Disentangling expectancy effects from pharmacological effects using caffeine performance as a model

Beliefs about the effects of drugs, or drug outcome expectancies, have been shown to modify the effects of drugs and placebos. In other words, cognitive and pharmacological effects both appear to be involved in the drug experience. This study investigated the independent and interactive effects of caffeine and instructional set on subjective and performance outcomes. Regular coffee drinkers (N = 60) were asked to abstain from caffeine overnight for at least 15 hours and were then randomly assigned to receive either caffeinated or decaffeinated coffee under double-blind conditions. This was crossed with varying instructions to participants that the coffee would either enhance or impair performance in a 2 X 2 factorial design. Even though a main effect for dose demonstrated that participants who received decaffeinated coffee demonstrated worse performance than those who received caffeinated coffee, among those given decaf, those told to expect impairment from coffee performed better than those told to expect enhancement. These findings add further support to the idea that drug expectancies play a role in drug outcomes.