The Basics

PrEP works if you take it.

Across populations, geography and route of exposure the data all point in the same direction—daily TDF-based oral PrEP works if you take it.

It's safe.

There were no major adverse events observed in any of the trials. Some mild side effects were reported, the majority of which went away over time.

Adherence is essential.

Each of the trials that found a benefit from taking PrEP also found that people who had high levels of adherence had high levels of protection. Lower adherence was associated with low or no protection.

It works for both cisgender and transgender men and women.

PrEP is highly protective in both cisgender and transgender men and women. It takes longer to establish protection in vaginal tissue than in colorectal tissue, and both cisgender and transgender women need to be adherent to daily regimens. But when people take it as prescribed, they are protected.

People who can benefit most from PrEP can — and do — take it, but program design matters, a lot.

Early implementation projects showed that individuals with high HIV risk could also be highly adherent to PrEP. As PrEP moves into large-scale, national programs, it is clear that initiation and use require providers, peers, communities and potential users to engage with programs centered on the needs of those who use PrEP.

Resistance is rare.

Individual cases of HIV drug resistance have been observed in trials to date. Resistance can develop if a person acquired HIV while on PrEP and went on taking PrEP (which is only one or two antiretrovirals) during the time before diagnosis. The documented cases of resistance appear to have occurred in participants who were already HIV-positive when they began taking PrEP, but still in the “window period” of early infection when detection is more difficult. These individuals tested HIV-negative on the trials’ screening tests. This reinforces the importance of regular testing for anyone initiating or taking PrEP. There are few cases of individuals who took TDF/FTC as PrEP, were exposed to virus resistant to both TDF and FTC, and became infected while taking PrEP. Transmission of multi-drug resistant strains is rare so widespread PrEP failure due to drug-resistant virus is highly unlikely.

Daily oral PrEP doesn’t protect against other STIs.

PrEP is a terrific HIV prevention tool. It doesn’t reduce risk of chlamydia, gonorrhea, syphilis or herpes. Male and female condoms do. Comprehensive access to PrEP, condoms, communication and counseling makes prevention work for all.

Someday soon, daily oral TDF-based PrEP may not be the only PrEP there is.

Other ARV-based primary prevention strategies are in the pipeline. In two or three years, PrEP may mean many different things!