Operant acquisition of marihuana in man.

Operant work for marihuana cigarettes or money and the effects of marihuana smoking on behavior were examined in 12 casual and 15 heavy marihuana users. Male volunteers were studied in groups of four on a clinical research ward and each subject served as his own control. A 5-day base-line period was followed by a 21-day marihuana available period and a 5-day postmarihuana control period. Subjects could earn one 1-g marihuana cigarette or 50 cents by 30 minutes of sustained performance on a simple operant task. All casual and most heavy user subjects gradually increased marihuana smoking through time. The heavy users smoked more (4.3-6 cigarettes/day) than the casual users (2-3/day). Both groups worked between 2 and 5 times as many hours per day as was necessary to earn the number of cigarettes smoked. Consequently, subjects earned and saved far more money than was spent for marihuana. The heaviest smokers worked between 6.7 and 14.4 hours/day, every day. Periods of maximal work coincided with periods of maximal smoking, i.e., between 4 P.M. and 12 midnight each day. Delayed effects of marihuana dose on points earned the following day showed a dose-related decrement in operant work output. In the heavy user group, operant performance decreased sharply 24 hours after 3 ciagrettes/day were smoked, then remained relatively stable after 3 to 8 cigarettes daily and decreased further on the few occasions when more than 8 cigarettes were smoked. In the casual user group, the largest 24-hour delayed changes in performance occurred after the smoking of between 1 and 2 and 3 and 4 marihuana cigarettes. No subject stopped operant work even when he smoked 10 or more marihuana cigarettes per day. These data do not support the hypothesis that marihuana induces an "amotivational" syndrome.