Effects of smoked marijuana on heart rate, drug ratings and task performance by humans.

Six subjects, reporting marijuana use between two and 30 times per month, participated in studies of the acute effects of smoked marijuana (0.0%, 2.0% and 3.5% Delta(9)-THC, w/w) on heart rate, ratings of drug effect and task performance. Marijuana was administered using a uniform-puffing procedure with monetary contingencies associated with puff and breathhold duration. In general, heart rate and ratings, of "High" and dose "Potency" were increased by marijuana, and performance on some tasks was altered by drug administration. The relative sensitivity of the measures varied across subjects, and no single measure, such as heart rate or verbal rating of drug effect, could be used to predict the behavioral effects of marijuana. Marijuana puff durations were decreased at the highest dose, but dose-related changes in heart rate and task performance indicated that the change in smoking topography did not result in complete compensation for increased cannabinoid concentrations in marijuana smoke.