WASHINGTON — Botox, the botulism-based drug that has wiped wrinkles from the faces of millions, may get another approved use: stopping headaches.

Drugmaker Allergan said yesterday it has new evidence that its injectable drug can help relieve migraine headaches. Based on preliminary results from two company-funded studies, Allergan said it will ask the Food and Drug Administration to approve Botox for chronic migraine next year.

The FDA approved Botox to smooth wrinkles and age lines in 2002, and it has grown into a blockbuster product for Allergan, with $2.1 billion in sales last year. Doctors inject the drug directly into patients’ foreheads every four months, paralyzing facial muscles that create wrinkles.

Although Botox is not approved by the FDA for treating migraines, doctors have been using it in that way off-label.

Allergan compared results for migraine patients who received either Botox or a dummy injection every 12 weeks. In the company’s first study there was no difference in the number of overall headaches reported by patients taking Botox versus the dummy injection. However, Allergan said there was a significantly lower number of “headache days” reported by Botox patients. According to the company, FDA considers migraine days a more accurate treatment measure.

A second company study showed lower rates of migraines and migraine days for patients in the Botox group, according to Allergan.

Shares of Irvine, Calif.-based Allergan leapt on the news, rising $5.95, or 10.9%, to close at $60.53.