A daily HIV medication called Truvada may be effective at preventing HIV-negative gay men at a high risk for infection from contracting the virus, new evidence suggests. According to a report from Philly.com, the treatment, also know as pre-exposure prophylaxis (PrEP), was reported to be very effective at preventing new HIV cases in the September 9 issue of The Lancet.

Truvada, or tenofovir-emtricitabin, has been shown to prevent new cases of HIV in previous studies, but it remained unclear if the benefits of the drug would be outweighed by a perceived ability to engage in more risky behavior on the part of patients.

A new study led by Sheena McCormack from the Medical Research Council at University College London, led clinical trials at 13 sexual health clinics in England examining HIV-negative gay men who engaged in unprotected sex within the past 90 days.

The scientists assigned 275 of the men in the study to receive Truvada treatments immediately. An additional 269 men received the treatment after a one-year delay. The researchers followed up with the participants once every three months, and each participant was aware of their assigned treatment group.

In the group that received treatment right away, only three men contracted HIV, while 20 cases were reported in the delayed treatment group. The men in the immediate treatment group showed an 86 percent relative drop in the risk of infection when compared to the delayed treatment group.

“This finding is highly encouraging for PrEP implementation, although quantifying the likely demand in the U.K. remains challenging. The impressive reduction in HIV incidence in people taking PrEP, without a measurable increase in other sexually transmitted diseases, is reassuring for clinical, community, and public health stakeholders,” said McCormack.