Combining MDMA and THC does not worsen cognitive impairment beyond that caused by THC alone, but it does increase the desired subjective drug effects and perceived drug strength, which may explain why many young people use them together. In a placebo-controlled crossover trial with 16 healthy volunteers aged 18–27, THC alone produced more robust cognitive impairment than MDMA alone, and co-administration did not exacerbate single-drug effects on cognitive function. However, the combination enhanced subjective experiences compared with MDMA alone.
Combining MDMA (ecstasy) with alcohol impairs psychomotor accuracy even though it increases feelings of arousal and psychomotor speed. In a double-blind, placebo-controlled crossover study with 16 healthy young adults, MDMA alone boosted speed without affecting accuracy and caused arousal, while alcohol alone slowed both speed and accuracy and induced sedation. When taken together, the combination reversed alcohol-induced sedation and improved speed, but accuracy remained significantly impaired. The effects peaked 90–150 minutes after MDMA administration and then declined, except for alcohol sedation, which emerged fully after the infusion stopped. This mismatch between perceived performance and actual impairment may affect neuropsychological functioning.