The Food and Drug Administration approved on July 16 the first drug that has been shown in clinical trials to reduce the risk of HIV infection, an important step forward in the 30-year battle against HIV/AIDS.

Doctors will be able to prescribe Truvada, a pill made by Gilead Sciences, as a preventive measure to people who are at high risk of HIV infection, such as those with an HIV-positive partner.

The new drug could play an important role in reducing the number of new HIV cases, which has held steady for the past 15 years in the U.S. at 50,000 per year. An estimated 1.2 million Americans currently have HIV, with 240,000 unaware that they are infected.

Truvada has been approved since 2004 as a treatment for people with HIV infection, but two recent clinical trials showed that the drug may also reduce the risk of infection in HIV-negative people.

A three-year study showed that, when used alongside condoms and counseling, Truvada cut the risk of infection by 42 percent in healthy bisexual and gay men. A 2011 study found a reduced risk of 75 percent in heterosexual couples in which one partner was HIV-positive.

Some groups, however, such as the AIDS Healthcare Foundation, are concerned that the HIV prevention drug may encourage risky behavior by giving people a false sense of security. This may include not using condoms, the most effective way to reduce the risk of infection.

In response to these concerns, the FDA approved Truvada as part of a comprehensive HIV prevention strategy.

“We stress that PrEP [pre-exposure prophylaxis] with Truvada must include safer-sex practices, counseling, and HIV testing,” Debra Birnkrant, MD, the FDA’s director of antiviral products, said at a news conference. “Truvada should not be used alone for HIV prevention.”