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A new study backed by the National Institute of Health has discovered that certain populations at risk of HIV infection are actually very good at taking PrEP, the drug that can prevent infection.

Each of the three groups of people studied represented populations who have historically suffered from disproportionate HIV infection rates for a number of different reasons: In South Africa, the study focused on heterosexual women who have sex with men and in New York and Thailand the study zeroed in on men who have sex with other men and transgender women.

For 24 weeks, each of the participants were prescribed Truvada, a form of PrEP, and given detailed instructions on how the drug is meant to be taken. Participants were also given a choice as to how they took the drug: They could take the drug once daily, twice weekly (with the caveat that they also take incidental dosages immediately after sex,) or they could opt to only take the pill immediately before and after sex as they deemed necessary.

The researchers behind the study monitored how strictly participants in the study adhered to their Truvada regimens with a number of different data-tracking methods, such as routine bloodwork, self-reporting, and using specialized pill containers that tracked every instance of the prescription bottle opening.

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None of the participants was given a placebo in place of Truvada.

“During in-depth interviews at the Cape Town study site, the women reported that daily dosing was the easiest regimen to follow, as taking a pill each day established a simple-to-follow habit at a convenient time,” the NIH explained in a press release. “Focus groups of enrolled participants also indicated that community support and reminders delivered via cell phones aided adherence.”

Participants in other countries reported similar feelings: Sixty-five percent of the men from Harlem and 85 percent of participants in Thailand were able to adhere to daily dosages that would effectively protect them from HIV. Across the board, the people who chose to take the pill twice a week or immediately before and after sex were all observed as not taking the drug as often, and as a result some people ultimately contracted the virus.

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While it is unfortunate that some of the participants became HIV positive by the end of the trial, it’s important to understand that the importance of the study’s information about the people who stuck with their regimens.

One of the most common arguments against the widespread use of Pre-Exposure Prophylaxis as a tool to prevent HIV infection is that the people who need the drug the most aren’t likely to take it properly. Similar to birth control, PrEP’s efficacy is directly linked to the regularity with which a person takes the drug.

In clinical trials, Truvada, the only FDA-approved form of PrEP currently on the market, reduced HIV infection rates by as much as 99 percent when people took the drug daily on a rigorous schedule. On the flip side of things, the drug’s effectiveness plummets when people skip dosages, leading many to claim that PrEP could ultimately cause more harm than good if people mistakenly assumed that they were having safe sex.

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With this new information, though, the push to get the people who could benefit to be on PrEP can move forward.

“This is an important step forward for optimizing HIV prevention strategies for people who would otherwise be at high risk for acquiring HIV infection,” said study chairRobert M. Grant, M.D., M.P.H. “The findings will inform the next generation of PrEP research and the development of best practices regarding PrEP adherence and counseling.”

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