On online dating sites, Matthew Sachs identifies himself as a 5-foot-8, 130-pound grad student who likes hiking, performance art and community service. He says he’s interested in meeting a broad range of guys, from jocks to geeks, and notes that — oh, by the way — he’s “On PrEP.” Those four letters stand for a daily medical regimen in which healthy individuals take a blue oval pill to lower their risk of becoming infected with HIV. The treatment, known as pre-exposure prophylaxis, has become so common in the Bay Area’s gay community that it’s frequently mentioned in social media profiles from Facebook to Scruff.

Since the first breakthrough research was published in the New England Journal of Medicine in 2010, the once-a-day dose of Truvada has consistently been shown to reduce the risk of HIV infection by as much as 90 percent. The results of the most recent study, which was published in September, were, even more, encouraging: Not one of the 600 people taking the drug became infected over two years. FULL REPORT