PEP is post-exposure prophylaxis: HIV medication taken after a possible exposure to prevent HIV from taking hold. It must start within 72 hours, ideally within 24, and is taken daily for 28 days. Get it from an emergency room, urgent care, sexual health clinic, or your provider. Exposure to HIV is treated as a medical emergency.
The 72-hour window
CDC is unambiguous: PEP is medicine that prevents HIV after a possible exposure, PEP is for emergency situations only, and PEP must be started within 72 hours (3 days) after a recent possible exposure to HIV. The sooner you start, the better — every hour counts.[1]
Federal guidance narrows the target further. CDC's 2025 recommendations direct health care professionals to ensure the first dose is provided as soon as possible, and ideally within 24 hours, but no later than 72 hours after exposure. Available clinical evidence suggests the shorter the time from exposure to initiation, the greater the likelihood of preventing HIV acquisition.[2]
Two operational details save time in a real emergency. The initial dose should not be delayed due to pending results of any laboratory-based testing, and the first dose should be administered as soon as possible during the initial encounter.[2] The guidance states plainly that exposure to HIV is a medical emergency.[2]
When you need it
CDC lists the situations where PEP may be needed: during sex — for example, if a condom broke — through sharing needles, syringes, or other equipment to inject drugs, or if you've been sexually assaulted.[1]
Federal guidance frames eligibility clinically: a 28-day course is recommended for people without HIV who seek care within 72 hours after a nonoccupational exposure to blood, genital secretions, or other potentially infectious body fluids of someone known to have HIV or of unknown HIV status, when that exposure represents a substantial risk for HIV acquisition.[2]
For workplace exposures, CDC directs people to see a provider, an emergency room doctor, or an urgent care provider right away, report the exposure to the appropriate person at work, and seek medical attention immediately. Clinicians can call the PEPline at 1-888-448-4911 for advice on managing occupational exposures, and exposed workers may also call — after seeking local care first.[1]
If a partner living with HIV is on treatment with a sustained undetectable viral load, that changes the calculus: CDC's evidence review found no risk of sexual transmission from people who get and keep an undetectable viral load.[3] Bring that information to the visit; it may mean PEP is not needed.
The 28-day course and what it involves
If you're prescribed PEP, you'll need to take it daily for 28 days.[1] Federal guidance confirms the recommended course is 28 days using a newer-generation three-drug antiretroviral regimen.[2]
On effectiveness, the guidance is honest about the evidence base: no randomized, placebo-controlled clinical trial of nPEP efficacy has been performed, and there are no FDA-approved medications specifically for nPEP. What the accumulated evidence does show is that nPEP, when used as currently recommended — a 72-hour initiation window, a 28-day duration, and a newer-generation three-drug regimen — is safe, generally well tolerated, and likely to reduce the risk for HIV acquisition. Available data indicate nPEP is highly effective when taken as prescribed.[2]
Side effects with modern regimens are generally mild and manageable, and the guidance describes the recommended course as generally well tolerated. Finish all 28 days — an incomplete course is the main reason PEP fails.
If PEP keeps coming up in your life, that is a signal rather than a failure. CDC notes PrEP can help protect people who have been prescribed PEP and report continued risk behavior, or who have used multiple courses of PEP.[4] Many clinicians transition people directly from finishing PEP onto PrEP.
Testing continues after the course ends, and the timelines are worth knowing. A laboratory antigen/antibody test using blood from a vein can usually detect HIV 18 to 45 days after exposure, a nucleic acid test 10 to 33 days, and antibody tests 23 to 90 days.[7] Your clinician will schedule follow-up testing on that basis rather than at a single arbitrary date.
Florida angle: where to go tonight
In Florida, the fastest routes to PEP are a hospital emergency department, an urgent care center, or a county health department sexual health clinic — CDC's guidance is to talk right away to a health care provider, an emergency room doctor, or an urgent care provider.[1] The Florida Department of Health maintains a statewide PrEP and PEP resource page, and county health department clinics across the state provide both.[5] If you need testing alongside PEP, Florida has more than 1,600 publicly funded and registered HIV testing sites.[6] Do not wait for an appointment to open up — the clock is 72 hours, and every hour counts.
Related questions
What if it has been more than 72 hours?
PEP is no longer expected to work, but you should still be seen. Federal guidance addresses people who seek care beyond 72 hours, and a clinician can arrange baseline and follow-up HIV testing, evaluate you for other sexually transmitted infections, and start you on PrEP so you are protected going forward.
How much does PEP cost?
It varies by where you go, and cost should not stop you. Emergency departments, urgent care, and county health department clinics all handle PEP, and many clinics have starter packs or assistance programs. Ask about financial assistance at the visit rather than delaying care to price-shop — the window is only 72 hours.
Will PEP make me sick?
Modern three-drug PEP regimens are described in federal guidance as safe and generally well tolerated. Some people have nausea, fatigue, or headache in the first days. Tell the prescriber if side effects are making it hard to finish, because completing all 28 days is what determines whether PEP works.
Should I be on PrEP instead?
If possible exposures are recurring, yes. CDC specifically notes PrEP can help protect people who have been prescribed PEP and report continued risk, or who have used multiple courses of PEP. Many providers move patients straight from the last PEP dose onto PrEP so there is no gap in protection.
Related from RiseUpToHIV
References & Sources
- CDC — Preventing HIV with PEP. States PEP must start within 72 hours, every hour counts, is taken daily for 28 days, lists qualifying exposures, workplace guidance and the PEPline number, and directs people to providers, emergency rooms, or urgent care.. ↩ ↩ ↩ ↩ ↩
- CDC MMWR — Antiretroviral Postexposure Prophylaxis After Sexual, Injection Drug Use, or Other Nonoccupational Exposure to HIV. Directs first dose ideally within 24 hours and no later than 72 hours, no delay for labs, states HIV exposure is a medical emergency, defines the 28-day three-drug course, and describes the efficacy evidence base.. ↩ ↩ ↩ ↩ ↩ ↩
- CDC — HIV Treatment as Prevention. States studies have shown no risk of sexual transmission from people who get and keep an undetectable viral load.. ↩
- CDC — Preventing HIV with PrEP. States PrEP can help protect people who have been prescribed PEP and report continued risk behavior or have used multiple courses of PEP.. ↩
- Florida Department of Health — PrEP and PEP. State resource page for PrEP and PEP services and materials in Florida.. ↩
- Florida Department of Health — HIV Prevention. States Florida has over 1,600 publicly funded and registered HIV testing sites statewide.. ↩
- CDC — HIV Testing. Gives detection windows of 18 to 45 days for laboratory antigen/antibody tests using venous blood, 10 to 33 days for nucleic acid tests, and 23 to 90 days for antibody tests.. ↩
Community publications like POZ, Positively Aware, and TheBody inform framing and lived-experience context on RiseUpToHIV. Every clinical, epidemiological, or public-health claim above is anchored to a primary source.