The answer doesn’t change based on how you feel, what the exposure was, or how worried you are by day 10. PEP is a 28-day course. One tablet, once daily, for 28 consecutive days. That’s it. The only variable is how well you stick to it, and that matters more than most people realise.

The duration is based on HIV’s biology, not a round number.

After HIV enters the body, it doesn’t spread instantly. It tries repeatedly to copy itself and integrate into your immune cells over a period of weeks. PEP works by maintaining drug levels in your system continuously high enough to block each of those attempts, the early ones, the ones that happen a week later, and the ones that might come even in the final days of the window.

28 days is the clinically established duration needed to suppress the virus through its full biological replication cycle after a single exposure. Stopping at day 14 or day 20 because you feel fine cuts that suppression short at the point when the virus still has opportunities to establish itself.

Partial courses mean partial protection. That gap is where HIV wins.

Think of it this way. If you stop PEP on day 21, you’ve given the medication seven fewer days to complete its job. The virus that was being continuously suppressed now has an uncontested window. If any HIV particles were still trying to replicate during those final days, they can now do so without resistance. Stopping early is one of the most common reasons PEP fails in cases where it otherwise should have worked.

This applies even if you started fast, even if your exposure was lower-risk, and even if you’ve had no side effects. None of those factors shorten the required course length. Complete all 28 days.

28 days is achievable with a simple system.

Set one alarm, keep it consistent. Take your PEP at the same time every day. Whether that’s with your morning coffee, at lunch, or before bed, pick a time and stick to it. Consistency is what protects you, not just the medication itself.

Keep it visible. Don’t leave it in a bag or drawer you rarely open. Keep it where you’ll see it. A pill organiser helps a lot of people track where they are in the course.

Take with food if nausea is a problem. The most common side effect of PEP is nausea in the first one to two weeks. Taking the tablet after a meal rather than on an empty stomach reduces this for most people significantly.

Contact our team if you’re struggling. If side effects are making adherence difficult, there are options. Don’t quietly stop the medication, message us. See our missed dose guidance if you’ve already missed a dose.

Finishing the course is the start, not the end.

PEP finishing doesn’t confirm it worked. The only way to confirm the outcome is HIV testing. Get a 4th generation HIV test at 45 days after the original exposure and a confirmatory test at 90 days. A negative result at 90 days is the definitive answer.

If your HIV risk is ongoing, that conversation should start before the PEP course ends, not after. PrEP can be started directly at the end of PEP with no gap in protection. Read our guide on what to do after finishing PEP.

Common questions about PEP duration.