TUESDAY, April 24 (HealthDay News) -- Botox is considered a preventive medication for debilitating migraine headaches, but a new review finds that it may only help people with chronic migraines or chronic daily headaches. And, even then, the effect appears to only be "small to modest."

The review found that Botox (botulinum toxin A) was no help for people with episodic migraines (fewer than 15 a month) or chronic tension-type headaches.

"Our analyses suggest that botulinum toxin A may be associated with improvement in the frequency of chronic migraine and chronic daily headaches, but not with improvement in the frequency of episodic migraine, chronic tension-type headaches or episodic tension-type headaches. However, the association of botulinum toxin A with clinical benefit was small," wrote the authors of the review.

Still, the review's lead author, Dr. Jeffrey Jackson, said, "If I was having more than 15 migraines a month, I'd give Botox a try. It has few side effects. And, if it helps, you can go 90 days without as many headaches and without daily side effects." Jackson is a professor of medicine at the Medical College of Wisconsin in Milwaukee.

Results of the review are published in the April 25 issue of the Journal of the American Medical Association.

More than 40 percent of adults experience tension-type headaches at some point in their lives, according to background information in the article. Between 8 and 18 percent of adults have had migraines.

Treatment for these serious headaches fall into two general classes: abortive or preventive. The abortive medications are faster-acting, and can help stop a migraine or its symptoms while it's occurring. Preventive medications are taken to stop the headaches from occurring in the first place.

Botox's effect on migraines was discovered coincidentally when people who were having Botox injections to lessen lines and wrinkles in their foreheads noticed that their headaches were improved.

The current review examined 31 clinical trials. Twenty-seven were comparisons of Botox to placebo, including 5,313 patients. The remaining four studies were randomized clinical trials comparing Botox to medications commonly used to treat serious headaches. The drugs included amitriptyline (Elavil), prednisone, topiramate (Topamax) and valproate (Depakote).

When the researchers looked at the placebo-controlled trials, they found that Botox was associated with about two fewer headaches a month for people with chronic migraines and those with chronic daily headache. There was no statistically significant difference in people with episodic migraines or chronic tension-type headaches who were treated with Botox vs. placebo.

Botox wasn't associated with a reduction in the frequency of chronic migraines compared to topiramate or amitriptyline, or in the reduction of frequency of chronic or episodic migraines compared to valproate, according to the review. Botox did reduce headache severity more than methylprednisone, according to one study included in the review.

Side effects from Botox included a drooping eyelid, muscle weakness, neck pain, neck stiffness, skin tightness and a tingling, burning or numb sensation on the skin.

"If done properly, there really aren't substantial (side) effects from the use of Botox," explained Dr. Ezriel Kornel, a neurosurgeon at Northern Westchester Hospital in Mt. Kisco, N.Y. "But, over time the effect may wear off. Some people can develop an immunity to Botox."

Both Jackson and Kornel noted that there was a large placebo effect seen in many of the studies. "It's hard to know if most of the benefit was from the drug or from the placebo effect," said Jackson, who added, "but, patients don't care if it's a placebo effect."

Kornel said that the review showed that there is definitely some benefit from Botox for those with chronic migraine and chronic daily headache. "Chronic migraines are the hardest headaches to treat, and this gives us one more treatment in our armamentarium. It's a reasonable alternative to the use of long-term daily medications that can have side effects," Kornel said.

He said there are also other treatments that can help these types of headaches, and what's most important for someone who has debilitating headaches is to see a doctor who specializes in treating headaches. "A headache specialist has the whole array of treatments at their disposal," he said.

More information

Learn more about migraine headaches and their treatment from the National Headache Foundation.