Pharmacological Interaction Between Clonidine and Methylenedioxymethamphetamine (MDMA)

Inclusion Criteria: * Sufficient understanding of the German language * Subjects understand the procedures and the risks associated with the study * Participants must be willing to adhere to the protocol and sign the consent form * Participants must be willing to refrain from taking illicit psychoactive substances during the study. * Participants must be willing to drink only alcohol-free liquids and no xanthine-containing liquids (such as coffee, black or green tea, red bull, chocolate) after midnight of the evening before the study session. Subjects must agree not to smoke tobacco for 1 h before and 4 hours after MDMA administration. * Participants must be willing not to drive a traffic vehicle in the evening of the study day. * Women of childbearing potential must have a negative pregnancy test at the beginning of the study and must agree to use an effective form of birth control. Pregnancy tests are repeated before each study session. * Body mass index: 18-25 kg/m2 Exclusion Criteria: * Chronic or acute medical condition including clinically relevant abnormality in physical exam, laboratory values, or ECG. In particular: Hypertension (\>140/90 mmHg). Personal or first-grade history of seizures. Cardiac or neurological disorder. * Current or previous psychotic or affective disorder * Psychotic or affective disorder in first-degree relatives * Prior illicit drug use (except THC (Tetrahydrocannabinol)-containing products) more than 5 times or any time within the previous 2 months. * Pregnant or nursing women. * Participation in another clinical trial (currently or within the last 30 days) * Use of medications that are contraindicated or otherwise interfere with the effects of the study medications (monoamine oxidase inhibitors, antidepressants, sedatives etc.)