Health Topic

HIV: PrEP and PEP

PrEP (pre-exposure prophylaxis) and PEP (post-exposure prophylaxis) are medicines to prevent HIV. They are prescribed before or after there is exposure to HIV.

Reviewed Reviewed by a registered pharmacistGeneral information

Also called: Post-Exposure Prophylaxis · Pre-Exposure Prophylaxis

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About HIV: PrEP and PEP

PrEP and PEP are medicines to prevent HIV. Each type is used in a different situation:

  • PrEP stands for pre-exposure prophylaxis. It is for people who don't already have HIV but are at risk of getting it. PrEP is medicine that can reduce this risk. You can take it as a pill every day or as an injection every two or six months. With PrEP, if you do get exposed to HIV, the medicine can stop HIV from taking hold and spreading throughout your body.
  • PEP stands for post-exposure prophylaxis. PEP is for people who have possibly been exposed to HIV. It is only for emergency situations. PEP must be started within 72 hours after a possible exposure to HIV.

PrEP can help protect you if you don't have HIV and any of these applies to you:

  • You have had anal or vaginal sex in the past 6 months and: Have a sexual partner with HIV,
  • Have not consistently used a condom, OR
  • Have been diagnosed with a sexually transmitted infection (STI) in the past 6 months
  • Share needles or other equipment to inject drugs OR
  • Have an injection partner with HIV
  • Continue engaging in high-risk behaviors OR
  • Have used multiple courses of PEP

If you have a partner who is HIV-positive and are considering getting pregnant, talk to your health care provider about PrEP. Taking it may help protect you and your fetus or baby from getting an HIV infection while you try to get pregnant, during pregnancy, or while breastfeeding.

PrEP is very effective when you take it consistently. It reduces the risk of getting HIV from sex by about 99%. In people who inject drugs, it reduces the risk of HIV by at least 74%. PrEP is much less effective if you do not take it consistently.

PrEP does not protect against other STIs, so you should still use latex condoms every time you have sex. If your or your partner is allergic to latex, you can use polyurethane condoms.

You must have an HIV test every 3 months while taking PrEP, so you'll have regular follow-up visits with your provider. If you are having trouble taking PrEP every day or if you want to stop taking PrEP, talk to your provider.

Some people taking PrEP may have side effects, like nausea. The side effects are usually not serious and often get better over time. If you are taking PrEP, tell your provider if you have a side effect that bothers you or that does not go away.

If you are HIV-negative and you think you may have been recently exposed to HIV, contact your health care provider immediately or go to an emergency room right away.

You may be prescribed PEP if you are HIV negative or don't know your HIV status, and in the last 72 hours you may have been exposed to HIV:

  • During sex, for example if a condom broke during sex with someone who could have HIV,
  • Through the sharing of needles or drug preparation equipment
  • Through sexual assault

Your provider or emergency room doctor will help to decide whether PEP is right for you.

PEP may also be given to a health care worker after a possible exposure to HIV at work, for example, from a needlestick injury.

PEP must be started within 72 hours (3 days) after a possible exposure to HIV. The sooner you start it, the better; every hour counts.

You need to take the PEP medicines every day for 28 days. You will have to see your provider at certain times during and after taking the PEP, so you can have an HIV screening test and other testing.

Some people taking PEP may have side effects, like nausea. The side effects are usually not serious and often get better over time. If you are taking PEP, tell your provider if you have a side effect that bothers you or that does not go away.

PEP medicines may also interact with other medicines that a person is taking (called a drug interaction). So it's important to tell your provider about any other medicines that you take.

PEP is only for emergency situations. It is not the right choice for people who may be exposed to HIV frequently - for example, if you often have sex without a condom with a partner who is HIV-positive. In that case, you should talk to your health care provider about whether PrEP (pre-exposure prophylaxis) would be right for you.

It sits within Infections, Immune System and Drug Therapy.

The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on HIV: PrEP and PEP

11 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

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Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Post-Exposure Prophylaxis, Pre-Exposure Prophylaxis. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for HIV: PrEP and PEP, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.