Research conducted over the last number of years has clearly demonstrated that the administration of MDMA to both animals and humans has profound immunosuppressive effects, a property that it shares with other drugs of abuse.1–6 For the most part, the immunosuppressive effects of MDMA are not attributed to a direct action of the drug on immune cells, but rather to the release of endogenous immunomodulatory substances, and it is suggested that exposure to MDMA could be regarded as a ‘chemical stressor’ on the immune system. Further studies are required in order to elucidate the central and peripheral mediators of MDMA-induced immunosuppression. In addition, assessment of the effect of MDMA in preclinical host resistance models, and further clinical research, is required before any definitive statement can be made on the propensity of MDMA-induced immunosuppression to translate into increased disease susceptibility.