(HealthDay)—Compared with no treatment, open-label placebos seem to have a positive clinical effect, according to a review published online April 27 in the Journal of Evidence-Based Medicine.

James E.G. Charlesworth, Ph.D., from the University of Oxford in the United Kingdom, and colleagues conducted a systematic review and meta-analysis to examine the clinical efficacy of open-label placebos versus no treatment. Five , with 260 participants, met the inclusion criteria.

The clinical conditions assessed in the trials included , depression, , back pain, and attention deficit hyperactivity disorder. The researchers found that there was a moderate risk of bias in the trials. The effect of non-deceptive placebos was positive (standardized mean difference, 0.88; 95 percent confidence interval, 0.62 to 1.14; P < 0.00001; I² = 1 percent).

"Open-label placebos appear to have positive clinical effects compared to no treatment. Caution is warranted when interpreting these results due the limited number of trials identified, lack of assessor blinding, and the fact that positive messages were included alongside open-label placebos," the authors write. "Larger definitive trials are now warranted to explore the potential patient benefit of open-label placebos, to investigate the relative contributions of positive suggestions, and ethical implications."