Many people suffer from migraine headaches, but more than 5 million American women can count on them monthly -- right around the time of their periods.

"I literally dreaded getting my period because of the migraines I got every month," said Wanda Bernier, a Philadelphia mother of two. "For almost 20 years, I had to plan my life around having a five-day migraine each and every month and taking drugs constantly to get rid of the pain."

But neurologists at Thomas Jefferson University Hospital in Philadelphia may have found a long-acting therapy that could stop these monthly migraines before they start.

The drug, frovatriptan succinate, was tested in a nationwide study that found it prevented menstrually associated migraines in as many as half the women studied. Frovatriptan is in a class of drugs called triptans, which reduce inflammation of certain blood vessels in the brain thought to cause pain.

"We're excited about this study because this is the first time we've seen a triptan actually prevent these headaches in such a large number of women before they experience pain," said lead researcher Dr. Stephen Silberstein, professor of neurology at Jefferson Medical College.

Silberstein presented the findings Tuesday at a meeting of the American Academy of Neurology in Honolulu.

In the United States, about 9 million women suffer from migraines and about 60 percent of them, or 5.4 million, report an increased number of headaches associated with their menstrual periods, according to the study.

For the women in the study, migraines typically began between two days before and one day after the start of menstruation. The migraines lasted an average of 29 hours, and more than three-fourths of the patients reported moderate or severe headache pain.

"Menstrually associated migraines can last for days. Hormonal changes trigger these headaches, which are often long in duration and especially difficult to treat," Silberstein said. "Frovatriptan remains in the blood longer, so it is particularly well-suited to treat (these migraines)."

In the study, 545 women were treated for three months. They were given a placebo, a once-daily or twice-daily dose of frovatriptan two days before and four days during their menstrual periods.

The study, which was based at Jefferson, was conducted at 36 centers nationwide.

Researchers found that 50 percent of patients treated in the six-day period with 2.5 milligrams of frovatriptan twice daily had no headache. In addition, 39 percent of patients taking 2.5 milligrams of frovatriptan once daily had no headache, compared to 26 percent taking a placebo. Depending on the dose they received, frovatriptan significantly reduced migraine severity and duration.

The side effects patients reported from frovatripta included nausea, dizziness, headache and fatigue.

In an earlier study, Silberstein found that frovatriptan also was found to help prevent cluster headaches. According to researchers, cluster headaches are less common than migraines and extremely hard to treat. Sufferers sometimes describe attacks as a stabbing pain around the eye.