The placebo effect and homeopathy.

BACKGROUND: Like other forms of medicine, including Complementary and Alternative Medicine (CAM), homeopathy elicits expectations in patients. The physician-patient relationship, personal and comprehensive treatment and lack of adverse effects are elements in creating positive expectations. Other elements may be associated with negative expectations. METHODS: We conducted a systematic literature review on placebo and nocebo effects in acupuncture and homeopathy using Medline. RESULTS: Findings on the psychophysiological and neuromediating mechanisms of the placebo-nocebo phenomenon are reviewed. Studies of these effects reveal how expectations and unconscious conditioning can be measured by imaging and EEG methods. They result in significant, non-specific therapeutic effects, which may confuse the evaluation of the specific therapeutic effects treatment, hampering selection of the simillimum. CONCLUSIONS: Directions for future research on non-specific therapeutic effects of homeopathy to improve clinical practice and clinical research are discussed.