The single most important thing you can do after unprotected sex to prevent HIV is start a medication called PEP (post-exposure prophylaxis) within 72 hours. Every hour matters: the sooner you begin, the better it works. PEP reduces the risk of HIV infection by more than 80%, and that number is likely significantly higher when you take every dose as prescribed for the full 28-day course.
Get PEP as Fast as Possible
PEP is a 28-day course of antiretroviral drugs that stops HIV from establishing itself in your body after an exposure. The virus needs time to replicate and spread, and PEP interrupts that process. But the window is tight: you must start within 72 hours (3 days) of the exposure, and earlier is always better. If it’s been less than 24 hours, treat it like an emergency and go now.
You can get PEP from your regular doctor, an urgent care clinic, or an emergency room. When you arrive, tell them directly that you may have been exposed to HIV and need PEP. Don’t wait for a scheduled appointment if that means losing hours. Emergency rooms can prescribe PEP at any time of day or night, including weekends.
If more than 72 hours have passed, PEP is no longer considered effective. At that point, the focus shifts to testing and, if needed, early treatment. But if you’re anywhere inside that 72-hour window, even close to the edge, it’s still worth going in.
What PEP Involves
PEP is a combination of antiretroviral medications taken once or twice daily for exactly 28 days. Your provider will choose a regimen designed to minimize side effects and keep the pill count low, which makes it easier to finish the full course. Completing all 28 days is critical. Stopping early or skipping doses dramatically reduces the protection PEP offers.
The most common side effects are nausea, vomiting, diarrhea, and fatigue. These are typically manageable and tend to ease after the first week or so. If side effects are making it hard to stay on track, contact your provider. They can sometimes adjust the regimen or suggest ways to manage symptoms so you don’t miss doses.
Where to Go and How to Pay
Cost is a real concern, but it shouldn’t stop you from seeking PEP. If you have insurance, your plan will generally cover the medication, though you may face a copay or deductible. If that’s a barrier, pharmaceutical companies that manufacture PEP drugs offer co-payment assistance programs that can reduce or eliminate your out-of-pocket costs. These programs typically cap your annual expense somewhere between $1,200 and $7,500 depending on the specific medication.
If you don’t have insurance, patient assistance programs can cover the medication entirely at no cost. Eligibility varies by manufacturer, but most programs cover individuals earning up to 300% to 500% of the federal poverty level. Your provider or the prescribing facility can help you apply. Keep in mind that these programs usually cover the medication itself but not the clinic visit or lab work, so ask about separate financial assistance for those costs.
The Testing Schedule After PEP
Starting PEP isn’t the end of the process. You’ll need HIV testing at three points: at the time you start PEP (baseline), at 4 weeks after the exposure, and again at 12 weeks. The 12-week test is the one that reliably confirms whether HIV infection occurred. A negative result at that point means you can reasonably rule out infection from this particular exposure. Testing at six months is no longer recommended as standard practice.
These follow-up appointments also give your provider a chance to check how you’re tolerating the medication and address any issues with side effects or adherence. Some clinics handle follow-up by phone rather than in-person visits.
Get Tested for Other STIs Too
Unprotected sex carries risk for more than HIV. At the same visit where you start PEP, ask about screening for chlamydia, gonorrhea, syphilis, and other common infections. Many of these can be detected through simple urine tests or swabs (rectal, throat, or genital depending on the type of contact). Some STIs don’t produce symptoms for weeks, so testing is important even if you feel fine.
If You’re at Ongoing Risk, Consider PrEP
PEP is designed for emergencies, a one-time exposure you didn’t plan for. If unprotected sex is something that happens in your life more than occasionally, PrEP (pre-exposure prophylaxis) is the long-term counterpart. PrEP is a daily or on-demand medication taken before potential exposure, and it reduces the risk of getting HIV from sex by about 99% when taken consistently. Your provider can discuss switching from PEP to PrEP once your 28-day course and follow-up testing are complete.
The transition is straightforward: after finishing PEP and confirming a negative HIV test, you can begin PrEP without a gap. Many of the same financial assistance programs that help cover PEP also apply to PrEP, and additional federal programs exist specifically for PrEP coverage.