How effective is PEP?

When used correctly, PEP (post-exposure prophylaxis) is a highly effective emergency intervention to prevent HIV infection. Its success depends on two rules: act fast and take the full treatment.

Rule #1: Act as quickly as possible

This is the most important factor. PEP must be started as soon as possible after the exposure, ideally within the first few hours, and no later than 72 hours after. Beyond that window, it is no longer recommended. The sooner treatment begins, the better its chances of stopping the virus before it takes hold.

Rule #2: Take the full treatment

PEP is not a single dose. It is a course of antiretroviral medication taken every day for 28 days. Stopping early or missing doses reduces protection.

What does recent evidence show?

The "over 80%" figure you may have come across comes from a 1990s study of health care workers using a single medication (AZT). It does not reflect current treatments.

Today's PEP combines several modern antiretrovirals that are more potent and better tolerated. Comparing PEP to a placebo would be unethical, so there is no exact percentage for these treatments. Recent evidence is nonetheless very reassuring. In studies published in recent years on the combinations preferred today, no HIV infections were observed.

The rare infections reported with PEP are mostly explained by a new exposure after the treatment ended, and sometimes by a late start or by stopping before the full 28 days. That is why the two rules above matter.

After PEP

HIV testing is needed at the start of treatment and in the months that follow to confirm that PEP worked. This follow-up is provided by a physician. Our team can help direct you to available resources.

If you find yourself needing PEP more than once, PrEP may offer better day-to-day protection. It is taken before exposure rather than after. Learn more about toutPrEP

Think you were exposed to HIV in the last 72 hours? Visit our PEP page

This information is provided for informational purposes only, is not exhaustive, and may change. It does not replace an individual assessment by a health care professional.