Today, the U.S. Food and Drug Administration announced its approval of the first drug shown to reduce the chance of HIV infection in high-risk individuals: those who are uninfected and are sexually active with HIV-infected partners. The drug, called Truvada, is manufactured by San Francisco-area biotech Gilead Sciences and is taken as a daily oral pill. 

Left unchecked, HIV, the virus that causes AIDS, can destroy an infected person’s immune system and leave them vulnerable to life-threatening infections from other pathogens or cancer. Scientific progress in recent years has enabled HIV-infected patients to stave off the symptoms AIDS for years (see Technology Review’s Can AIDS be cured? from two years ago) but there is still no cure.

Truvada prevents HIV from reproducing inside human cells is already approved as a treatment for infected patients when combined with other anti-viral medications.

The prevention-capability of Truvada was tested in two clinical trials. In nearly 2,500 men with high-risk behavior, which included having unprotected sex with infected partners or with partners with unknown HIV-status, the anti-viral compound reduced the risk of an HIV infection by 42 percent if the drug was taken as directed. In another study with nearly 4,800 heterosexual couples in which one partner was infected and the other was not, Truvada reduced the risk of infection by 75 percent.

Gilead will collect viruses from any patient who acquires HIV while on Truvada in order to look for resistance to the compound.