Conditioning and the placebo effect: The effects of decaffeinated coffee on simple reaction time in habitual coffee drinkers

An experiment is reported in which reaction time was repeatedly assessed in six subjects (habitual coffee drinkers) up to 90 min after the administration of decaffeinated coffee (i.e. placebo), 250 mg caffeine in coffee and at equivalent times on control days. As predicted reaction time was shorter (but not significantly so) immediately after the administration of the two coffee preparations. This finding was taken to support the hypothesis that through a process akin to classical conditioning, drug effects may become associated with the cues that precede and are concurrent with their administration. The findings are critically assessed and related to previous studies. Finally, it is argued that the conditioning hypothesis can account for a number of clinical findings about the placebo response as observed in therapeutic trials.