MDMA-AT for PTSD in Young Adults With Childhood Trauma

This study is testing a new, emerging treatment for young adults (ages 18-26) with Posttraumatic Stress Disorder (PTSD). The treatment is combining the substance, MDMA, with up to three psychotherapy sessions, also known as MDMA-Assisted Therapy (MDMA-AT). The main questions it aims to answer are: * Is the treatment safe and feasible to administer? * Does the treatment improve PTSD symptoms? Participants will be asked to: * Complete screening procedures, including a medical and psychiatric evaluation to ensure safe participation * Attend up to three preparatory talk therapy sessions prior to the first MDMA-AT dosing session * Attend three integration talk therapy sessions after each MDMA-AT dosing session * Attend up to three total MDMA-AT dosing sessions * Complete assessments from baseline to 38-weeks post-baseline * Complete a fMRI scan at baseline and at 18-weeks post-treatment * Complete self-report measures and ecological momentary assessments (EMAs) across the study period