HomeHealth TopicsInfectionsHIV: PrEP and PEP
Back to Infections
HIV: PrEP and PEP
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Infections

HIV: PrEP and PEP

PrEP and PEP are vital medical interventions used to prevent HIV infection, either as a daily preventative measure or as an emergency response after potential exposure.

What are PrEP and PEP?

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

  • PrEP (pre-exposure prophylaxis) is for people who don't already have HIV but are at risk of getting it. It can be taken as a daily pill or an injection every two or six months to stop HIV from taking hold and spreading throughout your body.
  • PEP (post-exposure prophylaxis) is for people who have possibly been exposed to HIV. It is only for emergency situations and must be started within 72 hours after a possible exposure.

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 an STI in the past 6 months.
  • You inject drugs and share needles 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 an HIV-positive partner and are considering pregnancy, talk to your health care provider about how PrEP may protect you and your fetus or baby.

How well does PrEP work?

PrEP is very effective when taken consistently, reducing the risk of getting HIV from sex by about 99% and by at least 74% in people who inject drugs. It does not protect against other STIs, so you should still use condoms. You must have an HIV test every 3 months while taking PrEP.

Does PrEP cause side effects?

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

Who should consider taking PEP?

If you are HIV-negative and think you may have been recently exposed to HIV, contact your health care provider or go to an emergency room immediately. You may be prescribed PEP if you were exposed within the last 72 hours through:

  • Sex (e.g., a broken condom with someone who could have HIV)
  • Sharing needles or drug preparation equipment
  • Sexual assault
  • Workplace exposure (e.g., 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; the sooner, the better. You must take the medicine every day for 28 days and see your provider for follow-up HIV screening and testing.

Does PEP cause side effects?

Side effects like nausea may occur but are usually not serious. Because PEP medicines may interact with other drugs, it is important to tell your provider about any other medications you are taking.

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. In those cases, you should talk to your health care provider about whether PrEP would be right for you.

Frequently Asked Questions

You should not take PrEP and PEP simultaneously without specific medical guidance. If you are already taking PrEP consistently and have a potential exposure, your healthcare provider may advise you to continue your PrEP regimen or switch to a PEP regimen depending on the specific drugs involved and the nature of the exposure. If you are not currently on PrEP and have a recent exposure, PEP is the immediate priority. Always consult a clinician immediately after an exposure to determine the correct protocol, as mixing regimens incorrectly can reduce effectiveness or increase side effects.
Full protection depends on the type of sex and the formulation of PrEP. For oral daily PrEP, you are generally considered fully protected after 7 days of consistent daily use for vaginal sex and after 21 days for anal sex. This is because the drug needs time to reach sufficient concentrations in the rectal and vaginal tissues. If you are using long-acting injectable PrEP, protection begins shortly after the first injection, but you should discuss the specific timeline with your provider to ensure you are covered before engaging in high-risk activities.
PEP is highly effective when started within 72 hours and taken for the full 28-day course, but it is not 100% guaranteed. Signs that PEP may not be working include developing flu-like symptoms such as fever, rash, or swollen lymph nodes two to four weeks after the exposure. You should get an HIV test at 4 weeks after the exposure and again at 12 weeks (or 3 months) to confirm that you have not contracted the virus. If you experience severe side effects from the medication, contact your healthcare provider immediately for management options.
If you miss a dose, take it as soon as you remember unless it is close to the time for your next scheduled dose. Do not double up on doses. Consistency is key for maximum efficacy, but missing a single dose does not mean you have lost all protection. However, if you have missed multiple doses or have been inconsistent, consider using condoms or other barrier methods until you have taken the medication consistently for at least 7 days (for vaginal sex) or 21 days (for anal sex) to ensure full viral suppression in relevant tissues.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

kontakt@hittavard.se

Ⓒ 2024. Alla rättigheter förbehålls av juxt ab

Sök
Om ossVillkor och policyVanliga frågorKontakta oss