tokens: Although 3 , 4 - methylenedioxymethamphetamine ( MDMA or ecstasy ) has been shown to damage brain serotonin ( 5 - HT ) neurons in animals and possibly humans , little is known about the long - term consequences of MDMA - induced 5 - HT neurotoxic lesions on functions in which 5 - HT is involved , such as cognitive function .