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The purpose of this study was to assess the efficacy of botulinum toxin in reducing the frequency of migraine headaches.The MEDLINE, Embase, and Cochrane Library databases were searched to identify randomized, double-blind, placebo-controlled trials that compared patients receiving botulinum toxin versus placebo injections in the head and neck muscles, for the preventive treatment of migraine. The primary outcome was change in the number of headache episodes per month from baseline to 3 months.There were 17 studies including a total of 3646 patients. Overall analysis reported a tendency in favor of botulinum toxin over placebo at 3 months, with a mean difference in the change of migraine frequency of −0.23 (95 percent CI, −0.47 to 0.02; p = 0.08). The reduction in frequency of chronic migraines was significant, with a mean differential change of −1.56 (95 percent CI, −3.05 to −0.07; p = 0.04). Analysis of chronic migraine frequency was also significant after 2 months. The findings also highlighted an improvement of the patient’s quality of life at 3 months in the botulinum toxin group (p < 0.00001). Further adverse events were traced in the botulinum toxin type A group with a statistically significant risk ratio of 1.32 (p = 0.002).This meta-analysis reveals that botulinum toxin type A injections are superior to placebo for chronic migraines after 3 months of therapy. For the first time, a real benefit in patient quality of life is demonstrated with only few and mild adverse events.Therapeutic, II.