In a study of 403 self-reported heavy drinkers, participants were told to take a pill whenever they felt the urge to over-indulge in alcohol. There weren't told whether the pill was nalmefene -- sold as Revex -- or a placebo.

Both groups of patients were able to reduce the numbers of heavy-drinking days, but those taking the active drug had fewer days during which they drank heavily.

"It has a robust and sustained effect in reducing harmful heavy drinking in a large study population," said Sakari Karhuvaara, a medical researcher in Turku, Finland. Karhuvaara is a former employee of Biotie Therapies Corp., the manufacturer of nalmefene.

The drug maker supported the new study. Its results appear in the July issue of Alcoholism: Clinical & Experimental Research.

Before the study, patients assigned to nalmefene treatment reported 15.5 average heavy-drinking days each month. During the first three months of treatment, the average number of heavy-drinking days was about eight to nine.

The drinkers assigned to the placebo group had somewhat less dramatic reductions. They averaged 16.2 heavy-drinking days a month before the study and about 10 to 12 days during the trial.

Researchers double-checked participant-reported alcohol consumption changes with tests that measured alcohol-use biomarkers in the blood.