The role of expectations in predicting pain response in a repeated placebo design

Placebos are often used effectively in clinical practice to relieve pain, and experimental pain studies have implicated patients' expectations for pain relief in eliciting a placebo response. Previous studies in our laboratory have shown that knowledge of having received a placebo does not significantly inhibit a second placebo response, nor does it affect participants' mood or attitudes about treatment. The role of participants' expectations in their subsequent pain response following repeated placebo administration is currently unknown. We examined 41 healthy individuals (16 male, 25 female) who completed 3 thermal pain trials and experienced repeated placebo-related analgesia in 2 consecutive trials. Following the baseline measurement of their pain response, verbal suggestion and conditioning procedures were used to elicit a placebo response. All participants reported their expectations for pain intensity prior to each of the three pain trials (baseline measurement, first placebo trial, and second placebo trial). Results identified a significant relationship between testing trial and pain rating [F(1,40) = 127.78, p.05, ηp2 = .05], indicating highly similar response patterns between expectancy and subsequent reports of pain intensity. These findings suggest that expectation for pain is an important factor in initial and repeated placebo responding. (Supported by NIH Grant RO1 AT001424.) Placebos are often used effectively in clinical practice to relieve pain, and experimental pain studies have implicated patients' expectations for pain relief in eliciting a placebo response. Previous studies in our laboratory have shown that knowledge of having received a placebo does not significantly inhibit a second placebo response, nor does it affect participants' mood or attitudes about treatment. The role of participants' expectations in their subsequent pain response following repeated placebo administration is currently unknown. We examined 41 healthy individuals (16 male, 25 female) who completed 3 thermal pain trials and experienced repeated placebo-related analgesia in 2 consecutive trials. Following the baseline measurement of their pain response, verbal suggestion and conditioning procedures were used to elicit a placebo response. All participants reported their expectations for pain intensity prior to each of the three pain trials (baseline measurement, first placebo trial, and second placebo trial). Results identified a significant relationship between testing trial and pain rating [F(1,40) = 127.78, p.05, ηp2 = .05], indicating highly similar response patterns between expectancy and subsequent reports of pain intensity. These findings suggest that expectation for pain is an important factor in initial and repeated placebo responding. (Supported by NIH Grant RO1 AT001424.)