Correlates of Anxiety Associated With a Life-threatening Illness

The goal of this observational trial is to gather brain scan data on people undergoing MDMA-assisted therapy. The main question it aims to answer is: -How does brain activity change while completing an emotional regulation task in participants receiving MDMA-assisted therapy? Researchers will compare participants receiving MDMA-assisted therapy to participants receiving placebo plus therapy. Participants will undergo baseline brain scans with functional magnetic imaging (fMRI) while they perform an emotional regulation task and other attentional tasks. Participants will then undergo two medication sessions of MDMA or placebo-assisted therapy. Then, undergo another brain scan. Participants will then undergo a third medication session and repeat the brain scans.