The goal of this clinical trial is to learn if MDMA impacts startle response in healthy participants. The main question it aims to answer is: Does MDMA impact participant's performance on a startle test? Researchers will compare healthy volunteers who have taken MDMA to those who have taken placebo. Participants will first undergo a 1-hour startle test. The next day, they will be randomized to receive either MDMA or placebo followed by another startle test and vitals signs and blood measurements. Participants will return the next day for a final startle test. Their sleep will be tracked by a Fitbit device.

This is a randomized, blinded, placebo-controlled Phase 1 study that aims to evaluate the impact of 3,4-methylenedioxymethamphetamine (MDMA) on startle response. This study will enroll healthy participants. At Visit 1, all participants will undergo a 1-hour startle test. Acoustic startle will be measured through assessing eye-blink response from the orbicularis oculi muscles in response to a 106 dB noise, using sensors under the eye. While watching the computer monitor, the participant will also experience several brief blasts of air directed at the throat. At Visit 2 (24 hours later), participants will be randomized to receive 100 mg of MDMA or inactive placebo, after which they will undergo another startle test. Participants enrolled in the study who agree to do this will have their blood drawn to measure levels of oxytocin, and possibly other hormones or proteins, such as cortisol or brain-derived neurotrophic factor (BDNF). Measuring oxytocin will be blind to condition, and the decision will happen before randomization to either condition. Blood will be drawn before MDMA or placebo administration, and eight times afterwards.The researchers will measure pulse, blood pressure and temperature once before and six times after receiving MDMA or placebo, and study participants will complete a questionnaire about their experience. At Visit 3, participants will return for a final startle test and recall task. Sleep will be measured via self-report and Fitbit during study participation.