'Hangover' effects the morning after marijuana smoking.

Thirteen male marijuana smokers participated in a study to determine whether marijuana smoked in the evening would result in measurable subjective or other behavioral effects the following morning. Subjects smoked either active (2.9% delta 9THC) or placebo (0.0% delta 9THC) marijuana cigarettes according to a standardized smoking regimen. Smoke inhalation was monitored by measuring expired air carbon monoxide (CO) levels before and after smoking. Acutely, active marijuana produced significant changes in heart rate, CO level, various measures of subjective effects, and behavioral tasks of card sorting, free recall and time production. When the test battery was repeated the following morning (approx. 9 h after smoking), significant changes were observed on two subjective effects scales and on the time production task after active, but not placebo, marijuana. These apparent 'hangover' effects were different from the acute effects of marijuana. The findings suggest that marijuana smoking can produce residual (hangover) effects the day after smoking. The precise nature and extent of these effects, as well as their practical implications, remain to be determined.