MDMA (3,4-methylenedioxymethamphetamine), also known as "ecstasy," is a complex drug that defies simple classification. Its chemical structure bears similarities to both the stimulant methamphetamine and the hallucinogen mescaline. As a result it can produce both stimulant and psychedelic effects, though the latter are milder than those produced by true hallucinogens, such as LSD. Mixed stimulant and psychedelic effects plateau after approximately 2 hours and can continue for up to 6 hours. Ecstasy's pleasurable effects can include enhanced sense of pleasure and self-confidence, increased energy, and feelings of peacefulness, acceptance, and closeness with others. Such effects help explain ecstasy's popularity with adolescents and young adults in the United States who began using it in increasing numbers during the 1990s, particularly at nightclubs and raves.

Research has shown that, in addition to its euphoric effects, MDMA can lead to disruptions in body temperature and cardiovascular regulation. Environmental conditions, such as the extremely high temperatures found at many dance venues, and the drug's stimulant effects can increase the severity of these symptoms. This combination of circumstances can lead to dehydration, hypertension, hyperthermia, and heart or kidney failure. MDMA also damages nerves in the brain's serotonin system and appears to produce long-term deficits in memory and cognition.