Gilead Sciences has filed an application with the Food and Drug Administration (FDA) to approve its combination drug Truvada (emtricitabine and tenofovir) as pre-exposure prophylaxis (PrEP) therapy for men who have sex with men (MSM) and heterosexual men and women at risk of becoming infected with HIV. Truvada is to be taken once a day, every day, regardless of whether you’re sexually active that day. The application for approval uses data from the Iniciativa Profilaxis Pre Exposicion, or iPrEx, study—a clinical trial that examined the effects of PrEP on HIV transmission among MSM. According to the study's results, Truvada PrEP resulted in 44 percent fewer infections among MSM who used the drug, compared with those who used a placebo. Among participants who were more adherent, the rate of protection was more than 90 percent. (Participants also received condoms and HIV prevention support; the benefits of PrEP were in addition to these HIV prevention benefits.) An equivalent study among close to 5,000 serodiscordant heterosexual couples in Uganda and Kenya showed similar results, and an Open Label Extension of the iPrEx study is underway to provide long-term information on PrEP’s long-term health effects.