SILVER SPRING, Md. — A drug already used to treat H.I.V. infection should also be approved to prevent it, an advisory panel to the Food and Drug Administration said on Thursday. The recommendation is the first time that government advisers have advocated giving antiviral medicine to healthy people who might be exposed through sexual activity to the virus that causes AIDS.

One panelist called approving the drug “an amazing opportunity to turn the tide on this epidemic.”

Studies have shown that people who take the medicine, Truvada, every day have a greatly reduced risk of infection.

The F.D.A. usually accepts the advice of its advisory panels, which are made up of outside medical experts.

On Thursday, after evaluating studies of the once-a-day pill and hearing scientific presentations, the panel recommended that Truvada be prescribed for people at high risk of infection, like gay men who have multiple sex partners, especially those who do not always use condoms, and people in relationships with someone who is H.I.V.-positive. Young black men who have sex with other men are at highest risk. The drug would also be recommended for other high-risk people, like prostitutes.