Placebo effects on itch: a meta-analysis of clinical trials of patients with dermatological conditions.

Although placebo contributes to the effects of treatment for various symptoms and conditions, its effect on itch has rarely been investigated. In this meta-analysis, the magnitude of the placebo effect on itch was systematically investigated in clinical trials including patients with chronic itch due to atopic dermatitis, psoriasis, or chronic idiopathic urticaria. From searches in four databases, 34 articles were included in the quantitative analyses. Placebo treatment significantly decreased itch (1.3 out of 10, 95% confidence interval 1.02-1.61) compared with baseline itch (effect size 0.55), indicating that placebo effects have a considerable role in these patients' treatment.