Headache: the placebo effects in the control groups in randomized clinical trials; an analysis of systematic reviews.

Objective: The purpose of this study is to describe the effects in the placebo and "no treatment" arms in trials with headache patients. Method: This is a secondary analysis of randomized controlled trials from 8 systematic reviews and selected trials with a "no treatment" or placebo control group. The different types of "no treatment" and placebo interventions were assessed and classified into 6 subgroups. The analyses were carried out according to type of outcome variable. Results: In total, 119 studies were included (7119 participants). The mean recovery rate in all control groups was 35.7%. Significantly more participants recovered in control groups of pharmacological studies than in nonpharmacological studies: 38.5% vs 15.0%, respectively. Adults were more likely to recover in nonpharmacological studies and children in pharmacological studies. Conclusions: The mean recovery rate in the control groups was 36%. The recovery rate varied substantially between type of intervention and patients. © 2011 National University of Health Sciences.