Regulation of the self-administration of marihuana by psychological and pharmacological variables

Although psychosocial variables affect the consequences of marihuana ingestion, little is known of the role of such variables as determinants of the self-administration of the drug. To pursue this question, three variables were manipulated in a factorial design. Marihuana use history was manipulated by selecting subjects at extremes of use frequency. To determine the possible contribution of learned smoking habits to consumption, subjects smoked either large or small cigarettes. Finally, cigarettes varying in concentration of delta-9 tetrahydrocannabinol (0.36%, 0.73% or 1.45%) were used. Subjects were simply asked to smoke until they had attained a “nice high”. Although there was some evidence of titration according to potency, subjects self-administrated more total tetrahydrocannabinol the more potent the material in attaining the same subjective endpoint of intoxication. More material was ingested in the form of large than small cigarettes. The latter variable accounted for nearly as much variance as did drug potency itself. This result illustrated the importance of an essentially cognitive variable as a determinant of drug intake. Finally, there was no difference in the amount required by frequent and infrequent users to attain the intoxication criterion. The latter result was in opposition to the assertion by Nahas (1973) that frequent exposure to cannabis will ultimately result in an increase in the amount required to produce the reinforcing effects of marihuana. It was emphasized that assertions about the contribution of various factors to drug-taking behavior should be withheld in the absence of data from experiments in which actual self-administration is the dependent variable.