PEP (post-exposure prophylaxis) is an emergency course of HIV medications you take after a potential exposure to the virus. It must be started within 72 hours of exposure, and every hour counts. When taken correctly, PEP is estimated to be over 90% effective at preventing HIV infection.
The basic idea: HIV doesn’t establish itself in the body instantly. There’s a narrow window after the virus enters your system but before it takes hold permanently. PEP floods your body with antiretroviral drugs during that window, halting viral replication before a persistent infection can develop.
When PEP Is Appropriate
PEP is strictly for emergencies. It’s designed for situations where you may have been exposed to HIV through a specific, identifiable event: unprotected sex with someone who has or might have HIV, a condom breaking, sharing needles, or a needlestick injury in a healthcare setting. Sexual assault is another common reason people seek PEP.
PEP is not meant for people who face ongoing, repeated exposure to HIV. If that describes your situation, PrEP (pre-exposure prophylaxis) is the more appropriate option. PrEP is taken on a continuous schedule, either as a daily pill or as an injection every two to six months, to provide ongoing protection. PEP, by contrast, is a one-time emergency course.
The 72-Hour Window
The clock starts at the moment of exposure. PEP must be initiated within 72 hours, but sooner is always better. The medications work by intercepting the virus before it can replicate and spread through your immune cells, so the less time the virus has to establish itself, the more effective PEP will be. If you think you’ve been exposed, don’t wait to see how you feel. Go to an emergency room, urgent care clinic, or contact a healthcare provider as quickly as possible.
What the Treatment Looks Like
A PEP course lasts 28 days. The current CDC-recommended regimens for most adults and adolescents involve a combination of antiretroviral drugs, typically taken as one or two pills per day. The preferred options combine multiple antiviral agents into as few doses as possible to make the course easier to complete.
Completing the full 28 days is critical. In a study of people offered PEP for high-risk sexual exposures in rural Kenya and Uganda, 85% finished the entire course, and none of them contracted HIV. Skipping doses or stopping early gives the virus an opening to establish itself.
Side Effects During the 28 Days
Most people tolerate PEP well, though side effects are common enough that you should expect them. The most frequently reported ones are nausea, diarrhea, fatigue, vomiting, and headache. A meta-analysis of 24 PEP-related studies confirmed these as the top complaints. For most people, these symptoms are mild and either resolve on their own or can be managed with simple over-the-counter remedies.
Less commonly, PEP medications can cause more serious problems like liver issues or a buildup of lactic acid in the blood. These are rare but worth knowing about. If you develop symptoms that feel more severe than a mild stomach upset, particularly yellowing skin, unusual muscle pain, or difficulty breathing, that warrants medical attention.
Follow-Up Testing
Taking PEP doesn’t end with the last pill. You’ll need HIV testing at 30 days and again at 90 days after starting the course. These follow-up tests confirm whether the treatment worked. Your provider may also stay in contact during the 28-day treatment period, either by phone or clinic visits, to help you stay on track with the medication and address any side effects that might tempt you to stop early.
Where to Get PEP and How to Pay
Emergency rooms are the most reliable place to access PEP quickly, especially outside of business hours. Urgent care clinics, sexual health clinics, and some primary care offices can also prescribe it. The HIV.gov services locator can help you find nearby providers.
Cost can be a concern, but options exist. Most private insurance plans cover PEP. If you don’t have insurance or your plan doesn’t cover the specific medications, pharmaceutical patient assistance programs can provide them at no or low cost. Co-payment assistance programs are also available for people who have insurance but face high out-of-pocket costs. State-level programs, including the Ryan White HIV/AIDS Program and AIDS Drug Assistance Programs, offer additional support. Keep in mind that drug assistance programs typically cover the medication itself but not the provider visit or lab tests needed to get the prescription.