When Truvada, an HIV-prevention medication, was first approved for preventative use by the FDA in 2012, it received a mixed response. Although the pill promised to decrease the incidence of HIV, critics worried that it would provide a false sense of security and promote riskier sexual behavior. Now, Kaiser Permanente has completed a two and a half year long study measuring the effects of Truvada on individuals in San Francisco, and found the pill to be 100 percent successful in preventing HIV.

Their results, published in the Journal of Infectious Diseases, observed 657 high-risk individuals who took the blue pill each day for over two years. During that time, not a single person contracted HIV.

Critics of the pill have argued that a medication like Truvada would lead to riskier behavior—and indeed, the participants in the recent study did use fewer condoms (more than 40 percent said their condom use had decreased) and 50 percent contracted sexually transmitted diseases other than HIV. While those infections are undesirable, they can be easily treated with antibiotics, while HIV cannot. Most of the participants said their number of sexual partners did not change.

In earlier clinical trials, Truvada effectively prevented HIV in 86 percent of participants, but the recent research is the first “real world” examination of the pill.