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Guides / PrEP and PEP

How soon do you need PEP after a possible HIV exposure?

By Bud

Not medical advice. This guide is written from CDC and public health guidance and hasn’t been reviewed by a clinician yet. Sources checked . For advice about your own health, talk to a doctor or clinic. How we write guides · Health disclaimer

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Photo by insung yoon on Unsplash.

The short answer: start PEP as soon as possible, and no later than 72 hours after a possible HIV exposure. The sooner you start, the better it works. You take it every day for 28 days, and you can get it at an emergency room, urgent care, sexual health clinic or your doctor.

If the condom broke, you bottomed raw with someone whose status you don’t know, or something happened that you didn’t agree to, this is the page. Don’t wait for a test. A test today can’t tell you whether you were infected last night, but PEP can stop it.

Do you need PEP?

When PEP is usually recommended
What happenedPEP?
You bottomed or topped without a condom (or it broke) with someone who has HIV and isn’t undetectable, or whose status you don’t knowYes, go today
You were sexually assaultedYes, go today
You shared needles or worksYes, go today
You sucked or got sucked without a condomVery low risk. A clinician can help you decide
Your partner has HIV and an undetectable viral loadUsually not needed. Undetectable means untransmittable
You take PrEP as prescribedUsually not needed. Tell the clinic if you missed doses
Based on the CDC’s 2025 guidelines on HIV postexposure prophylaxis.

Not sure? Go anyway and let them decide. Nobody at a clinic is going to judge you for asking.

Where to get PEP tonight

Time matters more than where you go.

  • Emergency room: open 24/7 and the surest bet at night or on a weekend. Say “I need PEP for a possible HIV exposure.” They can give you a starter pack.
  • Urgent care: often faster than an ER. Call first and ask if they have PEP in stock.
  • Sexual health clinic or health department: great on a weekday, and often free. Find one at locator.hiv.gov.
  • Your doctor or PrEP provider: some will call in a prescription the same day.

If you were assaulted, an ER can also collect evidence if you want that, and you can call RAINN’s free, confidential hotline at 800-656-4673 any time.

What the 28 days look like

The CDC’s preferred PEP for most adults is one pill a day (Biktarvy) or a two-pill combination. Take it at the same time every day for all 28 days. Missing doses makes it less likely to work. Most people feel fine, and some get mild nausea or tiredness for the first few days.

You’ll get an HIV test when you start and follow-up tests about 4 to 6 weeks and 12 weeks after the exposure. Get tested for syphilis, chlamydia and gonorrhea as well, from your throat and ass if that’s where the action was. Those tests usually work about 2 weeks after sex, so your follow-up visit is a good time.

How to pay for PEP

  • Insurance and Medicaid: usually cover PEP and the tests.
  • No insurance: drug makers run patient assistance programs that can cover the pills, often within a day. Ask the clinic or ER social worker to help you apply.
  • After a sexual assault: your state’s crime victim compensation program can pay for PEP and related care.

After PEP: think about PrEP

If you’re getting PEP more than once, or you keep having sex where it could happen again, PrEP is built for you. The CDC recommends going straight from PEP to PrEP without a gap, if your last HIV test is negative.

Frequently asked questions

Is 72 hours too late for PEP?
72 hours is the cutoff. Within that window, start as soon as you can. Past 72 hours, PEP isn’t recommended, but you should still test and talk to a clinic.

How effective is PEP?
PEP is very effective when you start it quickly and take every dose for 28 days. It isn’t 100%, which is why the follow-up tests matter.

Can I get PEP over the counter?
No. You need a prescription. An ER, urgent care, clinic or doctor can give you one.

Should I test for HIV right after the exposure?
Yes, at your PEP visit. That test checks that you didn’t already have HIV before the exposure. It can’t show an infection from last night yet.

Sources: CDC HIV PEP guidelines (2025).

This guide is general information, not medical advice. Talk to a doctor or clinic about your own situation. Health disclaimer

Not sure when to test? The STI test window calculator works out when each test can pick up an infection after sex.