A medicine approved last month to treat AIDS also shows promise against hepatitis B.

The drug, 3TC, suppresses the hepatitis B virus in people with chronic infections, stopping its damage to the liver, researchers reported.

About 1 million Americans are thought to be infected with hepatitis B, which, left untreated, can lead to cirrhosis, liver failure and liver cancer in a small proportion of victims.

Currently, the only treatment for hepatitis B is interferon. This therapy can permanently eliminate the virus in about one-third of patients. It must be injected for four to six months and often has unpleasant side effects, including flu-like symptoms, fatigue and depression.

Unlike interferon, 3TC is given in pill form and carries few side effects.

The study is published in today’s issue of the New England Journal of Medicine. It was financed by Glaxo Wellcome Inc. of Research Triangle Park, N.C., which makes 3TC.