In a series of votes, a Food and Drug Administration advisory panel recommended approval of the daily pill Truvada for healthy people who are at high risk of contracting HIV, including gay and bisexual men and heterosexual couples with one HIV-positive partner.
The FDA is not required to follow the panel's advice, though it usually does. A final decision is expected by June 15.
An estimated 1.2 million Americans have HIV, which attacks the immune system. Unless it's treated with antiviral drugs, it develops into AIDS, a fatal condition in which the body cannot fight off infections.
If Truvada is approved, it would be a breakthrough in the 30-year campaign against the AIDS epidemic. There have been no other drugs proven to prevent HIV and a vaccine is believed to be decades away.
Gilead Sciences Inc., which is based in Foster City, Calif., has marketed Truvada since 2004 as a treatment for people infected with HIV.
Researchers first reported that Truvada, which is a combination of two older HIV drugs Emtriva and Viread, could prevent people from contracting HIV in 2010. Results of a three-year study show that daily doses cut the risk of infection in healthy gay and bisexual men by 44 percent, when accompanied by condoms and counseling. Another study found that Truvada reduced infection by 75 percent in heterosexual couples in which one partner was infected with HIV and the other was not.
Because Truvada is already on the market to manage HIV, some doctors already prescribe it as a preventive measure. FDA approval would allow Gilead Sciences to formally market its drug for that use.
The Associated Press contributed to this report.