HIV Prevention

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 refers to the use of HIV medicines to prevent HIV infection within 72 hours (3 days) after a possible exposure.

PEP should be used only in emergency situations and is not meant for regular use by people who may be exposed to HIV frequently. PEP is not intended to replace the 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 before an exposure occurs.

For more information, see the HIVinfo 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 do not have HIV or who 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 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. Every hour counts. According to the Centers for Disease Control and Prevention (CDC), 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 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.

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 when it is taken correctly, but it is not 100% effective. 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 additional 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 if a person injects drugs. HIV PEP does not protect against other sexually transmitted infections (STIs). Using condoms will reduce your risk of HIV and will also help protect against other STIs.

Does PEP cause side effects?

The HIV medicines used for PEP may cause side effects in some people. The common side effects are generally mild and may include diarrhea, nausea, tiredness, and headache, and can be treated or will subside on their own. Less commonly, PEP medicines can cause more serious side effects such as liver problems or lactic acidosis that may require medical attention.

Before taking PEP, be sure to consult your health care provider about any potential side effects cause by PEP medicines. If you are taking PEP, talk to your health care provider if you have any side effects that bother you or that do not go away.

What should you do after taking PEP?

Your next steps after taking PEP will depend on whether the medicine effectively prevented HIV infection.

If you test negative for HIV after a full course of PEP, you should consider taking precautionary measures to avoid getting HIV moving forward, such as taking PrEP and using condoms. See The Basics of HIV Prevention for more tips to prevent HIV.

If you test positive for HIV after taking PEP, it’s best to talk to your health care provider about the next steps. Generally, if you test positive for HIV, you will do additional testing (lab tests) before getting prescribed an HIV treatment regimen. See Just Diagnosed: Next Steps After Testing Positive for HIV for more information.

This fact sheet is based on information from the following sources:

From CDC:

• Preventing HIV with PEP
• Now’s the Time to Find Out About PrEP and PEP (PDF)

From MedlinePlus:

• HIV: PrEP and PEP

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

What is PrEP?

PrEP stands for pre-exposure prophylaxis. The word “prophylaxis” means to prevent or control the spread of an infection or disease.

Three HIV medicines are approved by the U.S. Food and Drug Administration (FDA) for use as PrEP: 

• Truvada (or a generic equivalent), a pill taken by mouth every day.
• Descovy (or a generic equivalent), a pill taken by mouth every day.
• Apretude, a shot taken every 2 months.

Which medicine to use for PrEP depends on a person’s individual situation.

PrEP works by blocking the HIV life cycle, preventing the virus from taking hold and spreading if exposed during sex or injection drug use. However, its effectiveness relies on taking the medication as prescribed to ensure there is enough medicine in the bloodstream to stop the virus from spreading.

Should I consider taking PrEP?

PrEP is used by people who do not have HIV and are at high risk of being exposed to HIV through sex or injection drug use. If you have HIV, PrEP medicine is not for you.

Specifically, the Centers for Disease Control and Prevention recommends that you should consider PrEP if you are HIV negative, have had anal or vaginal sex in the past 6 months, and:

• Have a sexual partner with HIV (especially if the partner has an unknown or detectable viral load), or
• Have not consistently used a condom, or
• Have been diagnosed with a sexually transmitted infection (STI) in the past 6 months.

PrEP is also recommended if you inject drugs and you:

• Have an injection partner with HIV, or
• Share needles, syringes, or other equipment to inject drugs.

PrEP should also be considered for people without HIV who have been prescribed non-occupational post-exposure prophylaxis (nPEP) and:

• Report continued unsafe sex practices, or
• Have used multiple courses of PEP.

If you think PrEP may be right for you, talk to your health care provider.

How well does PrEP work?

Oral PrEP is most effective when taken consistently each day. CDC reports that consistent PrEP use reduces the risk of getting HIV from sex by about 99% and from injection drug use by at least 74%.

Currently, Apretude shots are recommended for people who are at risk of getting HIV from sex. Because its effectiveness has not been evaluated for receptive vaginal sex, Descovy is not recommended for women who are at risk of getting HIV.

Although getting HIV is unlikely when taking PrEP as prescribed, it can still occur. People who get HIV while taking PrEP may acquire HIV drug resistance. People who acquire HIV drug resistance from PrEP may have fewer HIV treatment options, though a health care provider can still help identify effective options.

Adding other prevention methods, such as condom use, along with PrEP, can further reduce your risk of getting HIV.

Does PrEP cause side effects?

In some people, PrEP can cause side effects, such as nausea, diarrhea, headache, dizziness, depression, and insomnia. These side effects are not serious and generally go away over time. However, in rare cases, more serious side effects such as kidney failure and lactic acidosis can occur.

Before taking PrEP, consult with your health care provider about any potential side effects. If you are taking PrEP, tell your health care provider immediately if you have any side effects that bother you or that do not go away.

What should you do if you think that PrEP can help you?

If you think PrEP may be right for you, see a health care provider. PrEP can be prescribed only by a health care provider. If your health care provider agrees that PrEP may reduce your risk of getting HIV, the next step is an HIV test. You must have a negative HIV test immediately before starting PrEP.

How often should you take PrEP?

Oral PrEP: People taking oral PrEP (Truvada or Descovy) need to take their PrEP pills every day. This is the only CDC- and Food and Drug Administration (FDA)-recommended way to take oral PrEP for HIV prevention.

Some people may take PrEP “on demand” when they think they may acquire HIV. This method of taking PrEP for HIV prevention is not recommended by the CDC or FDA and should only be considered if it is recommended by your health care provider.

On-demand PrEP relies on a “2-1-1” schedule, in which you take two pills 2 to 24 hours before sex, one pill 24 hours after the first dose, and another pill 24 hours after the second dose.

Injectable PrEP: If you are taking Apretude, do not miss any injections (every two months). PrEP is much less effective when it is not taken as prescribed, which increases your risk of getting infected with HIV and acquiring HIV drug resistance.

What else should you know about PrEP?

Continue to use condoms while taking PrEP. Even though daily PrEP can greatly reduce your risk of HIV, it does not protect against other STIs, such as gonorrhea and chlamydia. Combining condom use with PrEP will further reduce your risk of HIV, as well as protect you from other STIs.  

If you inject drugs, avoid sharing needles or other drug injection equipment with other people. Although HIV PrEP reduces the risk of transmission from injection drug use, the risk of getting HIV remains much higher from injecting drugs than from sex.

You must also take an HIV test every 3 months while taking PrEP, so you will have regular follow-up visits with your health care provider. If you are having trouble taking PrEP as scheduled or if you want to stop taking PrEP, talk to your health care provider.

If you do become HIV positive, you will need to take other medicines to treat HIV. PrEP medications and protocols are not approved for treatment of people with HIV.

This fact sheet is based on information from the following sources:

From CDC: 

• Preventing HIV with PrEP
• PrEP Medication Guide: Reduce Your Risk of Getting HIV
• Now’s the Time to Find Out About PrEP and PEP

From DailyMed:

• Truvada
• Descovy
• Apretude

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

How is HIV transmitted?

The person-to-person spread of human immunodeficiency virus (HIV) is called HIV transmission. People can get or transmit HIV only through specific activities, such as sex or injection drug use. HIV can be transmitted only in certain body fluids from a person who has HIV. Bodily fluids that can transmit HIV include blood, semen (“cum”), pre-seminal fluids (“pre-cum”), rectal fluids, vaginal fluids, and breast milk.

HIV transmission is only possible if these fluids come in contact with a mucous membrane, an open cut or sore, or are directly injected into the bloodstream (from a contaminated needle or syringe). Mucous membranes are found inside the rectum, the vagina, the opening of the penis, and the mouth.

In the United States, HIV is transmitted mainly by:

• Having anal or vaginal sex with someone who has HIV without using a condom or who is not taking medicines to prevent or treat HIV.
• Sharing injection drug equipment (“works”), such as needles or syringes, with someone who has HIV.

HIV can also be transmitted from mother to child during pregnancy, childbirth (also called labor and delivery), or breastfeeding. This is called perinatal transmission of HIV. Perinatal transmission of HIV is also called mother-to-child HIV transmission.

How is HIV not transmitted?

You cannot get HIV from:

• Casual contact with a person who has HIV, such as a handshake, a hug, or a closed-mouth kiss (“social” kissing).
• Contact with objects, such as toilet seats, doorknobs, or dishes used by a person who has HIV.
• Mosquitoes, ticks, or other biting insects.
• Other sexual activities that do not involve the exchange of body fluids (for example, touching).
• Donating blood or receiving a blood transfusion.

Use the You Can Safely Share…With Someone With HIV infographic from HIVinfo to spread this message.

How can I reduce the chances of getting HIV?

Anyone can get HIV, but you can take steps to protect yourself from HIV.

• Get tested for HIV. Talk to your partner about HIV testing and get tested before you have sex. Use the GetTested locator from the Centers for Disease Control and Prevention (CDC) to find an HIV testing location near you.
• Choose safer sexual behaviors. HIV is mainly transmitted by having anal or vaginal sex without a condom or without taking medicines to prevent or treat HIV.
• Use condoms correctly every time you have sex. Read this fact sheet from CDC on condom use.
• Limit your number of sexual partners. The more partners you have, the more likely you are to have a partner with poorly controlled HIV or to have a partner with a sexually transmitted infection (STI). Both factors can increase the risk of HIV transmission.
• Get tested and treated for STIs. Ask your partners to get tested and treated, too. Having an STI can increase your risk of getting HIV or transmitting it to others.
• Talk to your health care provider about pre-exposure prophylaxis (PrEP). PrEP is an HIV prevention option if you do not have HIV but are at an increased risk of getting HIV (for example, if your partner has HIV or if you inject drugs). For more information, read the HIVinfo fact sheet on Pre-Exposure Prophylaxis (PrEP).
• Do not inject drugs. But if you do, use only sterile drug injection equipment and water, and never share your equipment with others.

If I have HIV, how can I prevent passing it to others?

Take HIV medicines as directed by your doctor. Treatment with HIV medicines (called antiretroviral therapy or ART) helps people with HIV live long, healthy lives. ART cannot cure HIV, but it can reduce the amount of HIV in the body (called the viral load). One of the main goals of ART is to reduce a person's viral load to an undetectable level.

An undetectable viral load means that the level of HIV in the blood is too low to be detected by a viral load test. People with HIV who maintain an undetectable viral load by taking ART consistently as prescribed have no risk of transmitting HIV to sexual partners.

It is important to remember that taking HIV medicines does not prevent transmission of other STIs.

In addition to maintaining an undetectable viral load, here are some other steps you can take to make sure you prevent HIV transmission to others:

• Use condoms correctly every time you have sex.
• Talk to your partner about taking PrEP.
• If you inject drugs, do not share your needles, syringes, or other drug equipment with other people.

Are HIV medicines used at other times to prevent HIV transmission?

Yes, in addition to ART and HIV PrEP, HIV medicines are also used for post-exposure prophylaxis (PEP) and to prevent perinatal transmission of HIV.

• Post-exposure prophylaxis (PEP) 
  PEP refers to taking a short course (28 days) of HIV medicines within 72 hours after a possible exposure to HIV to prevent HIV infection. PEP should be used only in emergency situations and it is not meant for regular use by people who may be exposed to HIV frequently. For more information, read the HIVinfo fact sheet on Post-Exposure Prophylaxis (PEP).   
• Prevention of perinatal transmission of HIV 
  Pregnant women with HIV take HIV medicines for their own health and to prevent perinatal transmission of HIV. After birth, babies receive HIV medicine to protect them from infection with any HIV that may have passed from mother to child during childbirth. For more information, read the HIVinfo fact sheet on Preventing Perinatal Transmission of HIV.

This fact sheet is based on information from the following sources:

From CDC:

• HIV Prevention
• Preventing HIV with PrEP
• Preventing HIV with PEP

 From the HIV Clinical Practice Guidelines at Clinicalinfo.HIV.gov:

• Recommendations for the Use of Antiretroviral Drugs During Pregnancy and Interventions to Reduce Perinatal HIV Transmission in the United States:
  • Antepartum Care for Individuals With HIV: Overview
  • Management of Infants Born to People with HIV Infection: Antiretroviral Management of Infants With In Utero, Intrapartum, or Breastfeeding Exposure to HIV

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