Paroxetine increases blood levels of MDMA

In Clin. Pharmacokinet., 2005, 44(6), 649-660 de la Torre et al gave the antidepressive drug paroxetine (Paxil and other trade names) prior to MDMA consumption. Paroxetine inhibits the CYP2D6 enzyme which is responsible for MDMA metabolism. The authors conclude that CYP2D6 is responsible for less than 30% of the MDMA metabolism.
The combination of paroxetine and MDMA increased the total blood level (AUC) of MDMA and increased the maximum concentration (cmax) while decreasing the amount of the primary metabolite HMMA. The time until the maximum concentration (tmax) is not changed. The elimination of MDMA (ke) is decreased compared to MDMA and placebo.
The authors conclude that CYP2D6 polymorphism is less likely to be linked to MDMA toxicity as MDMA is still metabolised to HMMA by other, unknown enzymes.