3,4-methylenedioxymethamphetamine (MDMA; commonly referred to as “ecstasy” or “molly”) is a substituted amphetamine drug that is used recreationally for its acute psychoactive effects, including euphoria and increased energy, as well as prosocial effects such as increased empathy and feelings of closeness with others. Acute adverse effects can include hyperthermia, dehydration, bruxism, and diaphoresis. Post-intoxication phenomena may include insomnia, anhedonia, anxiety, depression, and memory impairment, which can persist for days following drug cessation. MDMA acts as a releasing agent for monoamine neurotransmitters, including dopamine (DA), norepinephrine (NE) and serotonin (5-HT), by interfering with vesicular storage and transporter function, thus increasing extracellular levels of DA, NE, and 5-HT. Medical intervention in response to adverse events is complicated by the fact that illicitly-acquired MDMA is frequently adulterated, contaminated, or outright replaced with other psychoactive drugs such as synthetic cathinones (“bath salts”) or methamphetamine, often unknown to the person using the drug. This review provides background on the legal status of MDMA and its use patterns, including proposals for its use as an adjunct in psychotherapy. It also discusses the pharmacological properties, mental and physical health effects, and interactions of MDMA with other drugs, with special focus on harm reduction strategies. This information will help healthcare providers assess adverse health effects related to MDMA/ecstasy use in order to facilitate appropriate treatment strategies and improve patient outcomes.