HIV prophylaxis does not encourage risky behavior, study finds.

Despite concerns that a pill that prevents HIV infection would increase risks of contracting other sexually transmitted diseases through risky behavior, a new study found the risks remained stable.

New research shines a positive light on the once-a-day pill that prevents HIV infection. Research presented at the 2014 International AIDS Conference in Melbourne, Australia shows that pre-exposure prophylaxis may not encourage risky sexual behaviors that increase the risk of other sexually transmitted diseases. The study also indicates that strict adherence to one pill per day may not be as crucial as earlier research suggested.

“We’re encouraged,” said study leader Dr. Robert Grant, an AIDS expert at the Gladstone Institutes, a foundation affiliated with the University of California, San Francisco. “There’s a demand, there’s some forgiveness for missed doses. And it’s safe.”

The researchers studied 1,600 gay men and transgender women who were subjects of an earlier study that found that daily use of the drug Truvada lowered the risk of contracting HIV. These subjects were offered the drug for free after the first study period ended; about 75 percent elected to take the drug.

None of the subjects who took the drug at least four of seven days per week became infected with HIV. Among those who took the pills only two or three days per week, HIV infection risk was still lower compared with subjects who did not take the pills at all.

The researchers also found that the subjects who took Truvada did not engage in behaviors that increased their risks for contracting other infections. Nor did they observe any increase in the incidences of these other sexually transmitted diseases.

Truvada, which is produced and marketed by California-based Gilead Sciences, Inc., wholesales for $800 per month per individual in the U.S. where Gilead still holds exclusive rights. Overseas, generic forms sell for as little as $0.31 per day.

Earlier this year, the U.S. Centers for Disease Control and Prevention began recommending Truvada amidst concerns that the drug might encourage changes in behaviors that increased the risk of contracting other sexually transmitted diseases.

This study was funded by the U.S. National Institutes of Health. The report is published this week in the British journal The Lancet Infectious Diseases.