Prediction of MDMA response in healthy humans: a pooled analysis of placebo-controlled studies

3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") is used both recreationally and therapeutically. Little is known about the factors influencing inter- and intra-individual differences in the acute response to MDMA. Effects of other psychoactive substances have been shown to be critically influenced by personality traits and mood state before intake.; We pooled data from 10 randomized, double-blind, placebo-controlled, cross-over studies performed in the same laboratory in 194 healthy subjects receiving doses of 75 or 125mg of MDMA. We investigated the influence of drug dose, body weight, sex, age, drug pre-experience, genetics, personality and mental state before drug intake on the acute physiological and psychological response to MDMA.; In univariable analyses, the MDMA plasma concentration was the strongest predictor for most outcome variables. When adjusting for dose per body weight, we found that (a) a higher activity of the enzyme CYP2D6 predicted lower MDMA plasma concentration, (b) a higher score in the personality trait "openness to experience" predicted more perceived "closeness", a stronger decrease in "general inactivation", and higher scores in the 5D-ASC (5 Dimensions of Altered States of Consciousness Questionnaire) scales "oceanic boundlessness" and "visionary restructuralization", and (c) subjects with high "neuroticism" or trait anxiety were more likely to have unpleasant and/or anxious reactions.; Although MDMA plasma concentration was the strongest predictor, several personality traits and mood state variables additionally explained variance in the response to MDMA. The results confirm that both pharmacological and non-pharmacological variables influence the response to MDMA. These findings may be relevant for the therapeutic use of MDMA.