CHICAGO (AP) - A drug used to fight nausea in cancer patients can help the most difficult-to-treat alcoholics significantly reduce their drinking, research suggests.

Success with the drug ondansetron comes amid a growing search for new medications to help treat a disease that affects some 14 million Americans.

In the past half-century, just two drugs have been approved to treat alcoholism, though studies on a number of others are under way.

Researchers from the University of Texas Health Science Center in San Antonio reported preliminary results with ondansetron in Wednesday's Journal of the American Medical Association.

Ondansetron worked in patients with early-onset alcoholism, who represent about 3.5 million of the nation's alcoholics, said Dr. Bankole Johnson, a psychiatrist who led the study.

These alcoholics, who develop problem drinking at or before age 25, are believed to have a biological predisposition toward alcoholism. They often respond poorly to counseling, exhibit anti-social behavior and have a high relapse rate.

An imbalance between two chemical messengers in the brain, serotonin and dopamine, is believed to create a craving for alcohol in early-onset alcoholics, Johnson said. Ondansetron's ability to regulate the serotonin-dopamine interaction may explain why it was effective only in such alcoholics, he said.

The study involved 271 alcoholics who were given ondansetron twice daily or a dummy pill for 11 weeks. Weekly behavioral therapy also was included.

Three different doses were tested, with the middle dose proving most effective. Alcoholics on that dose had an average of about 1.50 drinks daily compared with nearly 3.50 drinks daily for the placebo group. They also abstained from drinking for an average of about 70% of the study days, compared with 50% for the placebo group.

The findings could lead to better ways to treat alcoholism and to tailor treatment to specific types of alcoholics, Dr. Henry Kranzler of the University of Connecticut wrote in a JAMA editorial.

Glaxo Wellcome Inc. makes ondansetron. The National Institute on Alcohol Abuse and Alcoholism funded the study.

(US TODAY HEALTH)