3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") is widely used by young people for its euphoric effects. MDMA releases serotonin (5-HT), dopamine (DA), and norepinephrine (NE). 5-HT release mainly contributes to the subjective effects of MDMA whereas NE release is involved in the cardiovascular and psychostimulant effects of MDMA. DA is also likely to be involved in the rewarding and reinforcing effects of drugs of abuse. However, the functional role of DA in the subjective effects of MDMA in humans is largely unclear. To determine the role of the DA transporter (DAT) in the response to MDMA in humans the investigators test the effects of the DA and NE transporter blocker methylphenidate on the subjective effects of MDMA. The investigators use a randomized double-blind placebo-controlled cross-over design with four experimental sessions. methylphenidate 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 methylphenidate will significantly reduce the subjective effects of MDMA.