Placebo effect: impact of the expectation of caffeine on reaction time and mood

Abstract

The placebo effect is a physiological and/or psychological response to an inert substance that is believed to contain active ingredients. A body of placebo research has linked this phenomenon to the expectancy theory. The present study investigated the impact of expectations about the effects of caffeine on subjectivity (e.g., mood) and objectivity (e.g., reaction time). Subjects (n = 90) were asked to consume decaffeinated club soda and were either falsely informed that the drink contained caffeine equivalent to one cup or four cups of caffeinated coffee or were accurately told that the drink did not contain caffeine. Mood and reaction time were measured by a subjective mood scale and a lexical decision task, respectively. Results demonstrated no significant main effects or interaction effects. Although the hypotheses were not supported, the placebo effect is a highly researched occurrence and has been demonstrated in a variety of fields including pharmacology, psychology, and medicine.