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).

[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.

[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.

Chronic high-dose use can precipitate unpredictable and rapid mood swings, stimulant psychosis (e.g., paranoia, hallucinations, delirium, and delusions), and violent behavior.

It is related to the other dimethylphenethylamines as a positional isomer of these compounds, which share the common chemical formula C10H15N.In the United States, methamphetamine hydrochloride, sold under the brand name Desoxyn, is FDA-approved for the treatment of attention deficit hyperactivity disorder (ADHD);[26][32] however, the FDA notes that the limited therapeutic usefulness of methamphetamine should be weighed against the risks associated with its use.

[24][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.

[35][36][37] 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.

[39] Participants in this subculture, which consists almost entirely of homosexual male methamphetamine users, will typically meet up through internet dating sites and have sex.

[42] 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.

[51] 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.

[53] 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.

[4] Magnetic resonance imaging studies on human methamphetamine users have also found evidence of neurodegeneration, or adverse neuroplastic changes in brain structure and function.

Current models of addiction from chronic drug use involve alterations in gene expression in certain parts of the brain, particularly the nucleus accumbens.

[note 7][79][84] 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.

[96] 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.

[101] Infants born to methamphetamine-abusing mothers may experience a neonatal withdrawal syndrome, with symptoms involving of abnormal sleep patterns, poor feeding, tremors, and hypertonia.

[5][43] 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").

[5][108] 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.

[115][116] Acute methamphetamine intoxication is largely managed by treating the symptoms and treatments may initially include administration of activated charcoal and sedation.

[137][140] 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.

[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.

[10][153][164] The known metabolic pathways include: Methamphetamine and amphetamine are often measured in urine or blood as part of a drug test for sports, employment, poisoning diagnostics, and forensics.

[171] 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.

[186] 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.

[189][190] 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.

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.

[204] 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.