Methamphetamine (contracted from ) 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 and its high potential for recreational use, among other concerns, and the availability of safer substitute drugs with comparable treatment efficacy. Methamphetamine exists as two enantiomers: dextromethamphetamine and levomethamphetamine. 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. Dextromethamphetamine is a much stronger central stimulant than levomethamphetamine. Both enantiomers are neurotoxic and addictive.