Prescribing an antiretroviral (ARV) to HIV-negative injection drug users, a practice known as pre-exposure prophylaxis (PrEP), cuts in half their risk of acquiring the virus, The New York Times reports. Furthermore, those who did the best at adhering to the PrEP regimen saw a three-quarters reduction in risk. The Centers for Disease Control and Prevention (CDC) sponsored the research in Thailand that yielded these results, which complete an optimistic portrait of PrEP’s efficacy. Tenofovir, the active agent in PrEP, can now officially lower risk for all the main groups at risk of becoming infected with HIV: injection drug users, babies of HIV-positive mothers, gay and bisexual men as well as heterosexuals.

“This is a significant step forward for HIV prevention. We now know that PrEP can work for all populations at increased risk for HIV,” Jonathan Mermin, MD, director of CDC’s division of HIV/AIDS prevention, said in a release. “Injection drug use accounts for a substantial portion of the HIV epidemic around the world, and we are hopeful that PrEP can play a role in reducing the continued toll of HIV infection in this population.”

Called the Bangkok Tenofovir Study, the research was conducted by a partnership through the CDC, the Bangkok Metropolitan Administration and the Thailand Ministry of Public Health. They studied more then 2,400 adults at 17 Bangkok drug-treatment clinics. The participants were randomly assigned to take a daily dose of tenofovir or a placebo. Everyone in the study also received HIV prevention counseling, monthly HIV testing and a risk-reduction package addressing both sexual and drug-related risk factors.

A total of 17 participants among the 1,204 taking tenofovir became infected with HIV, while 33 participants of the 1,207 taking the placebo acquired the virus, meaning that PrEP yielded a 49 percent reduction in risk of infection for the group.

Some of those in the study chose to be monitored taking their therapy. The researchers conducted a separate analysis of those members of this group who took tenofovir at least 71 percent of the days and who did not miss more than two days in a row. They found that these more-adherent participants had a 74 percent reduction of risk.

“These findings add to the mounting scientific evidence that high adherence to PrEP is essential to achieve the greatest benefit,” Mermin said. “When used consistently and in conjunction with other proven prevention measures, PrEP can provide important additional protection for many people who remain at high risk for HIV, including those who inject drugs.”

To read the New York Times story, click here.

To read the CDC’s press release on the study, click here.