PrEP vs PEP: Use, Timing, and Follow-Up
PrEP is used before possible HIV exposure; PEP is used after an emergency exposure. Both are for people who do not have HIV, but their dosing, tests…
อ่านภาษาไทย
Contents
PrEP is used before possible HIV exposure; PEP is used after an emergency exposure. Both are for people who do not have HIV, but their dosing, tests, and follow-up differ. Instructions for one regimen must not be applied to another.
PrEP
Options include daily oral PrEP, 2-1-1 dosing for some adult cisgender men who have sex with men, and long-acting injection in some countries. Time to maximum protection and stopping instructions depend on the regimen and exposure site. Daily oral PrEP reaches maximum protection at about 7 days for receptive anal sex and may take up to 21 days for receptive vaginal sex or injection drug use. There is no universal “start for 7 days and continue four weeks after sex” rule.
PEP
When indicated, PEP should start as soon as possible and no later than 72 hours. It is generally taken for 28 days. Baseline HIV testing should be prompt, but an indicated first dose should not be delayed. PEP does not make the body develop immunity; the medicines help prevent HIV from establishing infection.
Before Starting
Assessment includes HIV and possible acute symptoms, kidney function, hepatitis B, other medicines, and pregnancy as relevant. A positive result or suspected acute HIV requires assessment for ART rather than continuing PrEP or PEP independently.
Effectiveness and Side Effects
PrEP reduces sexual acquisition risk by about 99% when prescribed and used correctly. PEP greatly reduces risk when started promptly and completed, but one 70–80% figure does not apply to every event. Nausea, headache, or diarrhea can occur; contact the provider rather than stopping on your own. Neither prevents other STIs.
Verified references
Links and relevance to the article’s main topic were reviewed on 13 August 2026. Each source supports only the scope stated in the original document and does not replace personalised medical, legal, or service advice.
- CDC: Clinical Guidance for PrEP Accessed 13 August 2026
- CDC: Clinical Guidance for PEP Accessed 13 August 2026
- CDC: 2025 nPEP Guidelines Accessed 13 August 2026
