An American study looking at the real-world use of pre-exposure prophylaxis (PrEP), found that men who have sex with men (MSM) and transgender women adhered at high rates to daily Truvada (tenofovir/emtricitabine), especially if they were at higher risk of contracting the virus. There was no evidence of greater sexual risk-taking during the study.

Between October 2012 and January 2014, the U.S. PrEP Demonstration Project enrolled 557 participants at clinics in San Francisco, Miami and Washington, DC.

Sixty-three percent of the 294 tested participants had drug levels at all study visits suggesting they were taking Truvada at least four days a week, which researchers have found offers maximum protection against HIV. Three percent of the participants had drug levels at all study visits suggesting they were taking fewer than two pills each week, while 34 percent of participants had inconsistent adherence patterns across visits.

Having stable housing and reporting a higher number of condomless anal sex partners were each linked with a greater likelihood of taking four or more pills per week.

Two people contracted HIV during the study. Both had low or undetectable PrEP levels.

“This study provides further evidence that many men are eager to take PrEP, and, with relatively streamlined counseling and support, adherence levels are high,” says the study’s co-investigator, Susan Buchbinder, MD, an assistant clinical professor at the University of California, San Francisco.

“However,” she adds, “we need specific outreach efforts to African-American MSM and transgender women, as these populations were underrepresented in our study.”