Goal activation, expectations, and the placebo effect.

Motivational factors receive little attention in current theories of the placebo effect. Reasons for this position are reviewed, and an argument is made for reconsidering the influence of motivation on the placebo effect. The authors hypothesize that nonconscious goals alter reactions to a placebo expectation. Specifically, the authors predict that the placebo effect is most likely to occur when individuals have a goal that can be fulfilled by confirmation of the placebo expectation. The authors tested this notion in 5 experiments. The results demonstrate the role of motivation in the placebo effect across a variety of symptom domains and via 4 different goal activation techniques. Moreover, this moderating effect occurred for both positive and negative placebo expectations, across different placebo effect measures, and in brief laboratory experiments as well as in lengthier studies. It is argued that theories regarding the placebo effect should incorporate motivational factors.