HIV Prevention

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 (3 days) after a possible exposure to HIV to prevent 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 and proper use of condoms during sex or pre-exposure prophylaxis (PrEP). PrEP is different than PEP, in that people at risk for HIV take a specific HIV medicine daily or an injection every two months to prevent getting HIV.

For more information, see the HIVinfo fact sheets on The Basics of HIV Prevention and Pre-Exposure Prophylaxis (PrEP).

PEP may be prescribed for people who are HIV negative or do not know their HIV status, and who 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
• May have been exposed to HIV at work (occupational exposure)

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

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

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. Every hour counts. 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.

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.

PEP is effective in preventing HIV when it is taken correctly, but it is not 100% effective. The sooner PEP is started after a possible HIV exposure, the better. Every hour counts. The exact effectiveness of PEP is difficult to measure, but observational research suggests that PEP can reduce the risk of getting HIV by more than 80%. The effectiveness is highly dependent on adherence (taking PEP every day for 28 days) and in the case of non-occupational exposure, no further exposures to HIV. Effectiveness is likely much higher than 80% if PEP is used consistently and correctly, as prescribed.

While taking PEP, it is important to keep using other HIV prevention methods, such as consistently and properly using condoms with sex partners and using only new, sterile needles and syringes when injecting drugs.

The HIV medicines used for PEP may cause side effects in some people. The side effects can be treated and are not 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.

From CDC:

• Preventing HIV With PEP
• PEP Resources
• PEP and Workplace Exposures

Also see the HIV Source collection of HIV links and resources.