Smoked marijuana effects on tobacco cigarette smoking behavior.

The effects of marijuana smoke exposure on several measures of tobacco cigarette smoking behavior were examined. Eight healthy adult male volunteers, who smoked both tobacco and marijuana cigarettes, participated in residential studies, lasting 10 to 15 days, designed to measure the effects of marijuana smoke exposure on a range of behavioral variables. Tobacco cigarettes were available throughout the day (9:00 A.M. until midnight). Each day was divided into a private period (9:00 A.M. to 5:00 P.M.), during which subjects were socially isolated, and a social period (5:00 P.M. to midnight), during which subjects could interact. Under blind conditions, subjects smoked placebo and active marijuana cigarettes (0%, 1.3%, 2.3%, or 2.7% delta 9-tetrahydrocannabinol) four times daily (9:45 A.M., 1:30 P.M., 5:00 P.M. and 8:30 P.M.). Each subject was exposed to both placebo and one active dose over 2- to 5-consecutive-day intervals, and dose conditions (i.e., placebo or active) alternated throughout the study. Active marijuana smoking significantly decreased the number of daily tobacco smoking bouts, increased inter-bout intervals and decreased inter-puff intervals. Marijuana decreased the number of tobacco smoking bouts by delaying the initiation of tobacco cigarette smoking immediately after marijuana smoking, whereas decreases in inter-puff intervals were unrelated to the time of marijuana smoking. No consistent interactions between marijuana effects and social or private periods (i.e., time of day) were observed.