphetamine does not vary by route of administration, but is subject to substantial interindividual variability. [4]
CYP2D6, dopamine β-hydroxylase, flavin-containing monooxygenase 3, butyrate-CoA ligase, and glycine N-acyltransferase are the enzymes known to metabolize methamphetamine or its metabolites in humans. [sources 2] The primary metabolites are amphetamine and 4-hydroxymethamphetamine; [144] other minor metabolites include: 4-hydroxyamphetamine , 4-hydroxynorephedrine , 4-hydroxyphenylacetone , benzoic acid, hippuric acid, norephedrine, and phenylacetone, the metabolites of amphetamine. [10] [144] [146] Among these metabolites, the active sympathomimetics are amphetamine, 4‑hydroxyamphetamine, [152] 4‑hydroxynorephedrine, [153] 4-hydroxymethamphetamine, [144] and norephedrine. [154] Methamphetamine is a CYP2D6 inhibitor. [119]
The main metabolic pathways involve aromatic para-hydroxylation, aliphatic alpha- and beta-hydroxylation, N-oxidation, N-dealkylation, and deamination. [10] [144] [155] The known metabolic pathways include:
Metabolic pathways of methamphetamine in humans [sources 2] |
Methamphetamine and amphetamine are often measured in urine or blood as part of a drug test for sports, employment, poisoning diagnostics, and forensics. [158] [159] [160] [161] Chiral techniques may be employed to help distinguish the source of the drug to determine whether it was obtained illicitly or legally via prescription or prodrug. [162] Chiral separation is needed to assess the possible contribution of levomethamphetamine, which is an active ingredients in some OTC nasal decongestants, [note 4] toward a positive test result. [162] [163] [164] Dietary zinc supplements can mask the presence of methamphetamine and other drugs in urine. [165]
Methamphetamine is a chiral compound with two enantiomers, dextromethamphetamine and levomethamphetamine. At room temperature, the free base of methamphetamine is a clear and colorless liquid with an odor characteristic of geranium leaves. [13] It is soluble in diethyl ether and ethanol as well as miscible with chloroform. [13]
In contrast, the methamphetamine hydrochloride salt is odorless with a bitter taste. [13] It has a melting point between 170 and 175 °C (338 and 347 °F) and, at room temperature, occurs as white crystals or a white crystalline powder. [13] The hydrochloride salt is also freely soluble in ethanol and water. [13] The crystal structure of either enantiomer is monoclinic with P21 space group; at 90 K (−183.2 °C; −297.7 °F), it has lattice parameters a = 7.10 Å, b = 7.29 Å, c = 10.81 Å, and β = 97.29°. [166]
A 2011 study into the destruction of methamphetamine using bleach showed that effectiveness is correlated with exposure time and concentration. [167] A year-long study (also from 2011) showed that methamphetamine in soils is a persistent pollutant. [168] In a 2013 study of bioreactors in wastewater, methamphetamine was found to be largely degraded within 30 days under exposure to light. [169]
Racemic methamphetamine may be prepared starting from phenylacetone by either the Leuckart [170] or reductive amination methods. [171] In the Leuckart reaction, one equivalent of phenylacetone is reacted with two equivalents of N-methylformamide to produce the formyl amide of methamphetamine plus carbon dioxide and methylamine as side products. [171] In this reaction, an iminium cation is formed as an intermediate which is reduced by the second equivalent of N-methylformamide. [171] The intermediate formyl amide is then hydrolyzed under acidic aqueous conditions to yield methamphetamine as the final product. [171] Alternatively, phenylacetone can be reacted with methylamine under reducing conditions to yield methamphetamine. [171]
Amphetamine, discovered before methamphetamine, was first synthesized in 1887 in Germany by Romanian chemist Lazăr Edeleanu who named it phenylisopropylamine. [174] [175] Shortly after, methamphetamine was synthesized from ephedrine in 1893 by Japanese chemist Nagai Nagayoshi. [176] Three decades later, in 1919, methamphetamine hydrochloride was synthesized by pharmacologist Akira Ogata via reduction of ephedrine using red phosphorus and iodine. [177]
From 1938, methamphetamine was marketed on a large scale in Germany as a nonprescription drug under the brand name Pervitin, produced by the Berlin-based Temmler pharmaceutical company. [178] [179] It was used by all branches of the combined armed forces of the Third Reich, for its stimulant effects and to induce extended wakefulness. [180] [181] Pervitin became colloquially known among the German troops as "Stuka-Tablets" (Stuka-Tabletten) and "Herman-Göring-Pills" (Hermann-Göring-Pillen), as a snide allusion to Göring's widely-known addiction to drugs. However, the side effects, particularly the withdrawal symptoms, were so serious that the army sharply cut back its usage in 1940. [182] By 1941, usage was restricted to a doctor's prescription, and the military tightly controlled its distribution. Soldiers would only receive a couple of tablets at a time, and were discouraged from using them in combat. Historian Łukasz Kamieński says,
A soldier going to battle on Pervitin usually found himself unable to perform effectively for the next day or two. Suffering from a drug hangover and looking more like a zombie than a great warrior, he had to recover from the side effects.
Some soldiers turned violent, committing war crimes against civilians; others attacked their own officers. [182] At the end of the war, it was used as part of a new drug: D-IX.
Obetrol, patented by Obetrol Pharmaceuticals in the 1950s and indicated for treatment of obesity, was one of the first brands of pharmaceutical methamphetamine products. [183] Because of the psychological and stimulant effects of methamphetamine, Obetrol became a popular diet pill in America in the 1950s and 1960s. [183] Eventually, as the addictive properties of the drug became known, governments began to strictly regulate the production and distribution of methamphetamine. [175] For example, during the early 1970s in the United States, methamphetamine became a schedule II controlled substance under the Controlled Substances Act. [184] Currently, methamphetamine is sold under the trade name Desoxyn, trademarked by the Danish pharmaceutical company Lundbeck. [185] As of January 2013, the Desoxyn trademark had been sold to Italian pharmaceutical company Recordati. [186]
The Golden Triangle (Southeast Asia), specifically Shan State, Myanmar, is the world's leading producer of methamphetamine as production has shifted to Yaba and crystalline methamphetamine, including for export to the United States and across East and Southeast Asia and the Pacific. [187]
Concerning the accelerating synthetic drug production in the region, the Cantonese Chinese syndicate Sam Gor, also known as The Company, is understood to be the main international crime syndicate responsible for this shift. [188] It is made up of members of five different triads. Sam Gor is primarily involved in drug trafficking, earning at least $8 billion per year. [189] Sam Gor is alleged to control 40% of the Asia-Pacific methamphetamine market, while also trafficking heroin and ketamine. The organization is active in a variety of countries, including Myanmar, Thailand, New Zealand, Australia, Japan, China, and Taiwan. Sam Gor previously produced meth in Southern China and is now believed to manufacture mainly in the Golden Triangle, specifically Shan State, Myanmar, responsible for much of the massive surge of crystal meth in circa 2019. [190] The group is understood to be headed by Tse Chi Lop, a gangster born in Guangzhou, China who also holds a Canadian passport.
Liu Zhaohua was another individual involved in the production and trafficking of methamphetamine until his arrest in 2005. [191] It was estimated over 18 tonnes of methamphetamine were produced under his watch. [191]
The production, distribution, sale, and possession of methamphetamine is restricted or illegal in many jurisdictions. [192] [193] In some jurisdictions, it is legally available as a prescription medication. Methamphetamine has been placed in schedule II of the United Nations Convention on Psychotropic Substances treaty, indicating that it has limited medical use. [193]
Animal models have shown that low-dose methamphetamine improves cognitive and behavioural functioning following TBI (traumatic brain injury). [7] This is in contrast to high, repeated doses which cause neurotoxicity. These models demonstrate that low-dose methamphetamine increases neurogenesis and reduces apoptosis in the dentate gyrus of the hippocampus following TBI. [194] It has also been found that TBI patients testing positive for methamphetamine at the time of emergency department admission have lower rates of mortality. [195]
It has been suggested, based on animal research, that calcitriol, the active metabolite of vitamin D, can provide significant protection against the DA- and 5-HT-depleting effects of neurotoxic doses of methamphetamine. [196] Protection against methamphetamine-induced neurotoxicity has also been observed following administration of ascorbic acid (vitamin C), [197] cobalamin (vitamin B12), [198] and vitamin E. [199]
Amphetamine is a central nervous system (CNS) stimulant that is used in the treatment of attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity; it is also used to treat binge eating disorder in the form of its inactive prodrug lisdexamfetamine. Amphetamine was discovered as a chemical in 1887 by Lazăr Edeleanu, and then as a drug in the late 1920s. It exists as two enantiomers: levoamphetamine and dextroamphetamine. Amphetamine properly refers to a specific chemical, the racemic free base, which is equal parts of the two enantiomers in their pure amine forms. The term is frequently used informally to refer to any combination of the enantiomers, or to either of them alone. Historically, it has been used to treat nasal congestion and depression. Amphetamine is also used as an athletic performance enhancer and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant. It is a prescription drug in many countries, and unauthorized possession and distribution of amphetamine are often tightly controlled due to the significant health risks associated with recreational use.
Stimulants are a class of drugs that increase alertness. They are used for various purposes, such as enhancing attention, motivation, cognition, mood, and physical performance. Some stimulants are naturally-occuring while others only occur synthetic. Some of the most common stimulants are caffeine, nicotine, amphetamines, cocaine, methylphenidate, and modafinil. Stimulants may be subject to varying forms of regulation, or outright prohibition, depending on jurisdiction.
The mesolimbic pathway, sometimes referred to as the reward pathway, is a dopaminergic pathway in the brain. The pathway connects the ventral tegmental area in the midbrain to the ventral striatum of the basal ganglia in the forebrain. The ventral striatum includes the nucleus accumbens and the olfactory tubercle.
Dextroamphetamine is a potent central nervous system (CNS) stimulant and enantiomer of amphetamine that is primarily prescribed for the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It is also used as an athletic performance and cognitive enhancer, and recreationally as an aphrodisiac and euphoriant. Dextroamphetamine is generally regarded as the prototypical stimulant.
The nucleus accumbens is a region in the basal forebrain rostral to the preoptic area of the hypothalamus. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum. The ventral striatum and dorsal striatum collectively form the striatum, which is the main component of the basal ganglia. The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle. Each cerebral hemisphere has its own nucleus accumbens, which can be divided into two structures: the nucleus accumbens core and the nucleus accumbens shell. These substructures have different morphology and functions.
Adderall and Mydayis are trade names for a combination drug containing four salts of amphetamine. The mixture is composed of equal parts racemic amphetamine and dextroamphetamine, which produces a (3:1) ratio between dextroamphetamine and levoamphetamine, the two enantiomers of amphetamine. Both enantiomers are stimulants, but differ enough to give Adderall an effects profile distinct from those of racemic amphetamine or dextroamphetamine, which are marketed as Evekeo and Dexedrine/Zenzedi, respectively. Adderall is used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It is also used illicitly as an athletic performance enhancer, cognitive enhancer, appetite suppressant, and recreationally as a euphoriant. It is a central nervous system (CNS) stimulant of the phenethylamine class.
Levmetamfetamine, also known as l-desoxyephedrine or levomethamphetamine, and commonly sold under the brand name Vicks VapoInhaler among others, is an optical isomer of methamphetamine primarily used as a topical nasal decongestant. It is used to treat nasal congestion from allergies and the common cold. It was first used medically as decongestant beginning in 1958 and has been used for such purposes, primarily in the United States, since then.
Naphthylaminopropane, also known as naphthylisopropylamine (NIPA), is an experimental drug that was under investigation for the treatment of alcohol and stimulant addiction.
Trace amine-associated receptor 1 (TAAR1) is a trace amine-associated receptor (TAAR) protein that in humans is encoded by the TAAR1 gene. TAAR1 is an intracellular amine-activated Gs-coupled and Gq-coupled G protein-coupled receptor (GPCR) that is primarily expressed in several peripheral organs and cells, astrocytes, and in the intracellular milieu within the presynaptic plasma membrane of monoamine neurons in the central nervous system (CNS). TAAR1 was discovered in 2001 by two independent groups of investigators, Borowski et al. and Bunzow et al. TAAR1 is one of six functional human trace amine-associated receptors, which are so named for their ability to bind endogenous amines that occur in tissues at trace concentrations. TAAR1 plays a significant role in regulating neurotransmission in dopamine, norepinephrine, and serotonin neurons in the CNS; it also affects immune system and neuroimmune system function through different mechanisms.
Protein fosB, also known as FosB and G0/G1 switch regulatory protein 3 (G0S3), is a protein that in humans is encoded by the FBJ murine osteosarcoma viral oncogene homolog B (FOSB) gene.
para-Chloroamphetamine (PCA), also known as 4-chloroamphetamine (4-CA), is a serotonin–norepinephrine–dopamine releasing agent (SNDRA) and serotonergic neurotoxin of the amphetamine family. It is used in scientific research in the study of the serotonin system, as a serotonin releasing agent (SRA) at lower doses to produce serotonergic effects, and as a serotonergic neurotoxin at higher doses to produce long-lasting depletions of serotonin.
MDAI, also known as 5,6-methylenedioxy-2-aminoindane, is an entactogen drug of the 2-aminoindane group which is related to MDMA and produces similar subjective effects.
A monoamine releasing agent (MRA), or simply monoamine releaser, is a drug that induces the release of one or more monoamine neurotransmitters from the presynaptic neuron into the synapse, leading to an increase in the extracellular concentrations of the neurotransmitters and hence enhanced signaling by those neurotransmitters. The monoamine neurotransmitters include serotonin, norepinephrine, and dopamine; MRAs can induce the release of one or more of these neurotransmitters.
A dopamine releasing agent (DRA) is a type of drug which induces the release of dopamine in the body and/or brain.
Amphetamine dependence refers to a state of psychological dependence on a drug in the amphetamine class. Stimulants such as amphetamines and cocaine do not cause somatic symptoms upon cessation of use but rather neurological-based mental symptoms.
Addiction is a neuropsychological disorder characterized by a persistent and intense urge to use a drug or engage in a behavior that produces natural reward, despite substantial harm and other negative consequences. Repetitive drug use often alters brain function in ways that perpetuate craving and weakens self-control. This phenomenon – drugs reshaping brain function – has led to an understanding of addiction as a brain disorder with a complex variety of psychosocial as well as neurobiological factors that are implicated in the development of addiction.
Treatment and management of addiction encompass the range of approaches aimed at helping individuals overcome addiction, most commonly in the form of substance use disorders and behavioral addictions. Effective treatment often includes a combination of medical, psychological, and social interventions tailored to the specific needs of the individual. Common practices to this end include detoxification, counseling, behavioral therapy, medication-assisted treatment, and support groups. The goal of addiction treatment is to reduce dependence, improve quality of life, and ultimately support long-term recovery. Comprehensive management addresses both the physical and psychological aspects of addiction, recognizing it as a chronic but treatable condition.
Amphetamine type stimulants (ATS) are a group of synthetic drugs that are chemical derivatives of the parent compound alpha-methylphenethylamine, also known as amphetamine. Common ATS includes amphetamine, methamphetamine, ephedrine, pseudoephedrine, 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxyethylamphetamine (MDEA). ATS when used illicitly has street names including ice, meth, crystal, crank, bennies, and speed. Within the group of amphetamine-type stimulants, there are also prescription drugs including mixed amphetamine salts, dextroamphetamine, and lisdexamfetamine.
Disorders of diminished motivation (DDM) are a group of disorders involving diminished motivation and associated emotions. Many different terms have been used to refer to diminished motivation. Often however, a spectrum is defined encompassing apathy, abulia, and akinetic mutism, with apathy the least severe and akinetic mutism the most extreme.
RO5203648 is a trace amine-associated receptor 1 (TAAR1) partial agonist. It is a potent and highly selective partial agonist of both rodent and primate TAAR1. The drug suppresses the effects of psychostimulants like cocaine and methamphetamine. It also produces a variety of other behavioral effects, such as antidepressant-like, antipsychotic-like, and antiaddictive effects. Research with RO5203648 has led to interest in TAAR1 agonists for potential treatment of drug addiction. RO5203648 itself was not developed for potential medical use due to poor expected human pharmacokinetics.
Methamphetamine, a central nervous system stimulant drug, is p-hydroxylated by CYP2D6 to less active p-OH-methamphetamine.
The term metamfetamine (the International Non-Proprietary Name: INN) strictly relates to the specific enantiomer (S)-N,α-dimethylbenzeneethanamine.
METH is a schedule II drug, which can only be prescribed for attention deficit hyperactivity disorder (ADHD), extreme obesity, or narcolepsy (as Desoxyn; Recordati Rare Diseases LLC, Lebanon, NJ), with amphetamine being prescribed more often for these conditions due to amphetamine having lower reinforcing potential than METH (Lile et al., 2013). ...
As discussed earlier, the d-enantiomer has stronger CNS effects but is metabolized more quickly than the l-enantiomer, which is longer lasting due to the slower breakdown. ...
l-METH, a vasoconstrictor, is the active constituent of the Vicks Inhaler decongestant (Proctor & Gamble, Cincinnati, OH), an over-the-counter product containing about 50 mg of the drug (Smith et al., 2014). Desoxyn, which is d-METH, is rarely medically prescribed due to its strong reinforcing properties. Therapeutic doses of Desoxyn are 20–25 mg daily, taken every 12 hours, with dosing not exceeding 60 mg/day
Topical nasal decongestants --(i) For products containing levmetamfetamine identified in 341.20(b)(1) when used in an inhalant dosage form. The product delivers in every 800 milliliters of air 0.04 to 0.150 milligrams of levmetamfetamine.
Neuroimaging studies have revealed that METH can indeed cause neurodegenerative changes in the brains of human addicts (Aron and Paulus, 2007; Chang et al., 2007). These abnormalities include persistent decreases in the levels of dopamine transporters (DAT) in the orbitofrontal cortex, dorsolateral prefrontal cortex, and the caudate-putamen (McCann et al., 1998, 2008; Sekine et al., 2003; Volkow et al., 2001a, 2001c). The density of serotonin transporters (5-HTT) is also decreased in the midbrain, caudate, putamen, hypothalamus, thalamus, the orbitofrontal, temporal, and cingulate cortices of METH-dependent individuals (Sekine et al., 2006) ...
Neuropsychological studies have detected deficits in attention, working memory, and decision-making in chronic METH addicts ...
There is compelling evidence that the negative neuropsychiatric consequences of METH abuse are due, at least in part, to drug-induced neuropathological changes in the brains of these METH-exposed individuals ...
Structural magnetic resonance imaging (MRI) studies in METH addicts have revealed substantial morphological changes in their brains. These include loss of gray matter in the cingulate, limbic and paralimbic cortices, significant shrinkage of hippocampi, and hypertrophy of white matter (Thompson et al., 2004). In addition, the brains of METH abusers show evidence of hyperintensities in white matter (Bae et al., 2006; Ernst et al., 2000), decreases in the neuronal marker, N-acetylaspartate (Ernst et al., 2000; Sung et al., 2007), reductions in a marker of metabolic integrity, creatine (Sekine et al., 2002) and increases in a marker of glial activation, myoinositol (Chang et al., 2002; Ernst et al., 2000; Sung et al., 2007; Yen et al., 1994). Elevated choline levels, which are indicative of increased cellular membrane synthesis and turnover are also evident in the frontal gray matter of METH abusers (Ernst et al., 2000; Salo et al., 2007; Taylor et al., 2007).
Methamphetamine (INN: metamfetamine) is the N-methyl derivative of amphetamine. Unlike amfetamine (INN) which corresponds to the racemic mixture, metamfetamine (INN) refers to the dextro-isomer of l-phenyl-2-methylaminopropane.
Glia (including astrocytes, microglia, and oligodendrocytes), which constitute the majority of cells in the brain, have many of the same receptors as neurons, secrete neurotransmitters and neurotrophic and neuroinflammatory factors, control clearance of neurotransmitters from synaptic clefts, and are intimately involved in synaptic plasticity. Despite their prevalence and spectrum of functions, appreciation of their potential general importance has been elusive since their identification in the mid-1800s, and only relatively recently have they been gaining their due respect. This development of appreciation has been nurtured by the growing awareness that drugs of abuse, including the psychostimulants, affect glial activity, and glial activity, in turn, has been found to modulate the effects of the psychostimulants
Collectively, these pathological processes contribute to neurotoxicity (e.g., increased BBB permeability, inflammation, neuronal degeneration, cell death) and neuropsychiatric impairments (e.g., cognitive deficits, mood disorders)
σ Receptors seem to play an important role in many of the effects of METH. They are present in the organs that mediate the actions of METH (e.g. brain, heart, lungs) [5]. In the brain, METH acts primarily on the dopaminergic system to cause acute locomotor stimulant, subchronic sensitized, and neurotoxic effects. σ Receptors are present on dopaminergic neurons and their activation stimulates dopamine synthesis and release [11–13]. σ-2 Receptors modulate DAT and the release of dopamine via protein kinase C (PKC) and Ca2+-calmodulin systems [14].
σ-1 Receptor antisense and antagonists have been shown to block the acute locomotor stimulant effects of METH [4]. Repeated administration or self administration of METH has been shown to upregulate σ-1 receptor protein and mRNA in various brain regions including the substantia nigra, frontal cortex, cerebellum, midbrain, and hippocampus [15, 16]. Additionally, σ receptor antagonists ... prevent the development of behavioral sensitization to METH [17, 18]. ...
σ Receptor agonists have been shown to facilitate dopamine release, through both σ-1 and σ-2 receptors [11–14].
TAAR1 overexpression significantly decreased EAAT-2 levels and glutamate clearance ... METH treatment activated TAAR1 leading to intracellular cAMP in human astrocytes and modulated glutamate clearance abilities. Furthermore, molecular alterations in astrocyte TAAR1 levels correspond to changes in astrocyte EAAT-2 levels and function.
TAAR1 is largely located in the intracellular compartments both in neurons (Miller, 2011), in glial cells (Cisneros and Ghorpade, 2014) and in peripheral tissues (Grandy, 2007)
Despite the importance of numerous psychosocial factors, at its core, drug addiction involves a biological process: the ability of repeated exposure to a drug of abuse to induce changes in a vulnerable brain that drive the compulsive seeking and taking of drugs, and loss of control over drug use, that define a state of addiction. ... A large body of literature has demonstrated that such ΔFosB induction in D1-type [nucleus accumbens] neurons increases an animal's sensitivity to drug as well as natural rewards and promotes drug self-administration, presumably through a process of positive reinforcement ... Another ΔFosB target is cFos: as ΔFosB accumulates with repeated drug exposure it represses c-Fos and contributes to the molecular switch whereby ΔFosB is selectively induced in the chronic drug-treated state.41. ... Moreover, there is increasing evidence that, despite a range of genetic risks for addiction across the population, exposure to sufficiently high doses of a drug for long periods of time can transform someone who has relatively lower genetic loading into an addict.
Substance-use disorder: A diagnostic term in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) referring to recurrent use of alcohol or other drugs that causes clinically and functionally significant impairment, such as health problems, disability, and failure to meet major responsibilities at work, school, or home. Depending on the level of severity, this disorder is classified as mild, moderate, or severe.
Addiction: A term used to indicate the most severe, chronic stage of substance-use disorder, in which there is a substantial loss of self-control, as indicated by compulsive drug taking despite the desire to stop taking the drug. In the DSM-5, the term addiction is synonymous with the classification of severe substance-use disorder.
[Psychostimulants] increase cAMP levels in striatum, which activates protein kinase A (PKA) and leads to phosphorylation of its targets. This includes the cAMP response element binding protein (CREB), the phosphorylation of which induces its association with the histone acetyltransferase, CREB binding protein (CBP) to acetylate histones and facilitate gene activation. This is known to occur on many genes including fosB and c-fos in response to psychostimulant exposure. ΔFosB is also upregulated by chronic psychostimulant treatments, and is known to activate certain genes (eg, cdk5) and repress others (eg, c-fos) where it recruits HDAC1 as a corepressor. ... Chronic exposure to psychostimulants increases glutamatergic [signaling] from the prefrontal cortex to the NAc. Glutamatergic signaling elevates Ca2+ levels in NAc postsynaptic elements where it activates CaMK (calcium/calmodulin protein kinases) signaling, which, in addition to phosphorylating CREB, also phosphorylates HDAC5.
Coincident and convergent input often induces plasticity on a postsynaptic neuron. The NAc integrates processed information about the environment from basolateral amygdala, hippocampus, and prefrontal cortex (PFC), as well as projections from midbrain dopamine neurons. Previous studies have demonstrated how dopamine modulates this integrative process. For example, high frequency stimulation potentiates hippocampal inputs to the NAc while simultaneously depressing PFC synapses (Goto and Grace, 2005). The converse was also shown to be true; stimulation at PFC potentiates PFC–NAc synapses but depresses hippocampal–NAc synapses. In light of the new functional evidence of midbrain dopamine/glutamate co-transmission (references above), new experiments of NAc function will have to test whether midbrain glutamatergic inputs bias or filter either limbic or cortical inputs to guide goal-directed behavior.
Most addictive drugs increase extracellular concentrations of dopamine (DA) in nucleus accumbens (NAc) and medial prefrontal cortex (mPFC), projection areas of mesocorticolimbic DA neurons and key components of the "brain reward circuit". Amphetamine achieves this elevation in extracellular levels of DA by promoting efflux from synaptic terminals. ... Chronic exposure to amphetamine induces a unique transcription factor delta FosB, which plays an essential role in long-term adaptive changes in the brain.
ΔFosB serves as one of the master control proteins governing this structural plasticity. ... ΔFosB also represses G9a expression, leading to reduced repressive histone methylation at the cdk5 gene. The net result is gene activation and increased CDK5 expression. ... In contrast, ΔFosB binds to the c-fos gene and recruits several co-repressors, including HDAC1 (histone deacetylase 1) and SIRT 1 (sirtuin 1). ... The net result is c-fos gene repression.
The 35-37 kD ΔFosB isoforms accumulate with chronic drug exposure due to their extraordinarily long half-lives. ... As a result of its stability, the ΔFosB protein persists in neurons for at least several weeks after cessation of drug exposure. ... ΔFosB overexpression in nucleus accumbens induces NFκB ... In contrast, the ability of ΔFosB to repress the c-Fos gene occurs in concert with the recruitment of a histone deacetylase and presumably several other repressive proteins such as a repressive histone methyltransferase
Recent evidence has shown that ΔFosB also represses the c-fos gene that helps create the molecular switch—from the induction of several short-lived Fos family proteins after acute drug exposure to the predominant accumulation of ΔFosB after chronic drug exposure
ΔFosB has been linked directly to several addiction-related behaviors ... Importantly, genetic or viral overexpression of ΔJunD, a dominant-negative mutant of JunD which antagonizes ΔFosB- and other AP-1-mediated transcriptional activity, in the NAc or OFC blocks these key effects of drug exposure14,22–24. This indicates that ΔFosB is both necessary and sufficient for many of the changes wrought in the brain by chronic drug exposure. ΔFosB is also induced in D1-type NAc MSNs by chronic consumption of several natural rewards, including sucrose, high-fat food, sex, wheel running, where it promotes that consumption14,26–30. This implicates ΔFosB in the regulation of natural rewards under normal conditions and perhaps during pathological addictive-like states.
ΔFosB is an essential transcription factor implicated in the molecular and behavioral pathways of addiction following repeated drug exposure.
Similar to environmental enrichment, studies have found that exercise reduces self-administration and relapse to drugs of abuse (Cosgrove et al., 2002; Zlebnik et al., 2010). There is also some evidence that these preclinical findings translate to human populations, as exercise reduces withdrawal symptoms and relapse in abstinent smokers (Daniel et al., 2006; Prochaska et al., 2008), and one drug recovery program has seen success in participants that train for and compete in a marathon as part of the program (Butler, 2005). ... In humans, the role of dopamine signaling in incentive-sensitization processes has recently been highlighted by the observation of a dopamine dysregulation syndrome in some patients taking dopaminergic drugs. This syndrome is characterized by a medication-induced increase in (or compulsive) engagement in non-drug rewards such as gambling, shopping, or sex (Evans et al., 2006; Aiken, 2007; Lader, 2008).
It has been found that deltaFosB gene in the NAc is critical for reinforcing effects of sexual reward. Pitchers and colleagues (2010) reported that sexual experience was shown to cause DeltaFosB accumulation in several limbic brain regions including the NAc, medial pre-frontal cortex, VTA, caudate, and putamen, but not the medial preoptic nucleus. ... these findings support a critical role for DeltaFosB expression in the NAc in the reinforcing effects of sexual behavior and sexual experience-induced facilitation of sexual performance. ... both drug addiction and sexual addiction represent pathological forms of neuroplasticity along with the emergence of aberrant behaviors involving a cascade of neurochemical changes mainly in the brain's rewarding circuitry.
Drugs of abuse induce neuroplasticity in the natural reward pathway, specifically the nucleus accumbens (NAc), thereby causing development and expression of addictive behavior. ... Together, these findings demonstrate that drugs of abuse and natural reward behaviors act on common molecular and cellular mechanisms of plasticity that control vulnerability to drug addiction, and that this increased vulnerability is mediated by ΔFosB and its downstream transcriptional targets. ... Sexual behavior is highly rewarding (Tenk et al., 2009), and sexual experience causes sensitized drug-related behaviors, including cross-sensitization to amphetamine (Amph)-induced locomotor activity (Bradley and Meisel, 2001; Pitchers et al., 2010a) and enhanced Amph reward (Pitchers et al., 2010a). Moreover, sexual experience induces neural plasticity in the NAc similar to that induced by psychostimulant exposure, including increased dendritic spine density (Meisel and Mullins, 2006; Pitchers et al., 2010a), altered glutamate receptor trafficking, and decreased synaptic strength in prefrontal cortex-responding NAc shell neurons (Pitchers et al., 2012). Finally, periods of abstinence from sexual experience were found to be critical for enhanced Amph reward, NAc spinogenesis (Pitchers et al., 2010a), and glutamate receptor trafficking (Pitchers et al., 2012). These findings suggest that natural and drug reward experiences share common mechanisms of neural plasticity
Despite concerted efforts to identify a pharmacotherapy for managing stimulant use disorders, no widely effective medications have been approved.
The prevalence of this withdrawal syndrome is extremely common (Cantwell 1998; Gossop 1982) with 87.6% of 647 individuals with amphetamine dependence reporting six or more signs of amphetamine withdrawal listed in the DSM when the drug is not available (Schuckit 1999) ... Withdrawal symptoms typically present within 24 hours of the last use of amphetamine, with a withdrawal syndrome involving two general phases that can last 3 weeks or more. The first phase of this syndrome is the initial "crash" that resolves within about a week (Gossop 1982;McGregor 2005)
Unlike cocaine and amphetamine, methamphetamine is directly toxic at higher doses to midbrain dopamine neurons
A minority of individuals who use amphetamines develop full-blown psychosis requiring care at emergency departments or psychiatric hospitals. In such cases, symptoms of amphetamine psychosis commonly include paranoid and persecutory delusions as well as auditory and visual hallucinations in the presence of extreme agitation. More common (about 18%) is for frequent amphetamine users to report psychotic symptoms that are sub-clinical and that do not require high-intensity intervention ...
About 5–15% of the users who develop an amphetamine psychosis fail to recover completely (Hofmann 1983) ...
Findings from one trial indicate use of antipsychotic medications effectively resolves symptoms of acute amphetamine psychosis.
AMPH also increases intracellular calcium (Gnegy et al., 2004) that is associated with calmodulin/CamKII activation (Wei et al., 2007) and modulation and trafficking of the DAT (Fog et al., 2006; Sakrikar et al., 2012).
AMPH and METH also stimulate DA efflux, which is thought to be a crucial element in their addictive properties [80], although the mechanisms do not appear to be identical for each drug [81]. These processes are PKCβ– and CaMK–dependent [72, 82], and PKCβ knock-out mice display decreased AMPH-induced efflux that correlates with reduced AMPH-induced locomotion [72].
inhibition of firing due to increased release of dopamine; (b) reduction of D2 and GABAB receptor-mediated inhibitory responses (excitatory effects due to disinhibition); and (c) a direct TA1 receptor-mediated activation of GIRK channels which produce cell membrane hyperpolarization.
• tonically activates inwardly rectifying K(+) channels, which reduces the basal firing frequency of dopamine (DA) neurons of the ventral tegmental area (VTA)
Methamphetamine is rapidly absorbed from the gastrointestinal tract with peak methamphetamine concentrations occurring in 3.13 to 6.3 hours post ingestion. Methamphetamine is also well absorbed following inhalation and following intranasal administration. It is distributed to most parts of the body. Because methamphetamine has a high lipophilicity it is distributed across the blood brain barrier and crosses the placenta. ...
The primary site of metabolism is in the liver by aromatic hydroxylation, N-dealkylation and deamination. At least seven metabolites have been identified in the urine, with the main metabolites being amphetamine (active) and 4-hydroxymethamphetamine. Other minor metabolites include 4-hydroxyamphetamine, norephedrine, and 4-hydroxynorephedrine.
Methamphetamine (METH) is a potent amphetamine-type stimulant that has high abuse potential and can be smoked, snorted, injected, or taken orally. The drug is high in lipid solubility and can cross the blood-brain barrier more readily than amphetamine due to the addition of an extra methyl group.
The simplest unsubstituted phenylisopropylamine, 1-phenyl-2-aminopropane, or amphetamine, serves as a common structural template for hallucinogens and psychostimulants. Amphetamine produces central stimulant, anorectic, and sympathomimetic actions, and it is the prototype member of this class (39). ... The phase 1 metabolism of amphetamine analogs is catalyzed by two systems: cytochrome P450 and flavin monooxygenase. ... Amphetamine can also undergo aromatic hydroxylation to p-hydroxyamphetamine. ... Subsequent oxidation at the benzylic position by DA β-hydroxylase affords p-hydroxynorephedrine. Alternatively, direct oxidation of amphetamine by DA β-hydroxylase can afford norephedrine.
Dopamine-β-hydroxylase catalyzed the removal of the pro-R hydrogen atom and the production of 1-norephedrine, (2S,1R)-2-amino-1-hydroxyl-1-phenylpropane, from d-amphetamine.
Hydroxyamphetamine was administered orally to five human subjects ... Since conversion of hydroxyamphetamine to hydroxynorephedrine occurs in vitro by the action of dopamine-β-oxidase, a simple method is suggested for measuring the activity of this enzyme and the effect of its inhibitors in man. ... The lack of effect of administration of neomycin to one patient indicates that the hydroxylation occurs in body tissues. ... a major portion of the β-hydroxylation of hydroxyamphetamine occurs in non-adrenal tissue. Unfortunately, at the present time one cannot be completely certain that the hydroxylation of hydroxyamphetamine in vivo is accomplished by the same enzyme which converts dopamine to noradrenaline.