The cognitive theory states that patient expectations are critical in the placebo response. The administration of a placebo creates an expectation of a certain response, and the expectation of this response creates a biological effect. The mechanisms whereby expectancies might produce biological effects are many. They include (1) a reduction in anxiety which could aid immune system functioning, (2) changes in cognition or coping mechanisms, or (3) changes in behavior that would improve health outcomes (Stewart-Williams and Podd 2004). Patient expectations can be quite specific, and studies have shown that expectations of pain relief in particular body parts lead to the expected effect in that body part alone (Benedetti et al. 1999, Montgomery and Kirsch 1996).
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