HIV Prevention

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Post-Exposure Prophylaxis (PEP)

Last Reviewed: May 25, 2018

Key Points

  • Post-exposure prophylaxis (PEP) involves taking HIV medicines very soon after a possible exposure to HIV to prevent becoming infected with HIV.
  • PEP is intended for emergency situations. It is not meant for regular use by people who may be exposed to HIV frequently.
  • PEP must be started as soon as possible to be effective and always within 72 hours (3 days) after a possible exposure to HIV.
  • PEP involves taking HIV medicines every day for 28 days.

What is PEP?

PEP stands for “post-exposure prophylaxis.” The word “prophylaxis” means to prevent or protect from an infection or disease. PEP involves taking HIV medicines very soon after a possible exposure to HIV to prevent becoming infected with HIV.

There are 2 types of PEP: oPEP and nPEP.

  • oPEP stands for “occupational post-exposure prophylaxis.” It’s when a health care worker takes PEP because of a possible exposure to HIV while working, such as from a needlestick injury.
  • nPEP stands for “non-occupational post-exposure prophylaxis.” It’s when someone takes PEP because of a possible exposure to HIV that happened outside of the person’s work, such as during sex or injection drug use.

Who should consider taking PEP?

PEP might be prescribed for you if you are HIV negative or don’t know your HIV status, and in the last 72 hours you:

  • Think you were exposed to HIV during your work, for example from a needlestick injury 
  • Think you were exposed to HIV during sex
  • Shared needles or drug preparation equipment (“works”)
  • Were sexually assaulted

Your health care provider will help to determine whether you should receive PEP.

PEP is intended for emergency situations. It is not meant for regular use by people who may be exposed to HIV frequently. Another HIV prevention method, called pre-exposure prophylaxis or PrEP, is when people at high risk for HIV take a specific HIV medicine daily to prevent getting HIV. For more information on PrEP, see the AIDSinfo fact sheet on Pre-Exposure Prophylaxis (PrEP).

What should I do if I think I was recently exposed to HIV?

If you think you were exposed to HIV, contact your health care provider immediately or go to an emergency room, urgent care clinic, or local HIV clinic right away. You will have an HIV test and other tests done. Your health care provider or emergency room doctor will help to decide whether you should receive PEP.

When should PEP be taken?

PEP must be started as soon as possible to be effective and always within 72 hours (3 days) after a possible exposure to HIV. According to research, PEP will most likely not prevent HIV infection if it is taken 72 hours after a person is exposed to HIV.

How long is PEP taken for?

PEP involves taking HIV medicines every day for 28 days. You will need to return to your health care provider at certain times while taking PEP and after you finish taking PEP for HIV testing and other tests.

What HIV medicines are used for PEP?

The Centers for Disease Control and Prevention (CDC) provides information on recommended HIV medicines for PEP. CDC also provides PEP recommendations for specific groups of people, including children, pregnant women, and people with kidney problems. The most recent PEP recommendations can be found on CDC’s PEP Guidelines webpage. Your health care provider or emergency room doctor will determine which medicines you should take as part of PEP.

Does PEP work?

PEP is effective in preventing HIV infection when it’s taken correctly, but it’s not 100% effective. The sooner you start PEP after a possible HIV exposure, the better. While taking PEP, it’s important to keep using other HIV prevention methods, such as using condoms with sex partners and using only new, sterile needles when injecting drugs. Read this fact sheet from CDC for information on how to use condoms correctly

Does PEP cause side effects?

The HIV medicines used for PEP may cause side effects. The side effects can be treated and aren’t life threatening. Talk to your health care provider if you have any 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). Because of potential drug interactions, it’s important to tell your health care provider about any other medicines that you take.

How can I learn more about PEP?

Visit the CDC websites below to learn more about PEP. This fact sheet is based on information from these sources:

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