Methamphetamine (contracted from N-methylamphetamine) is a strong central nervous system (CNS) stimulant that is mainly used as a recreational drug and less commonly as a treatment for attention deficit hyperactivity disorder and obesity. Methamphetamine was discovered in 1893 and exists as two enantiomers: levo-methamphetamine and dextro-methamphetamine.Methamphetamine properly refers to a specific chemical, the racemic free base, which is an equal mixture of levomethamphetamine and dextromethamphetamine in their pure amine forms. It is rarely prescribed due to concerns involving human neurotoxicity and 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. Dextromethamphetamine is a much stronger CNS stimulant than levomethamphetamine.
Both 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, Oceania, and in the United States, where racemic methamphetamine, levomethamphetamine, 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. Internationally, the production, distribution, sale, and possession of methamphetamine is restricted or banned in many countries, due 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 sometimes illicitly produced due to the relative ease of synthesis and limited availability of chemical precursors.