Pharmacological Interaction Between Doxazosin and Methylenedioxymethamphetamine (MDMA)

3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") is widely used by young people for its euphoric effects. MDMA releases serotonin (5-HT), dopamine, and norepinephrine (NE). NE release is thought to mediate the cardiovascular effects of MDMA and may also contribute to its psychostimulant effects. However, the functional role of adrenergic postsynaptic receptors in the cardiovascular and subjective effects of MDMA in humans is largely unclear. To determine the role of alpha-adrenergic receptors in the response to MDMA in humans the investigators test the effects of the alpha1-receptor blocker doxazosin on the physiological and subjective effects of MDMA. The investigators use a randomized double-blind placebo-controlled cross-over design with four experimental sessions. doxazosin or placebo will be administered before MDMA or placebo to 16 healthy volunteers. Subjective and cardiovascular responses will be repeatedly assessed throughout the experiments and plasma samples are collected for pharmacokinetics. The primary hypothesis is that doxazosin will significantly reduce the blood pressure response to MDMA.