Effectiveness of a marijuana expectancy manipulation: Piloting the balanced-placebo design for marijuana.

Abstract

Although alcohol and nicotine administration studies have demonstrated that manipulating subjects' expectancies regarding drug content affects drug response, research with marijuana has not adequately studied drug expectancy effects. The present pilot study was the first to evaluate the credibility and effect of expectancy manipulation on subjective measures and smoking patterns using a marijuana administration balanced-placebo design (BPD). In a 2 × 2 instructional set (told delta-9-tetrahydrocannabinol [THC] vs. told no THC) by drug (smoked marijuana with 2.8% THC vs. placebo) between-subjects design, the authors examined the effect of marijuana expectancy manipulation and the pharmacologic effect on affective and physiologic measures, cigarette ratings, and smoking behavior with 20 marijuana smokers (mean age = 20 years; 25% female). Large main effects of expectancy were found on ratings of cigarette potency, strength, taste, smell, and satisfaction, and observed smoking behavior. Pharmacologic effects were particularly evident for self-reported physical reactions to marijuana and cigarette potency and satisfaction ratings. This study demonstrated the feasibility of the BPD research with marijuana and yielded promising results for future studies examining the independent and combined effects of marijuana pharmacology and expectancies. Keywords marijuana; cannabis; placebo; expectancy; drug Expected effects of drugs are considered important determinants of behavioral and subjective responses to a drug independent of the pharmacological action of that drug (Vogel-Sprott & Fillmore, 1999). A drug-taking situation involves expectations that a particular drug was administered (i.e., stimulus expectancy) and expectancies about the effects or consequences associated with using the drug (i.e., outcome expectancies). The balanced-placebo design (BPD) is the optimal method for separating pharmacological effects from the cognitive expectations of receiving the drug and its effects (Marlatt & Rohsenow, 1980). This 2 × 2 Correspondence concerning this article should be addressed to Jane Metrik, Center for Alcohol and Addiction Studies, Brown University, Box G-S121-5, Providence, RI 02912. Jane_Metrik@brown.edu. NIH Public Access Author ManuscriptExp Clin Psychopharmacol. Author manuscript; available in PMC 2010 January 25. factorial design crosses the substance that is administered to the participant (drug or placebo) with instructions that are given to the participant about the drug content (drug or placebo). Thus, half of the participants are told they are receiving a drug, and half are told they are receiving no drug (i.e., instructional set manipulation). Half of the participants in each of those instructional conditions actually receive the drug and half do not. This improves on the standard placebo-controlled design by allowing a determination of expectancy effects independent of pharmacologic effects and vice versa (Rohsenow & Marlatt, 1981) and the "antiplacebo" effect of the pharmacological action of the...

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