Women who suffer the misery of migraines at the time of their period could be helped by a new treatment, according to a study.
Migraine: The most common neurological condition in the West
The disabling headaches can be prevented by taking a new drug before menstruation, a US trial suggests.
Around four million women in the UK alone suffer from migraines, many triggered by hormonal changes at the 'time of the month'.
The therapy, frovatriptan succinate, is already available in the US and is about to be licensed in the UK.
Frovatriptan is a member of a class of drugs called triptans, which reduce inflammation of certain blood vessels in the brain thought to cause pain.
It is currently prescribed for acute migraine attacks but its use could be extended as a prevention for menstrually associated migraines (MAM).
The US trial involved 545 women with MAM who were treated for three months with frovatriptan or placebo.
They were given tablets for six days - two days before and four days during their period.
About half of patients on the drug had no headaches while taking it compared with about a quarter of the placebo group.
"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 the principal investigator of the study, Prof Stephen Silberstein of Jefferson Medical College of Thomas Jefferson University.
"While MAM is not a widely recognised term, millions of women have been suffering for many days each month.
"When the women we studied took frovatriptan for six days, many of them did not have their expected disabling migraine headaches."
Ann Turner of the Migraine Action Association in the UK said a lot of women were more susceptible to migraine around the time of their period.
"Studies have suggested that this drug can be useful for women to take every day as a preventative treatment," she said.
The data will be presented at the American Academy of Neurology Meeting in Honolulu.