Dr. Lisa Sterman holds up a Truvada pill at her office in San Francisco on May 10, 2012. The pill, already used to treat people with HIV, also helps prevent the virus from infecting healthy people. (Associated Press)

Photo by: Jeff Chiu

Dr. Lisa Sterman holds up a Truvada pill at her office in San Francisco on May 10, 2012. The pill, already used to treat people with HIV, also helps prevent the virus from infecting healthy people. (Associated Press)