The reinforcing, self-reported performance and physiological effects of Δ9-tetrahydrocannabinol, triazolam, hydromorphone, and methylphenidate in cannabis users

The use of illicit prescription drugs is common in cannabis users; however, the effects of few psychoactive drugs have been characterized in this population. In this study, Δ-tetrahydrocannabinol (i.e. Δ-THC), triazolam, hydromorphone, and methylphenidate were administered to cannabis users (n=8). Subjects completed the multiple-choice procedure to assess drug reinforcement, as well as self-report questionnaires and performance tasks; physiological assessments were also conducted. Only Δ-THC increased the crossover point on the multiple-choice procedure, but all of the drugs increased ratings on one or more 'positive' drug-effect questionnaire items, as well as items specific for each drug. Triazolam produced the most robust performance impairment, except on a time reproduction task, which was impacted to a greater degree by Δ-THC. Δ-THC elevated heart rate and decreased temperature, triazolam increased heart rate, methylphenidate elevated all cardiovascular indices, and hydromorphone reduced respiration. The effects of the drugs tested in this study were generally consistent with their known pharmacology, although minimal responses to hydromorphone were observed. Future research to directly compare the effects of different psychoactive drugs in cannabis users and nonusers would be useful for identifying potential differences in drug effects as a function of use history.