Marijuana smoking: Effect of varying Δ⁹-tetrahydrocannabinol content and number of puffs

The purpose of this study was to determine marijuana dose-effects on subjective and performance measures over a wider dosage range than previously reported using technology which allowed for specification of both the volume and Δ⁹-tetrahydrocannabinol (THC) content of smoke delivered, and to relate these effects to plasma THC levels. Seven male community volunteers, who were moderate users of marijuana, smoked 4, 10 or 25 puffs from cigarettes containing either 1.75 or 3.55% THC on 6 separate days. Postsmoking plasma THC levels were systematically related to both number of puffs and cigarette THC content. Maximal THC levels occurred immediately after smoking and ranged from 57 to 268 ng/ml. These plasma levels provided a measure of systemic delivery when a known volume and THC content of marijuana smoke was inhaled. Orderly dose-related increases were also observed for heart rate, expired air carbon monoxide and subjective report of drug effects. The 25-puff, 3.55%-THC condition produced greater plasma THC levels than previously reported and reliably impaired performance on a battery of psychomotor and cognitive tasks with substantial individual differences noted in the degree of performance impairment. Puff number/THC content combinations producing comparable plasma THC levels resulted in similar subjective effects and performance impairment. This study provided a comprehensive assessment of the pharmacological effects of smoked marijuana over a wider and more precisely controlled dosage range than has been accomplished previously. The study showed that subjective measures were more sensitive to marijuana effects than were performance measures at mean plasma THC levels of 170 ng/ml or lower and that large individual differences in extent of performance impairment were apparent at higher plasma THC levels.