Reviewed by: HU Medical Review Board | Reviewed April 2022 | Last updated: May 2023

Botox: Quick Look

UsePrevent migraine in people with chronic migraines
EffectivenessProven efficacy in chronic migraine1
Migraine-specific?No, but FDA approved for migraine prevention
Side effectsNeck pain, muscular weakness
Taken how?Injection
Drugs in this class
Brand NameGeneric Name
Botoxonabotulinumtoxin A

Botox® (onabotulinumtoxin A) is an injectable preventive treatment. It is approved to treat people with chronic migraine.2 Chronic migraine is defined as 15+ days per month with headache lasting at least 4 hours a day or longer.

Botox is a well-studied neurotoxin that has been used for over 30 years.3 Botox was first used to treat eye alignment problems, relieve neck spasms, reduce wrinkles, and stop excessive sweating.2 People using Botox for these reasons noticed that their migraine had also improved.4

Botox for chronic migraine

Large clinical trials were done to study whether Botox prevented migraine. The results showed that Botox reduced headache and migraine days.5,6 Based on these results, the FDA approved Botox for chronic migraine prevention in 2010.2 Botox does not work for people with episodic migraine.

Botox works by binding to certain areas, known as receptors, on nerves and muscle fibers. This blocks the release of specific brain chemicals, including acetylcholine. This, in turn, blocks muscle activity.2 It is not completely known how Botox reduces headache pain and stiffness. A potential reason might be that Botox blocks nerves that send pain messages to the brain and relaxes muscles so they are less sensitive to pain.

Botox is injected into the muscles of the neck and face by a doctor. There are 31 injection sites. It is given every 12 weeks. Some patients see results at week 4. It may take up to two treatment cycles to achieve maximum benefit.7

Many insurance companies require that people with chronic migraine try other preventive medications first before they will cover Botox for migraine prevention.8

How well does Botox work?

Botox was studied for migraine prevention in the PREEMPT 1 and 2 trials.5,6 Each trial had around 700 participants with chronic migraine. Participants had about 20 headache days per month. Two-thirds of participants were using acute (or abortive) medications often.

For the first two treatments, half of the participants were treated with Botox, the other half got placebo. Then everyone got 3 more treatments with Botox.

The results showed that people treated with Botox had about 8 to 9 fewer migraine and headache days per 28 days.5-7 Interestingly, people in the placebo group also improved. They had about 6 to 7 fewer migraine and headache days. The fact that Botox helped more was unlikely to be due to chance.

What are the possible side effects of Botox?

Side effects were rare and mostly mild in the two large clinical trials of Botox.5,6 The most common side effects of Botox were:4

  • Neck pain (4.3 percent)
  • Temporary droopy eyelids or eyebrows (1.9 percent)
  • Muscular weakness (1.6 percent)

Do not drive if you experience weakness, blurry vision, or drooping eyelids after treatment with Botox.2

You should not take this medication if you are allergic to it or have a skin infection at the injection site. This medication is not approved for children.

Seek immediate medical attention if you experience problems breathing or swallowing, or if you have signs of allergy, including swelling in the face, throat, lips, or tongue.

Botox has a black box warning—the FDA’s strongest warning—about the possible distant spread of the toxin effects.2 In rare cases, the paralyzing effect of Botox has spread to other areas of the body. This can lead to problems breathing or swallowing. This effect did not occur in either trial of Botox for migraine.5,6

This is not an exhaustive list of all potential side effects of Botox. For more information, consult your doctor or healthcare provider. If you notice any new or worsening side effects, contact your doctor or healthcare provider immediately. You should begin no medication or supplement without first checking with your health care provider and should let them know of any other prescriptions, OTCs, and herbals you are taking to ensure there are no interactions.

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