(Reuters) - Drugmaker Eli Lilly and Co said on Friday its acute migraine drug lasmiditan succeeded in a key late-stage study, setting the stage for U.S. regulatory approval.

About 40 million Americans suffer from migraine - intense headaches characterized by throbbing pain and sensitivity to light and nausea. The disorder, which can last for days, is incurable.

The size of the migraine market is expected to balloon to more than $10 billion in 2025 from $3 billion in 2015 in the United States and other developed countries, healthcare research firm Decision Resources Group said last year.

A clutch of drugmakers including Lilly are racing to grab a piece of this lucrative, under-served market.

Lilly’s trial tested three doses of lasmiditan against a placebo. Patients in the trial had an average of more than five migraine attacks per month.

At two hours following the first dose, a higher percentage of patients treated with lasmiditan were migraine pain-free compared to those on a placebo, meeting the study’s main goal.

Indianapolis-based Lilly originally discovered lasmiditan, but licensed out the oral drug to CoLucid Pharmaceuticals in 2005. Lilly bought CoLucid for $960 million earlier this year.

Lilly said it expected to file a U.S. marketing application for lasmiditan in the second half of 2018.

Currently, migraine patients are treated with triptans, a class of drugs that hit the market in the 1990s. Triptans work by constricting blood vessels in the brain and cannot be used in up to 35 percent of patients due to high cardiovascular risk.

A host of other drugs - including anti-depressants, medicines for hypertension and even botox - are also used to treat migraine, but with little success.

Lilly has another migraine drug in development called galcanezumab, which works differently from lasmiditan and targets a protein associated with pain signaling called CGRP.

Unlike lasmiditan, galcanezumab is being evaluated as a treatment to prevent migraines in patients who suffer from a severe form of the disorder.

Companies including Amgen Inc, Teva, Allergan, Biohaven and Alder Biopharmaceuticals also have CGRP drugs to prevent and treat migraine in the latter stages of development.

Amgen submitted a U.S. application to market its migraine drug, erenumab, in May.

Migraine costs the U.S. about $36 billion in healthcare and lost productivity, according to the Migraine Research Foundation.

Lilly’s shares, up about 11 percent this year, were little changed in early trading.