We hypothesized that (1) symptomatic reduction of PTSD after placebo and MDMA-assisted therapy would be predicted by changes in DNA methylation on NR3C1, FKBP5, and CRHR1; and (2) MDMA-assisted therapy group would exhibit more methylation change compared to placebo, related to the additional efficacy conferred by MDMA relative to placebo conditions. The gene discussed is FKBP5; the disease is post-traumatic stress disorder.