What is PEP?

PEP stands for post-exposure prophylaxis. The word “prophylaxis” means to prevent or control the spread of an infection or disease. PEP means taking HIV medicines within 72 hours after a possible exposure to HIV to prevent becoming infected with HIV.

PEP should be used only in emergency situations. It is not meant for regular use by people who may be exposed to HIV frequently. PEP is not intended to replace regular use of other HIV prevention methods, such as consistent use of condoms during sex or pre-exposure prophylaxis (PrEP). PrEP is when people at high risk for HIV take a specific HIV medicine daily to prevent getting HIV. For more information, see the AIDSinfo fact sheets on The Basics of HIV Prevention and Pre-Exposure Prophylaxis (PrEP).

Who should consider taking PEP?

If you think you were 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:

  • Think you may have been exposed to HIV during sex
  • Shared needles or drug preparation equipment (works)
  • Were sexually assaulted

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

In addition, PEP may be prescribed for a health care worker following a possible exposure to HIV at work, for example, from a needlestick injury.

When should PEP be started?

PEP must be started within 72 hours (3 days) after a possible exposure to HIV. The sooner you start PEP after a possible HIV exposure, the better. According to research, PEP will most likely not prevent HIV infection if it is started more than 72 hours after a person is exposed to HIV.

How long is PEP taken for?

If you are prescribed PEP, you will need to take the 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 guidelines on recommended HIV medicines for PEP. The CDC guidelines include recommendations for specific groups of people, including adults and adolescents, children, pregnant women, and people with kidney problems. The most recent PEP recommendations can be found on CDC’s PEP resources webpage.

Your health care provider or emergency room doctor will work with you to determine which medicines to take for PEP.

How well 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 in some people. The side effects can be treated and aren’t life-threatening. If you are taking PEP, 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.