Caffeine induces a profound and persistent tachycardia in response to MDMA ("Ecstasy") administration.

Caffeine promotes hyperthermia and lethality when co-administered with the recreational drug 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") to rats. In the present study, co-administration of caffeine (10 mg/kg, s.c.) with MDMA (10 mg/kg, s.c.) induced a profound tachycardic response compared to rats treated with either drug alone. However, neither caffeine (30 microM) nor MDMA (1-30 microM), alone or in combination, affected the electrocardiogram of the isolated heart suggesting that central and sympathomimetic actions, rather than direct actions of these drugs on the heart, are responsible for the tachycardia observed in vivo. This is a serious drug interaction, which could have important health consequences for recreational drug users.