Methamphetamine (contracted from N-methyl-alpha-methylphenethylamine) is a strong central nervous system (CNS) stimulant that is mainly used as a recreational drug. Methamphetamine hydrochloride is approved by the United States Food and Drug Administration (USFDA) under the trade name Desoxyn for attention deficit hyperactivity disorder and obesity in adults and children, and is sometimes prescribed off label for narcolepsy and idiopathic hypersomnia. It is rarely prescribed due to concerns involving human neurotoxicity, the availability of safer substitute drugs with comparable treatment efficacy, and the high potential for recreational use, among other concerns. Methamphetamine exists as two dextrorotary and levorotary enantiomers: dextromethamphetamine and levomethamphetamine. Methamphetamine properly refers to a specific chemical, the racemic free base, which is an equal parts mixture of levomethamphetamine and dextromethamphetamine in their pure amine forms. Dextromethamphetamine is a stronger CNS stimulant than levomethamphetamine; however, both enantiomers are neurotoxic and addictive.Both methamphetamine and enantiopure dextromethamphetamine are illicitly trafficked and sold due to their potential for recreational use as an aphrodisiac and euphoriant; the highest prevalence of illegal methamphetamine use occurs in parts of Asia, Oceania, and in the United States, where both racemic methamphetamine, levomethamphetamine, and dextromethamphetamine are classified as schedule II controlled substances; however, enantiopure levomethamphetamine is available as an over-the-counter drug for use as an inhaled nasal decongestant in the United States. Internationally, the production, distribution, sale, and possession of methamphetamine is restricted or banned in many other countries due to its placement in schedule II of the United Nations Convention on Psychotropic Substances treaty. While enantiopure dextromethamphetamine is a more potent drug than racemic methamphetamine, the racemic form is sometimes produced and sold instead of dextromethamphetamine due to the relative ease of its synthesis by certain methods and the limited availability of associated chemical precursors.In low doses, methamphetamine can elevate mood, increase alertness, concentration, and energy in fatigued individuals, reduce appetite and promote (initial) weight loss. At higher doses, it can induce psychosis, rhabdomyolysis and cerebral hemorrhage. Chronic high dose use can precipitate unpredictable and rapid mood swings, prominent delusions and violent behavior. Recreationally, methamphetamine's ability to increase energy has been reported to lift mood and increase sexual desire to an extent of users ability to engage in sexual activity continuously for several days. Methamphetamine is known to have a high addiction liability (i.e., compulsive methamphetamine use) and dependence liability (i.e., withdrawal symptoms occur when methamphetamine use ceases). Heavy recreational use of methamphetamine may lead to a post-acute-withdrawal syndrome, which can persist for months beyond the typical withdrawal period.[i] Unlike amphetamine, methamphetamine is neurotoxic to humans, damaging both dopamine and serotonin neurons in the CNS.[i] Contrary to the long-term use of amphetamine,[iii] there is evidence that methamphetamine causes brain damage from long-term use in humans;[ii] this damage includes adverse changes in brain structure and function, such as reductions in grey matter volume in several brain regions and adverse changes in markers of metabolic integrity.[ii]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: C10H15N1.