Abuse of the psychoactive “designer drug” methylenedioxypyrovalerone (MDPV) has become a serious international public health concern because of the severity of its physical and behavioral toxicities. MDPV is the primary ingredient in so-called “bath salts,” labeled as such to avoid criminal prosecution and has only been classified recently as a controlled substance in the United States and some other countries. However, it remains a danger because of illegal sources, including the Internet. MDPV is a synthetic, cathinone-derivative, central nervous system stimulant and is taken to produce a cocaine- or methamphetamine-like high. Administered via oral ingestion, nasal insufflation, smoking, intravenous or intramuscular methods, or the rectum, the intoxication lasts 6 to 8 hours and has high addictive potential. Overdoses are characterized by profound toxicities, causing increased attention by emergency department and law enforcement personnel. Physical manifestations range from tachycardia, hypertension, arrhythmias, hyperthermia, sweating, rhabdomyolysis, and seizures to those as severe as stroke, cerebral edema, cardiorespiratory collapse, myocardial infarction, and death. Behavioral effects include panic attacks, anxiety, agitation, severe paranoia, hallucinations, psychosis, suicidal ideation, self-mutilation, and behavior that is aggressive, violent, and self-destructive. Treatment is principally supportive and focuses on counteracting the sympathetic overstimulation, including sedation with intravenous benzodiazepines, seizure-prevention measures, intravenous fluids, close (eg, intensive care unit) monitoring, and restraints to prevent harm to self or others. Clinical presentation is often complicated by coingestion of other psychoactive substances that may alter the treatment approach. Clinicians need to be especially vigilant in that MDPV is not detected by routine drug screens and overdoses can be life-threatening.