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HIV Prevention

Post-Exposure Prophylaxis (PEP)

Last Reviewed: September 16, 2020

Key Points

  • Post-exposure prophylaxis (PEP) means taking HIV medicines within 72 hours after a possible exposure to HIV to prevent HIV infection.
  • 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 must be started within 72 hours (3 days) after a possible exposure to HIV. The sooner PEP is started after a possible HIV exposure, the better.
  • If you are prescribed PEP, you will take HIV medicines every day for 28 days.

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 HIV infection.

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 risk for HIV take a specific HIV medicine daily to prevent getting HIV. For more information, see the ClinicalInfo fact sheets on The Basics of HIV Prevention and Pre-Exposure Prophylaxis (PrEP).

Who should consider taking PEP?

PEP may be prescribed for people who are HIV negative or don’t know their HIV status, and in the last 72 hours:
  • May have been exposed to HIV during sex
  • Shared needles or other equipment (works) to inject drugs
  • Were sexually assaulted

If you think you were recently exposed to HIV, talk to your health care provider or an emergency room doctor about PEP right away.

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. A health care worker who has a possible exposure to HIV should seek medical attention immediately.

When should PEP be started?

PEP must be started within 72 hours (3 days) after a possible exposure to HIV. The sooner PEP is started 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.

If you are prescribed PEP, you will need to take the HIV medicines every day for 28 days.

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 PEP is started 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.

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.