Details from two studies examining Allergan Inc.'s (AGN) wrinkle fighter Botox as a chronic migraine headache treatment could help secure broader access to a market potentially valued at $500 million a year for the company.

Allergan announced key results from the company-sponsored studies a year ago, including the fact that one missed its main goal but succeeded on another point the company said the Food and Drug Administration cares about most: reducing the frequency of days with headaches. Data from the studies made public Thursday showed good performance on this front, according to analysts.

The data "are solid and should lead to FDA approval" of Botox as a treatment for people with frequent migraines, according to William Blair's Ben Andrew.

Allergan shares, which received a big boost when the trial results were released last September, slipped 14 cents to $56.04 early Thursday. Jefferies analyst Peter Bye noted that investor expectations for solid data were already "firmly in hand."

This is an important growth opportunity for the injectable neurotoxin, which is perhaps best known for treating facial creases and posted $1.31 billion in sales last year. Allergan has estimated the migraine market could eventually be worth up to $500 million a year in additional sales, should the FDA grant approval, and some analysts supported that assessment after seeing the study details.

There is already an estimated $50 million market for Botox as a migraine treatment, since doctors can use approved drugs for other purposes. But Allergan - which received a Department of Justice subpoena related to Botox sales and marketing early last year - can't market Botox for headaches without FDA approval.

Approval could also help pave the way for broader insurance reimbursement. Additionally, Wells Fargo analyst Larry Biegelsen said potential endorsement from the American Academy of Neurology could drive off-label use if the FDA doesn't approve Botox for migraines next year.

Allergan didn't issue any statement in conjunction with the fresh study details, but spokeswoman Caroline Van Hove confirmed the company plans to file with the FDA by the end of the third quarter seeking clearance to market Botox for migraines. Analyst Bye sees potential for approval in early 2011.

The new data were made available by the American Headache Society and its international counterpart, which are hosting a meeting in Philadelphia this week. Thus far "abstract" details are available, which give a view into key numbers but not broad details.

Biegelsen said safety data need to be examined more closely. But he also said the data look positive and match up favorably compared with data for a well-known migraine drug - Johnson & Johnson's (JNJ) Topamax.

As a migraine treatment, Botox is aimed at people who suffer with the debilitating headaches at least 15 days a month and may not get relief from other treatments. The drug doesn't stop headaches altogether, but if it keeps them from occurring as often, it may be a useful tool.

The two trials included a total of 1,384 patients who received either Botox or a fake treatment and were tracked for 24 weeks. In the first trial, Botox reduced the number of headache days by 7.8 days, compared with a 6.4-day reduction among patients on a placebo.

In the second trial, Botox-treated patients saw a nine-day reduction in migraines, compared with a 6.7-day reduction among placebo-treated patients. The gap between the results with Botox and placebo is considered statistically significant.

The first trial's main goal was to lessen the number of migraine episodes compared with a placebo, and the trial failed on that measure. But it succeeded on the secondary goal of cutting headache days, which Allergan has said the FDA is most interested in seeing anyway.

Due to this result, Allergan switched the second study's goals before data were unmasked, and that study was successful on both headache days and episodes.

-By Jon Kamp, Dow Jones Newswires; 617-654-6728; jon.kamp@dowjones.com