THE EXPECTED DRUG AND ITS EXPECTED EFFECT INTERACT TO DETERMINE PLACEBO-RESPONSES TO ALCOHOL AND CAFFEINE

This study tested placebo responses in psychomotor performance when ca ffeine or alcohol was expected. Fifty male university students were as signed to one of four placebo groups or to a no-treatment control grou p. Two groups received placebo caffeine and two received placebo alcoh ol. Subjects performed 12 trials on a pursuit rotor task and performan ce was measured by the percent time on target. Then they received info rmation about the expected drug effect on the task. One caffeine place bo group (C+) and one alcohol placebo group (A+) were led to expect en hanced performance on the task. The other caffeine placebo group (C-) and alcohol placebo group (A-) were led to expect impaired performance . Subjects subsequently performed 12 trials on the task. An interactio n was obtained between the expected type of effect and the expected ty pe of drug. The CS group displayed superior performance compared to th e C- group, and the reverse relationship was observed between the A+ a nd A- group. In addition, subjects led to expect alcohol-induced impai rment (A-) performed better than subjects led to expect caffeine-induc ed impairment (C-). Subjects also reported greater motivation to resis t impairment when they expected alcohol rather than caffeine. The rese arch indicates that understanding and predicting placebo responses may require consideration of the drug that is expected as well as its exp ected effect.