BOSTON — An experimental new medicine offers quick, effective treatment of migraine headaches, shutting off the pain completely for most victims, a study shows.

The research shows that the drug, sumatriptan, offers relief for most sufferers within an hour or two of being injected. Doctors who tested the medicine called it “a highly effective, rapid-acting and well-tolerated treatment for migraine attacks.”

Their study, conducted on 639 people with severe headaches, is the latest of a series of recent reports demonstrating the effects of the medicine, which is produced by Glaxo Inc. Sumatriptan has not yet been approved by the U.S. Food and Drug Administration for routine use.

The study was conducted by Dr. Michel D. Ferrari of University Hospital in Leiden, Netherlands, along with doctors from Canada, Israel, South Africa and five European countries. It was published in the New England Journal of Medicine.

A second study in the journal, directed by Dr. K. Ekbom of Karolinska Institute in Stockholm, found the drug to be effective against cluster headaches, as well.

In both studies, doctors compared sumatriptan with placebos, rather than other migraine medicines. They said no effective, widely accepted treatment exists.

However, in an editorial reviewing the work, Dr. Neil H. Raskin of the University of California, San Francisco, disputed this conclusion. “Several effective treatments for both disorders are already available, despite assertions to the contrary in both papers,” he wrote.

He said sumatriptan is interesting because it is a so-called designer drug, a medicine created specifically to take advantage of a particular biological feature of a disease.

Sumatriptan apparently works by interfering with the body’s use of a messenger chemical in the brain known as serotonin. Although doctors have long known that serotonin plays some role in migraines, they still do not understand precisely how sumatriptan relieves the attacks.

The migraine study showed that after two hours, about 90 percent of those getting sumatriptan found their headaches were mild or had gone away completely, compared with one-third of those getting dummy shots.

Also in testing stages are a new version of the drug dihydoergotamine, or DHE, another injectable serotonin blocker that works in a fashion similar to sumatriptan. Sandoz Pharmaceuticals Corp., its maker, said the new version will be available in a nasal spray for easier administration.