Effect of Methylenedioxymethamphetamine (MDMA) (Serotonin Release) on Fear Extinction

Inclusion Criteria: * Male * Age between 18 and 50 years. * Understanding of the German language. * Understanding 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 coffee, black or green tea, or energy drink after midnight of the evening before the study session, as well as during the study day. * Participants must be willing not to drive a traffic vehicle or to operate machines within 48 h after substance administration. * Body mass index 18-29 kg/m2. Exclusion Criteria: * Chronic or acute medical condition * Hypertension (\>140/90 mmHg) or hypotension (SBP\<85 mmHg) * Current or previous major psychiatric disorder * Psychotic disorder in first-degree relatives * Illicit substance use (with the exception of cannabis) of more than 5 times or any time within the previous month. * Participation in another clinical trial (currently or within the last 30 days) * Use of medications that may interfere with the effects of the study medications (any psychiatric medications) * Tobacco smoking (\>10 cigarettes/day) * Consumption of alcoholic standard drinks (\>10/week or \>120 g ethanol/week)