Cephalalgia : an international journal of headache
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Meta Analysis
Nocebo is the enemy, not placebo. A meta-analysis of reported side effects after placebo treatment in headaches.
The aim was to determine the magnitude of the nocebo (adverse effects following placebo administration) in clinical trials for primary headache disorders. We reviewed randomized, placebo-controlled studies for migraine, tension-type headache (TTH), and cluster headache treatments published between 1998 and 2009. The frequency of nocebo was estimated by the percentage of placebo-treated patients reporting at least one adverse side effect. ⋯ For symptomatic treatment of cluster headache, the nocebo frequency was 18.67%. Nocebo is prevalent in clinical trials for primary headaches, particularly in preventive treatment studies. Dropouts due to nocebo effect may confound the interpretation of many clinical trials.