If you've just had unprotected sex and you're worried about HIV, the single most time-sensitive step is to ask a clinician about PEP (post-exposure prophylaxis) — HIV medicine that can stop the virus from taking hold if you start it within 72 hours CDC, PEP. Go to an ER or urgent care today, then plan your testing afterward.
sooner is better — every hour counts
taken daily
not a substitute for PrEP
| Item | Value |
|---|---|
| Start within | 72 hours — sooner is better — every hour counts |
| Course | 28 days — taken daily |
| Use | emergencies — not a substitute for PrEP |
| Where | ER / urgent care |
The essentials: your first 72 hours
After a possible HIV exposure, time is the variable you can't get back. PEP only works if it's started within 72 hours (3 days) of the exposure — after that window it's no longer effective. The clock starts at the moment of the encounter, not at the moment you started worrying about it, so even if you've already lost a day, every remaining hour still counts.
PEP is for emergencies — situations like a condom breaking during sex, sharing needles or injection equipment, or a sexual assault. It's not something you take after the fact for routine peace of mind, and it isn't a once-and-done fix for ongoing risk. If you find yourself reaching for PEP repeatedly, that's a signal to ask about PrEP, a daily preventive medicine designed for people with continuing exposure.
- Treat it as a same-day errand. Call a health care provider, head to an emergency room, or visit urgent care right now — including if the exposure happened at work (for example, a needlestick for a health worker).
- Say plainly that you may have been exposed to HIV and ask about PEP. Use those words so you're triaged for the time-sensitive issue it is.
- Don't let cost stall the start. Ask about patient-assistance programs, and let the medicine begin while any paperwork gets sorted out.
- Once you've handled the PEP question, mark your calendar for testing — the right windows come later, not today.
How PEP actually works
HIV doesn't infect the body instantly. After exposure, the virus needs time to enter cells, copy itself, and spread into a self-sustaining infection. PEP is a combination of antiretroviral drugs — the same kinds used to treat HIV — that block that early replication so the virus can't establish a foothold before your immune system and the medicine clear it.
That biology is exactly why the 72-hour limit is firm and why sooner is dramatically better. The longer the virus has to dig in, the less chance the medicine has of cutting it off. Starting within hours gives PEP the best shot; waiting until day three is far less reliable, which is the whole reason clinicians treat this as an urgent, same-day matter rather than a wait-and-see one.
Once you're prescribed PEP, you take it every day for 28 days. Finishing the full course matters — stopping early gives any remaining virus an opening to rebound. Set reminders, and tell your provider promptly if side effects make the medicine hard to keep down so they can help rather than have you quietly quit.
Practical details: getting it, the cost, the follow-up
In real life, PEP is a focused errand: walk into an ER or urgent care, explain the exposure, and a clinician can start you the same day. You don't need a long appointment or a specialist referral — front-line providers handle this regularly. If you have a primary care doctor who can see you immediately, that works too, but don't burn precious hours waiting for an opening when an ER is open now.
Money is the most common reason people hesitate, and it's the worst reason to lose hours. There are patient-assistance programs and manufacturer support that can cover the medication; the practical move is to start the pills first and let the financial paperwork catch up. A clinician or pharmacist can point you to those programs on the spot.
PEP covers HIV — and only HIV. It does nothing for chlamydia, gonorrhea, syphilis, hepatitis, or other infections you might have been exposed to during the same encounter. Those need their own plan, which means testing on the correct schedule rather than today. Here's how the pieces fit together:
| Concern | What to do | Timing |
|---|---|---|
| HIV (with a real exposure) | Ask about PEP at an ER, urgent care, or clinic | Within 72 hours — same-day, every hour counts |
| Pregnancy (after unprotected vaginal sex) | Ask a pharmacist or clinician about emergency contraception | The sooner the better after sex |
| Other STIs (chlamydia, gonorrhea, syphilis, etc.) | Plan — see the testing windows and get tested | Later, once enough time has passed to detect them |
Testing too early gives false reassurance because infections need time to become detectable. For the full schedule of what to check and when, see our guide on std testing after unprotected sex and the detailed breakdown of when to test after exposure. When the timing is right, you can get tested for the full panel.
What PEP does not cover
PEP is not birth control. If pregnancy is a concern after unprotected vaginal sex, emergency contraception is a separate, time-sensitive question — ask a pharmacist or clinician the same day, since it also works best taken early.
PEP is also not a long-term prevention strategy. If your exposures keep happening — a regular partner whose status is unknown, ongoing injection-drug risk — repeatedly scrambling for PEP is the wrong tool. PrEP, taken before exposures, is designed for exactly that situation CDC, PrEP. And because earlier hiv treatment can help prevention, knowing a partner's status and treatment also changes the math on your risk.
When to see a clinician right away
Don't wait if any of these apply — go today, not tomorrow:
- A condom broke or slipped during sex with a partner whose HIV status you don't know or who is HIV-positive and not on treatment.
- You shared needles, syringes, or other injection equipment.
- You were sexually assaulted — an ER can address PEP, emergency contraception, injuries, and evidence in one visit.
- You had an occupational exposure at work, such as a needlestick.
If it's been more than 72 hours, PEP is no longer the path — but a clinician can still help you with testing, emergency contraception if relevant, and ongoing prevention like PrEP. The conversation is still worth having.