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What are 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. It can either be a pill that you take every day or an injection that you get every two 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 (pre-exposure prophylaxis)
Who should consider taking PrEP?
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 disease in the past 6 months
- You inject drugs and:
- Share needles or other equipment to inject drugs OR
- Have an injection partner with HIV
- You have been prescribed PEP and:
- 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 baby from getting HIV infection while you try to get pregnant, during pregnancy, or while breastfeeding.
How well does PrEP work?
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 STDs, 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 health care provider. If you are having trouble taking PrEP every day or if you want to stop taking PrEP, talk to your provider.
Does PrEP cause side effects?
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.
PEP (post-exposure prophylaxis)
Who should consider taking PEP?
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, OR
- 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.
When should I start PEP and how long do I need to take it?
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.
Does PEP cause side effects?
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.
Can I take PEP every time I have unprotected sex?
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.
- Post-Exposure Prophylaxis (PEP) (National Institutes of Health, Office of AIDS Research) Also in Spanish
- Pre-Exposure Prophylaxis (PrEP) (National Institutes of Health, Office of AIDS Research) Also in Spanish
- Pre-Exposure Prophylaxis (PrEP) (HIV.gov; National Institutes of Health, Office of AIDS Research)
- What Is PEP? (National Library of Medicine) - PDF Also in Spanish
- What Is PrEP? (National Library of Medicine) - PDF Also in Spanish
- All About PrEP! (Greater Than AIDS)
- Black Women and PrEP (Black AIDS Institute)
- PrEP vs. PEP (National Institutes of Health, Office of AIDS Research) Also in Spanish
- ClinicalTrials.gov: PEP (Post-Exposure Prophylaxis) (National Institutes of Health)
- ClinicalTrials.gov: PrEP (Pre-Exposure Prophylaxis) (National Institutes of Health)
Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)
- Article: Risk-based versus universal PrEP delivery during pregnancy: a cluster randomized trial...
- Article: Clinic-Integrated Smartphone App (JomPrEP) to Improve Uptake of HIV Testing and...
- Article: An open-label evaluation of safety and tolerability of coformulated bictegravir/emtricitabine/tenofovir alafenamide...
- HIV: PrEP and PEP -- see more articles
- Glossary (HIV.gov; National Institutes of Health, Office of AIDS Research)
Find an Expert
- Find a Provider (PleasePrEPMe) Also in Spanish
- PrEP for Women (The Well Project)
- PrEP 101 (Centers for Disease Control and Prevention) - PDF - In English and Spanish