US Pharm. 2010;35(12):102 

In a large clinical study of nearly 2,500 gay men published by the New England Journal of Medicine, researchers found that the men taking Truvada were 44% less likely to become infected with the AIDS virus than an equal number taking placebo. The study, nicknamed iPrEx, was coordinated by the Gladstone Institutes of the University of California, San Francisco. When only the men whose blood tests showed that they had taken their pill faithfully every day were considered, however, the pill was more than 90% effective, said Anthony S. Fauci, MD, head of the infectious diseases division of the National Institutes of Health.

The protection method, known as pre-exposure prophylaxis, is the first new form available to men, especially those who cannot use condoms because they sell sex, are in danger of prison rape, are under pressure from partners, or lose their inhibitions when drunk or high. Truvada, a combination of tenofovir and emtricitabine that prevents the virus from replicating, is currently available by prescription in many countries.