DEAR MAYO CLINIC: I have suffered with migraines on and off for about five years. Recently, the oral therapy I've used seems to be less effective. While I know newer medications are available, a friend suggested I try Botox injections. She swears it brought her chronic headaches under control. How safe are these injections, and how does Botox work? What is the treatment schedule, and would I also need to be on other headache medication, too?

ANSWER: Onabotulinum toxin A, or Botox, was approved by the Food and Drug Administration in 2010 to treat chronic migraine headaches. It is not a cure. People who receive Botox injections for headaches usually get the treatment about every three months.

For some, that is all they need to keep their headaches under control. For others, additional medication or other headache therapy is necessary. Research is ongoing about new forms of migraine therapy.

Botox is a medication that uses a form of botulinum toxin to temporarily paralyze muscle activity. Best known for its ability to reduce the appearance of facial wrinkles, Botox also has been shown to prevent chronic migraine headaches in some people. It is used mainly for those who have headaches 15 or more days per month.

Since 2002, doctors at Mayo Clinic have treated thousands of patients with chronic migraine effectively and safely using Botox. The medication typically is injected into muscles of the forehead, scalp, neck and shoulders.

The specific details of how Botox works to prevent headaches are not known. But it is likely that the injected Botox is taken up by pain receptors in the muscles' nerves. The medication then deactivates those pain receptors and blocks pain signals that the nerves send to the brain.

The pain does not go away permanently, however. After several months, the nerves sprout new pain fibers, and the headaches tend to return. The Botox effect usually lasts about 2½ months. Because injections are repeated no sooner than every three months, some people need other headache treatments for the last two weeks of a Botox cycle.

Providing Botox treatment for headaches every three months is a national standard, as recommended by the American Headache Society. The treatments are not given more often due to a small possibility that if you receive Botox more frequently, your body might build up antibodies to botulinum toxin. Those antibodies could in theory prevent Botox from working with future injections.

For many people, treatment with Botox alone is sufficient to control their chronic headaches. However, some people require more care, including additional medications to prevent migraine attacks. These may include cardiovascular drugs, such as beta blockers and calcium channel blockers; certain antidepressants; and some anti-seizure medications. Medications taken at the time of a migraine headache also can be useful.

The most common side effects of Botox injection include swelling or bruising at the injection site. Uncommonly, the medication may spread into nearby tissues and cause problems, such as a drooping eyelid, eyebrows that look out of place, dry eyes or excessive eye tearing. This tends to happen more in people who already have some eye drooping or are more sensitive to botulinum toxin. Sometimes, changing the injections to a slightly different location can reduce this side effect.

Although rare, it is possible that the effect of botulinum toxin may spread to other parts of the body and cause symptoms such as muscle weakness, vision problems, trouble speaking or swallowing, or difficulty breathing. Doctors generally recommend against using Botox if you are pregnant or breastfeeding because the medication's effects on a fetus are not known.

Botox injections are expensive. They can cost several thousand dollars per set of injections. Many insurance companies will cover the injections if a patient meets criteria for chronic migraine headache. For at least three months, a person must have a headache occurring on 15 or more days per month that has the features of a migraine on at least eight days per month. It is best to speak to a health care professional about options.

Before moving forward with Botox injections, make sure you are under the care of a licensed and skilled health care professional. Botox can be dangerous if it is given incorrectly, so it is important that these injections be administered by a physician, nurse or another specialist with experience using them for chronic headaches.

I recommend asking for a referral from your primary care provider or neurologist. A skilled and properly trained health care professional can discuss the procedure with you in detail and help you decide if it fits your needs. — Dr. Mark Whealy, Neurology, Mayo Clinic, Rochester, Minnesota

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