A clinician-assessed course started after a possible HIV exposure.
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PEP
Post-exposure prophylaxis: a time-sensitive course of HIV medicine assessed after a possible exposure to reduce the chance of infection.
Sexual health
In brief
Urgent HIV prevention after exposure—hours matter.
PEP is an emergency intervention, not a test result or routine substitute for PrEP. It should be assessed as soon as possible—ideally within 24 hours and no later than 72 hours after the exposure. A sexual-health clinic or A&E evaluates whether the exposure warrants treatment.
Planned prevention used before and around potential exposures.
Testing may establish baseline status but cannot immediately exclude infection from the new exposure.
Sustained undetectable viral load prevents sexual transmission and affects whether PEP is indicated.
Act without waiting
Contact a sexual-health clinic immediately, or A&E when services are closed. Do not wait for symptoms, a partner's test, or the end of a testing window before seeking assessment.
After 72 hours PEP is generally not offered because it is unlikely to work, but testing and other clinical advice still matter.
Clinical assessment
Clinicians consider the type of exposure, body site, timing, source information, viral load where known, PrEP use and other factors. Not every concern requires PEP.
The assessment may include baseline HIV and other tests, medication history, pregnancy considerations and potential drug interactions.
Course and follow-up
UK guidance generally uses a 28-day course. Complete it exactly as prescribed and contact the service about side effects, missed doses or interactions rather than stopping independently.
Follow-up testing occurs after the course according to current clinical guidance. PEP does not protect against later exposures.
After an exposure
Clinics can also discuss emergency contraception, hepatitis prevention, STI testing, assault support and future PrEP where relevant. Care should remain confidential and non-judgemental.
If exposure occurred through assault, the person can access healthcare and specialist support without deciding immediately whether to report to police.
Non-graphic examples
What the umbrella may include
- Going to A&E overnight after a possible exposure.
- Starting PEP within 24 hours after clinical assessment.
- Completing a prescribed 28-day course.
- Attending follow-up HIV testing at the advised time.
- Discussing PrEP for future ongoing exposure after PEP.
Reviewed 30 August 2026
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