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Effects of Expectancies on Subjective Responses to Oral Δ9-Tetrahydrocannabinol

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Abstract

The effects of expectancies on subjective responses to oral Δ9-tetrahydrocannabinol (Δ9-THC) were examined. Thirty-five regular marijuana users were assigned to one of two groups: one group was told that they may receive a cannabinoid or placebo and a second group was told that they may receive a drug from one of several classes of drugs (e.g., stimulant, sedative, antiemetic) or placebo. Regardless of the group to which they were assigned, subjects received each of two oral doses of Δ9-THC (7.5 and 15 mg) and placebo, one dose per session, for a total of three sessions. Measures of subjective effects, including visual analog scales and the Addiction Research Center Inventory (ARCI), were administered at 0.5-h intervals throughout each session. Consistent with previous research using other drugs, subjects in the current experiment who expected to receive a cannabinoid reported greater pleasurable effects than subjects who did not have this expectancy. The results have implications for understanding the effects of cannabinoids when used in both recreational and clinical settings.

Section snippets

Subjects

Thirty-five healthy male (n = 19) and female (n = 16) volunteers [mean age (SD) = 23.5(4.3)] participated. The majority of subjects were Caucasian, single, undergraduate college students who were of normal weight. Table 1 summarizes the demographics and drug use histories of both subject groups. To be included in the experiment, subjects had to report (a) use of marijuana for at least 1 year, (b) use of marijuana at least 10 times in their lifetime, and (c) use of marijuana within the past 2

Results

Dependent measures were analyzed using separate three-way (dose × hour × group) mixed-factor analyses of variance (ANOVAs). For tests of within-subjects effects, Huynh-Feldt corrections were used to protect against violations of sphericity. The criterion for statistical significance was set at p < 0.05. Table 2 shows significant main effects and interactions for all dependent measures.

Discussion

As hypothesized, subjects who were told that they would receive a cannabinoid reported higher ratings on certain measures of subjective drug effects when they received oral Δ9-THC. Specifically, the informed group reported higher ratings on visual analog scales of “like” effects and “want more” drug, higher scores on the ARCI’s MBG scale, which measures euphoria, and a greater desire to take the drug again. Interestingly, the instructional conditions did not affect other qualitative measures of

Acknowledgements

This research was supported by National Institute on Drug Abuse Grants DA 03517 and T32 DA 07255. The authors thank Jeff Stolte for his assistance with the study.

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