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Am Fam Physician. 2020;101(3):144-145

Author disclosure: No relevant financial affiliations.

Clinical Question

Is onabotulinumtoxinA (Botox) safe and effective at reducing the frequency of chronic migraine headaches in adults?

Evidence-Based Answer

OnabotulinumtoxinA reduces the number of migraine days per month by two days compared with placebo in adults with chronic migraines. Nonserious adverse effects are more common in patients treated with onabotulinumtoxinA (number needed to harm [NNH] = 7; 95% CI, 4 to 17) than adverse effects overall (NNH = 7; 95% CI, 6 to 9).1 (Strength of Recommendation: A, based on consistent, good-quality patient-oriented evidence.)

Practice Pointers

Chronic migraine is defined as 15 or more headache days per month, with at least eight of those headaches being a migraine. In the United States, 26.2% of patients with chronic migraine vs. 13.9% of patients with episodic migraine (i.e., zero to 14 headache days per month) reported visiting a primary care physician in the preceding three months (P < .001).2 Many have frequent attacks despite available treatments and find themselves dependent on long-term opiate or barbiturate therapy. Although onabotulinumtoxinA is approved by the U.S. Food and Drug Administration for the treatment of chronic migraine, its effectiveness in the prevention of chronic migraine had not been evaluated previously.

This Cochrane review included 28 clinical trials (21 of which had fewer than 50 participants each) involving 4,190 participants who were an average age of 42 years.1 One-half of participants had chronic migraines, and 80% were female. Most of the trials lasted only a few months. The treatment regimen (dosage, timing, and exact placement of injections) of onabotulinumtoxinA varied across studies. Twenty-three trials compared onabotulinumtoxinA with placebo. Sixteen trials, which involved 80% of participants, were industry funded.

OnabotulinumtoxinA reduced the number of migraine days per month by 3.1 days in patients with chronic migraine (95% CI, 1.4 to 4.7; four trials; 1,497 participants; low-quality evidence). This dropped to two days (95% CI, 1.1 to 2.8; two trials; 1,384 participants; moderate-quality evidence) when excluding the smaller trials because of concerns about bias and inadequate follow-up. No serious adverse effects were noted. Reporting of nonserious adverse effects varied between trials; however, blepharoptosis, arm muscle weakness, neck pain, and injection site pain were more common in participants who received treatment than in those who received placebo (60% vs. 47%; NNH = 7; 95% CI, 4 to 17).

The National Institute for Health and Care Excellence and the Institute for Clinical Systems Improvement published a guideline on the use of onabotulinumtoxinA to prevent chronic migraines in adults.3 The guideline recommends onabotulinumtoxinA as an option for the prophylaxis of headaches in adults with chronic migraine provided the headaches have not responded to at least three previous pharmacologic prophylaxis therapies and for whom medication overuse has been appropriately managed.

The practice recommendations in this activity are available at

These are summaries of reviews from the Cochrane Library.

This series is coordinated by Corey D. Fogleman, MD, assistant medical editor.

A collection of Cochrane for Clinicians published in AFP is available at

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