Objectives: A variety of factors influence the incidence of placebo effects . The purpose of this study was to clarify the influence of factors such as the doctor-patient relationship, patient's motivation and expectation for drug therapy on placebo effects
Methods: Data were obtained from two double-blind randomized clinical trials with a placebo control group of 123 patients with psychosomatic disorders. The improvement was assessed by doctors at two weeks after the initiation of treatment. The doctor-patient relationship, patient's motivation and expectation for drug therapy were assessed by doctors at the beginning of clinical trials.
Results: The improvement rate in the placebo group was 42.3%, whereas the improvement rate in the diazepam group was 57.6% (p <0.05). In the placebo group, improvement rates were 50.0% in patients with a good doctor-patient relationship, 31.4% in patients with a moderate relationship and 10.0% in patients with a poor relationship (p < 0.05).Improvement rates were 46.1% in patients with a good motiva-tion for drug therapy and 19.0% in patients with poor or lack of motivation (p <0.01).Improvement rates were 36.4% in patients with low expectation for drug therapy, 53.0% in patients with a moderate one, and 7.7% in patients with high expectation (p <0.05).
Conclusion: In patients with psychosomatic disorders, factors such as the doctor-patient relationship, patient's motivation and expectation for drug therapy clearly influ-ence the incidence of placebo effects.