Methamphetamine is a central nervous system stimulant used as a recreational drug and rarely as a second-line treatment for attention deficit hyperactivity disorder and obesity. It is seldom prescribed over concerns involving human neurotoxicity and potential for recreational abuse as an aphrodisiac and euphoriant.
The highest degree of illegal methamphetamine use occurs in parts of Asia and Oceania, as well as the United States, where it has been classified as a schedule II controlled substance. Levomethamphetamine is available in the United States as an over-the-counter drug for use as an inhaled nasal decongestant.
Recreationally, methamphetamine’s ability to increase energy has been reported to lift mood and increase sexual desire to such an extent that users are able to engage in sexual activity continuously for extensive periods during binges. At high doses, methamphetamine can induce psychosis, the breakdown of skeletal muscle, seizures and brain bleeding. Chronic high-dose intake can precipitate unpredictable mood swings, stimulant psychosis and violent behavior.
Methamphetamine is very addictive and there is a high likelihood that withdrawal symptoms will occur when methamphetamine use ceases. Withdrawal from methamphetamine use may lead to a post-acute-withdrawal syndrome, which can persist for months beyond the typical withdrawal period.
Methamphetamine is neurotoxic at high doses and has been shown to have a higher toxicity toward serotonergic neurons than amphetamine. Methamphetamine neurotoxicity causes deleterious changes in brain structure and function, such as reductions in gray matter volume.
A moderate overdose of methamphetamine may induce symptoms such as abnormal heart rhythm, confusion, difficult or painful urination, high or low blood pressure, high body temperature, over-active or over-responsive reflexes, muscle aches, rapid breathing, tremor, and an inability to pass urine.
A large overdose may produce symptoms such as adrenergic storm, methamphetamine psychosis, substantially reduced or no urine output, cardiogenic shock, circulatory collapse, pulmonary hypertension, kidney failure, rapid muscle breakdown and serotonin syndrome. A methamphetamine overdose will likely also result in brain damage owing to dopaminergic and serotonergic neurotoxicity. Death from methamphetamine poisoning is often preceded by convulsions and coma.
A Cochrane Collaboration review on treatment for amphetamine and methamphetamine-induced psychosis states that about 5–15% of users fail to recover completely. The same review asserts that antipsychotic medications can aid in the resolution of acute amphetamine psychosis symptoms.