MDMA-induced CYP2D6 inhibition: concentration-dependent variability using dextromethorphan as a probe
Faezeh Ahmadi, Hoda Lavasani, Mohammadhosein Keshvadi, Youssef Daali, Mohammad Reza Rouini, Sanaz Jamshidfar, Yalda H. Ardakani
Drug Metabolism and Personalized Therapy June 16, 2026 Peer reviewed DOI: 10.1515/dmpt-2025-0029 via OpenAlex
Summary
A single dose of MDMA (ecstasy) inhibits the liver enzyme CYP2D6, but the duration of inhibition depends on the concentration of the probe drug used to measure enzyme activity. Using a therapeutic concentration of dextromethorphan (2 µM), enzyme activity was significantly reduced only at 1 hour after MDMA, with recovery by 1 week. Using a saturated concentration (300 µM), activity was reduced at 1 hour, 1 week, and 1 month. The results suggest that the apparent recovery time of CYP2D6 after MDMA exposure varies with probe concentration, likely due to differences in metabolic pathways at different substrate levels.
Study at a glance
| Design | animal study |
|---|---|
| Sample size | 32 |
| Population | rats |
| Key finding | CYP2D6 inhibition by MDMA appears prolonged when measured with a saturated concentration of dextromethorphan compared to a therapeutic concentration. |
Abstract
OBJECTIVES: Ecstasy is commonly abused due to entactogenic effects. Although our previous studies on isolated perfused rat model confirmed inhibition of CYP2D6 by MDMA, the time for enzyme recovery was different when mirtazapine and tramadol were used as substrates. Therefore, present study intended to investigate CYP2D6 inhibition by MDMA using dextromethorphan as a well-known probe. Two different concentrations of dextromethorphan were used at therapeutic and saturated level to clarify observations. METHODS: Thirty-two rats were divided into two groups (dextromethorphan concentration: 2 µM or 300 µM). Each group was divided into four subgroups. Except for control, three treatment subgroups received a single dose of MDMA (1 mg/kg) 1 h, 1 week, and 1 month before liver perfusion, respectively. RESULTS: Mean metabolic ratio using therapeutic dextromethorphan concentration showed a statistically significant decrease only in the 1-hour group compared to control. The results of the mean metabolic ratio using the saturated concentration showed a reduction in all treatment groups (p-value<0.05). CONCLUSIONS: It can be concluded that the isoenzyme behavior can be completely different using therapeutic vs. saturated probe concentrations. The best explanation for the duality observed in metabolic behavior seems to be the dependence of the metabolite on enzymatic pathway.