PrEP has been available as an FDA-approved HIV prevention method since July 2012, making it roughly 13 years old as a prescription option. But the science behind it stretches back decades, and the drug itself existed years before anyone used it specifically for prevention.
The Science Started in the 1990s
The key ingredient in the first PrEP pill, a compound called tenofovir, showed promise against HIV in lab settings early in the 1990s. The real breakthrough came on November 17, 1995, when researchers published a landmark study in Science showing that tenofovir provided complete protection against a close relative of HIV in monkeys. All five monkeys given the drug before or shortly after exposure were fully protected, while none of the ten untreated monkeys were. That result, strikingly clean for an animal study, launched years of further research into whether the same approach could work in people.
Tenofovir was eventually combined with a second antiviral drug (emtricitabine) and sold as Truvada, which the FDA first approved on August 2, 2004, but only for treating people who already had HIV. The idea of giving it to HIV-negative people as prevention was still being tested.
The Trial That Changed Everything
The pivotal moment for PrEP came in November 2010, when the New England Journal of Medicine published results from a large international trial called iPrEx. The study enrolled gay and bisexual men and transgender women who were HIV-negative and found that taking a daily Truvada pill reduced their risk of getting HIV by about 44%. Among participants who took the pill most consistently, protection jumped to 73%.
Those numbers were significant enough for the FDA to act. In July 2012, the agency approved Truvada specifically for pre-exposure prophylaxis, making it the first drug ever approved to prevent HIV in people who don’t have it. That approval is the real starting point for PrEP as we know it today.
How PrEP Has Evolved Since 2012
PrEP hasn’t stayed frozen in its original form. Several major milestones have expanded how people can access it:
- 2015: The World Health Organization recommended PrEP for all people at substantial risk of HIV globally, not just in the U.S., helping drive adoption in dozens of countries.
- 2019 (June): The U.S. Preventive Services Task Force gave PrEP a Grade A recommendation, which triggered a requirement under the Affordable Care Act for most insurance plans to cover it with no out-of-pocket cost starting in mid-2020.
- 2019 (October): The FDA approved a second daily pill called Descovy for PrEP. It uses a newer formulation of tenofovir that may cause fewer kidney and bone side effects. One important limitation: it was only studied in men and transgender women who have sex with men, so it’s not approved for people whose primary risk comes from receptive vaginal sex.
- 2021 (December): The FDA approved Apretude, the first injectable form of PrEP. Instead of a daily pill, it’s given as a shot every two months (after two initial monthly doses). This was a major shift for people who found it hard to take a pill every day.
How PrEP Works in Your Body
PrEP works by placing antiviral drugs in your tissues before HIV ever shows up. If the virus enters your body through sex or shared needles, it needs to hijack your cells and copy itself to establish an infection. The drugs in PrEP block a specific enzyme HIV relies on to make copies of its genetic material. Without that step, the virus can’t take hold.
This protection isn’t instant. For receptive anal sex, daily PrEP pills reach their maximum effectiveness after about 7 days. For receptive vaginal sex or injection drug use, it takes closer to 21 days. The injectable version follows its own timeline based on the injection schedule.
How Effective PrEP Is Today
When taken consistently, PrEP is highly effective. Real-world effectiveness depends heavily on adherence, which is one reason the injectable option was developed. People who struggle with daily pills can maintain protection through bimonthly shots instead. The CDC describes PrEP as greatly reducing the chance of getting HIV from both sex and injection drug use, and multiple large studies have confirmed that near-perfect adherence brings the risk of HIV transmission close to zero.
From a 1995 monkey study to a daily pill in 2012 to bimonthly injections in 2021, PrEP has been a medical option for over a decade, with roots in research going back nearly 30 years.