Injections of Botox, the wrinkle-fighting drug marketed by Allergan Inc. (AGN), were associated with small to modest benefits for chronic migraine sufferers but not for those affected by episodic migraine, according to a study published online in a medical journal Tuesday.

Chronic migraine sufferers are defined as people who suffer from headaches on 15 or more days per month. Episodic sufferers are those who suffer from headaches for fewer than 15 days.

The study, published on the website of the Journal of the American Medical Association Wednesday, was an analysis of previous randomized controlled trials comparing botulinum toxin, or Botox, with a placebo or other treatments for headaches among adults. Botox was associated with a reduction in the number of headaches per month from 19.5 to 17.2 per month for chronic migraine.

"There is clearly evidence of benefit for people who are suffering from chronic migraine," said principal investigator Jeffrey L. Jackson, who is also a professor of medicine at the Medical College of Wisconsin. He doesn't receive funding from Allergan.

"The benefit is on average pretty small," he said. He also noted that "the potential for a placebo effect is huge." The analysis found strong association of placebo with improvement in headaches over time.

Mitchell Brin, Allergan's chief scientific officer for Botox, said the findings are "very supportive of our label." But he said the analysis doesn't take into account other variables, such as cumulative hours of headache.

The U.S. Food and Drug Administration approved Botox as a treatment for preventing chronic migraine headaches in 2010, but so far literature on its effectiveness has been mixed.

The indication is an important one for Allergan. The company said on its fourth-quarter earnings call that the U.S. launch of Botox for migraine is progressing "better than planned." Wells Fargo said in a note earlier this month that based on recent market share data, it expects U.S. sales of more than $260 million in 2012.

Allergan shares closed Tuesday at $94.18, up 38 cents on the day and nearly 21% over the past 12 months.

-By Anjali Athavaley, Dow Jones Newswires; 212-416-4912; anjali.athavaley@dowjones.com

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