Post-Exposure Prophylaxis (PEP) for HIV

Prophylaxis is a treatment that helps you prevent an infection from bacteria, fungus, a virus, or a parasite either before you come in contact with the bug or after you’ve been exposed.. Post-exposure prophylaxis, or PEP, means you take it after you may have come into contact with one of those bugs.

If you've been exposed to HIV (the virus that causes AIDS), PEP is a course of two or three drugs that will make you less likely to be infected.

With the right treatment, there's about an 80% chance the virus will be stopped. But you have to take the full course of drugs, and not everyone follows through. Only 57% of people who start the treatment typically finish it. This may be because you have to take the medication for 28 days, and it can cause side effects. It also can be expensive.

Who Might Need PEP?

PEP may help:

  • People who think they might have been exposed to HIV during sex
  • Drug users who have recently shared needles or other related items
  • Health-care workers who think they've been exposed to HIV on the job

If you think you have been exposed to HIV, a health care provider will help determine whether you need PEP.  You should seek health care as soon as possible after such an exposure.

PEP is for emergency situations only. It should not be used as a substitute for safe sex or new sterile needles.

If you're frequently exposed to HIV -- because of contact with multiple sex partners or injecting drug use, for example -- talk with your doctor about pre-exposure prophylaxis (PrEP) instead. PEP uses  more drugs than PrEP and is used for only one month..


You have to start PEP within 72 hours of exposure. After that, the treatment won't work. If you think you may have been exposed to HIV, get medical attention as soon as possible.

How It Works

The idea behind PEP is that the same drugs that treat HIV can help you fight the virus as it tries to infect you. These drugs are called antiretrovirals.


That involves a combination of three drugs. The medications used in this way keep HIV from establishing itself in your body

You'll take them once or twice a day for 28 days:

  • For adults, the Centers for Disease Control and Prevention (CDC) recommends a drug called tenofovir, combined with  emtricitabine(these two drugs are combined in one pill), and a third drug, either raltegravir or dolutegravir.
  • Women in early pregnancy, or who are sexually active and could become pregnant while taking PEP, or women who were victims of sexual assault should not take dolutegravir as part of PEP. Raltegravir should be used instead.
  • Children who need PEP, down to the age of 2, get the same drugs, but adjusted for their weight

If you're on PEP, use condoms if you have sex to lower the chances that you'll be exposed to HIV again or that you'll pass the virus to others if you are infected.

Side Effects

You might have nausea or fatigue with PEP. The drugs also can cause headache, insomnia, and diarrhea. In rare cases, they can cause serious health issues, including liver problems.


If you are prescribed PEP, your doctor will take blood specimens at the time you start and may want to get other tests, such as for sexually-transmitted diseases besides HIV.   Follow-up testing will be needed to see if you have become infected with HIV.

It's possible that if the treatment doesn't work and you become infected with HIV, the virus may be resistant to some of the HIV drugs.

WebMD Medical Reference Reviewed by Jonathan E. Kaplan, MD on September 14, 2018

Sources "Overview of HIV Treatments," "Post-Exposure Prophylaxis (PEP)."

National Institutes of Health: AIDSinfo Drug Database.

University of California San Francisco -- Center for AIDS Prevention Studies: "What Is Post-Exposure Prevention (PEP)?"

CDC: "HIV Basics: PEP."

U.S. Department of Health and Human Services: "Antiretroviral Postexposure Prophylaxis After Sexual, Injection-Drug Use, or Other Nonoccupational Exposure to HIV in the United States." January 2005.

World Health Organization: "Post-exposure prophylaxis to prevent HIV infection," December 2014.

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