Findings include the following:

• In five studies of chronic migraine (1508 patients; mean, 19.5 headaches monthly), botulinum toxin A significantly reduced the average number of headaches by 2.3 per month compared to placebo; the average monthly reduction in headaches was roughly 8 with botulinum and 6 with placebo.
• In seven studies of chronic tension headache (675 patients, mean, 25.2 headaches monthly), botulinum toxin A did not significantly reduce the average number of headaches compared to placebo.
• In nine studies of episodic migraine (1838 patients; mean, <15 headaches monthly), botulinum toxin A did not significantly reduce the average number of headaches compared to placebo.
• In the few studies that examined the proportion of patients experiencing 50% improvement in headache, botulinum was superior to placebo for chronic migraine; however, these trials included fewer than 100 patients.
• Adverse effects — especially ptosis, muscle weakness, and neck pain — were significantly more common with botulinum than with placebo.

Comment

For prophylaxis against chronic migraine, the average benefit for botulinum toxin A compared to placebo is statistically significant but clinically modest; the placebo effect is impressive in this study. Moreover, treatment is costly (up to several thousand dollars yearly), and side effects are frequent; hence, this intervention will not be worthwhile for most people.