Levomethamphetamine is the levorotatory (L-enantiomer) form of methamphetamine. Levomethamphetamine is a sympathomimetic vasoconstrictor that is the active ingredient in some over-the-counter (OTC) nasal decongestant inhalers in the United States. Pharmacology Levomethamphetamine crosses the blood-brain-barrier and acts as a TAAR1 agonist, functioning as a selective norepinephrine releasing agent (with few or no effects on the release of dopamine), so it affects the central nervous system, although its effects are qualitatively distinct relative to those of dextromethamphetamine. It does not possess the potential for euphoria or addiction that dextromethamphetamine possesses. Among its physiological effects are the vasoconstriction that makes it useful for nasal decongestion. The elimination half-life of levomethamphetamine is between 13.3 and 15 hours, whereas dextromethamphetamine has a half-life of about 10.5 hours. Selegiline Levomethamphetamine is an active metabolite of the antiparkinson's drug selegiline. Selegiline, a selective monoamine oxidase B (MAOB) inhibitor at low doses, is also metabolized into levomethamphetamine and levoamphetamine. This has caused users to test positive for amphetamines. Selegiline itself has neuroprotective and neuro-rescuing effects, but concern over the resulting levomethamphetamine's neurotoxicity led to development of alternative MAOB inhibitors, such as rasagiline, that do not produce toxic metabolites. Side effects When the nasal decongestant is taken in excess, levomethamphetamine has potential side effects resembling those of other sympathomimetic drugs; these effects include hypertension (elevated blood pressure), tachycardia (rapid heart rate), nausea, stomach cramps, dizziness, headache, sweating, muscle tension, and tremors. Central side effects may include anxiety, insomnia, and loss of appetite. Non-medicinal usage In a study of psychoactive effects of levomethamphetamine, the intravenous administration of 0.5 mg/kg (but not 0.25 mg/kg) in recreational methamphetamine users produced scores of "drug liking" similar to racemic methamphetamine, but the effects were shorter lived. The study did not test the oral administration of levomethamphetamine. As of 2006, there were no studies demonstrating "drug liking" scores of oral levomethamphetamine that are similar to racemic methamphetamine or dextromethamphetamine in either recreational users or medicinal users. Detection in body fluids Levomethamphetamine can register on urine drug screens as either methamphetamine, amphetamine, or both, depending on the subject's metabolism and dosage. L-methamphetamine metabolizes completely into L-amphetamine after a period of time. Notes References Methamphetamine Sympathomimetic amines Enantiopure drugs Norepinephrine releasing agents TAAR1 agonists VMAT inhibitors