Heavy cannabis users develop tolerance to some impairing effects of cannabis, observable both in behavior and in brain electrical activity. In a double-blind, placebo-controlled crossover study, 12 occasional and 12 heavy cannabis users smoked a joint containing either 0 or 500 μg/kg body weight THC. During a divided attention task, THC reduced P100 amplitude in occasional users but not in heavy users, indicating tolerance at the neural level. P300 amplitude decreased in both groups. Performance on the stop signal task was impaired in both groups after THC, while divided attention task performance was impaired only in occasional users. Tolerance was evident in event-related potentials, suggesting it is not solely due to behavioral compensation.
Taking MDMA (ecstasy) during the night does not improve driving performance the next morning after sleep loss, nor does it counteract the impairing effects of sleep deprivation. In a controlled driving test, weaving (measured as standard deviation of lateral position) was significantly increased during morning drives after a night without sleep, regardless of whether participants had taken 0, 25, 50, or 100 mg of MDMA the previous evening. The degree of impairment was clinically relevant and comparable to that seen with a blood alcohol concentration above 0.8 mg/mL. MDMA cannot compensate for sleep-loss-induced driving impairment, and sleep-deprived drivers who have taken MDMA are unfit to drive.