Rapid Effects of MDMA Administration on Self-Reported Personality Traits and Affect State: A Randomized, Placebo-Controlled Trial in Healthy Adults

3,4-methylenedioxymethamphetamine (MDMA) assisted therapy has been shown to be a safe and effective treatment for PTSD and emerging research suggests a change in personality traits may be a factor in treatment response. Most prior research on MDMA and personality has focused on cross-sectional comparisons of MDMA users and non-users; as such, well-controlled research assessing personality and affective states <i>change</i> following MDMA vs placebo administration is needed. In the current pre-registered study, we investigated the impact of MDMA administration on five-factor model (FFM) traits and affective states before and 48 h after drug administration in a randomized, placebo-controlled study of healthy adults (<i>N</i> = 34). Statistical significance was not observed for the four a priori hypotheses; however, medium effect sizes were found between MDMA administration and trait Openness and Positive Affect 48 h following drug administration, compared to placebo (<i>d</i> = .79 and .51, respectively). This study provides initial results to help guide future well-powered studies with large samples and longer follow-up timepoints to continue to investigate how MDMA impacts personality and emotional experience, which may inform optimization of MDMA treatment approaches.