There is increasing evidence that new interventional pharmacotherapies such as psychedelic therapy may be helpful for the treatment of a number of mental health conditions. The purpose of this study is to explore the potential for psychedelic therapy using psilocybin and MDMA to improve symptoms of treatment resistant OCD, and to determine whether there is any pre-post change in electroencephalography (EEG) measurements following psychedelic exposure. To do so, we are conducting a double-blind (participant and rater) clinical trial where participants with treatment resistant OCD will undergo psilocybin or MDMA assisted psychotherapy including a series of preparation and integration therapy sessions, and 3 drug administration sessions. The results of this study will provide us information about the effectiveness, acceptability, and tolerability of this treatment for this disorder, as well as whether there are any brain activity changes associated with having been exposed to MDMA and psilocybin.