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Basic Information on Pre-Exposure Prophylaxis (PrEP)

June 25, 2015

Truvada pills

Pre-exposure prophylaxis, or PrEP, is a prevention option for people who are at high risk of getting HIV. It's meant to be used consistently, as a pill taken every day, and to be used with other prevention options such as condoms. Find out if PrEP is right for you.

Spread the word about PrEP with our infographics.

What Is PrEP?

"PrEP" stands for Pre-Exposure Prophylaxis. The word "prophylaxis" means to prevent or control the spread of an infection or disease. The goal of PrEP is to prevent HIV infection from taking hold if you are exposed to the virus. This is done by taking one pill every day. These are some of the same medicines used to keep the virus under control in people who are already living with HIV.

Why Take PrEP?

With 50,000 new HIV infections each year in the United States, and no cure or vaccine available, prevention is key. When taken every day, PrEP can provide a high level of protection against HIV, and is even more effective when it is combined with condoms and other prevention tools.

Is PrEP a Vaccine?

No. PrEP medicine is not injected into the body and does not work the same way as a vaccine. A vaccine teaches your body to fight off infection for several years. For PrEP, you take a pill every day by mouth. The pill that was shown to be safe and to help block HIV infection is called "Truvada" (pronounced tru vá duh). Truvada is a combination of two drugs (tenofovir and emtricitabine). If you take PrEP daily, the presence of the medicine in your bloodstream can often stop HIV from taking hold and spreading in your body. If you do not take PrEP every day, there may not be enough medicine in your bloodstream to block the virus.


Should I Consider Taking PrEP?

CDC recommends that PrEP be considered for people who are HIV-negative and at substantial risk for HIV.

For sexual transmission, this includes anyone who is in an ongoing relationship with an HIV-positive partner. It also includes anyone who 1) is not in a mutually monogamous* relationship with a partner who recently tested HIV-negative, and 2) is a

For people who inject drugs, this includes those who have injected illicit drugs in the past 6 months and who have shared injection equipment or been in drug treatment for injection drug use in the past 6 months.

For heterosexual couples where one partner has HIV and the other does not, PrEP is one of several options to protect the uninfected partner during conception and pregnancy.

People who use PrEP must be able to take the drug every day and to return to their health care provider every 3 months for a repeat HIV test, prescription refills, and follow-up.

* Mutually monogamous means that you and your partner only have sex with each other and do not have sex outside the relationship.

How Well Does PrEP Work?

In several studies of PrEP, the risk of getting HIV infection was much lower -- up to 92% lower -- for those who took the medicines consistently than for those who didn't take the medicines.

See our PrEP web page for a brief description of these studies.

Is PrEP Safe?

Some people in clinical studies of PrEP had early side effects such as an upset stomach or loss of appetite, but these were mild and usually went away in the first month. Some people also had a mild headache. No serious side effects were observed. You should tell your health care provider if these or other symptoms become severe or do not go away.

How Can I Start PrEP?

If you think you may be at substantial risk for HIV (see "Should I consider taking PrEP"), talk to your health care provider about PrEP. If you and your provider agree that PrEP might reduce your risk of getting HIV, he or she will conduct a general physical and test you for HIV and other sexually transmitted diseases. Your blood will also be tested to see if your kidneys and liver are working well. If these tests show that PrEP medicines are likely to be safe for you to take, your provider may give you a prescription. If you do not have health insurance, your provider can talk to you about medication assistance programs that help pay for PrEP for some patients.

If you do take PrEP, you will need to follow up regularly with your health care provider. You will have blood tests for HIV infection and to see if your body is reacting well to Truvada. You will also receive counseling on sexual or injection drug use behaviors.

It is important to take your medicine every day as prescribed. You will receive advice about ways to help you take it regularly so that it has the best chance to help you avoid HIV infection. Tell your provider if you are having trouble remembering to take your medicine or if you want to stop PrEP.

How Do I Speak to My Doctor or Other Health Care Provider About PrEP?

Please see the brochure Talk to Your Doctor About PrEP in English and Spanish, which has some questions that you should ask your health care provider when discussing if PrEP is right for you.

How Can I Get Help to Pay for PrEP?

PrEP is covered by most insurance programs, but if you do not have insurance, your health care provider can talk to you about medication assistance programs that help pay for PrEP medicine.

If I Take PrEP, Can I Stop Using Condoms When I Have Sex?

No, you should not stop using condoms because you are taking PrEP. If PrEP is taken daily, it offers a lot of protection against HIV infection, but not 100%. Condoms also offer a lot of protection against HIV infection if they are used correctly every time you have sex, but not 100%. PrEP medicines don't give you any protection from other infections you can get during sex (like gonorrhea, chlamydia, and hepatitis), but condoms do.

So you will get the most protection from HIV and other sexually transmitted diseases if you consistently take PrEP medicine and consistently use condoms during sex.

How Long Do I Need to Take PrEP?

You should discuss this with your health care provider. There are several reasons that people stop taking PrEP. For example,

How Long Do I Have to Be Taking PrEP Before It Is Effective?

Scientists do not yet have an answer on how long it takes PrEP to become fully effective after you start taking it. Some studies suggest that if you take PrEP every day, it reaches its maximum protection in blood at 20 days, in rectal tissue at about 7 days, and in vaginal tissues at about 20 days. Talk to your health care provider about when PrEP might be effective for you.


Can I Stop and Start Taking PrEP?

No. Some people wonder if they can take PrEP for a few days or weeks, stop for awhile, and then start again. This is sometimes called "intermittent" PrEP. All available research shows PrEP's effectiveness declines greatly if it is not taken consistently, so intermittent use is NOT recommended. PrEP must be taken every day to give the best protection against HIV.

Can You Start PrEP After You Have Been Exposed to HIV?

PrEP is only for people who are at ongoing substantial risk of HIV infection. For people who need to prevent HIV after a single high-risk event of potential HIV exposure -- such as sex without a condom, needle-sharing injection drug use, or sexual assault -- there is another option called postexposure prophylaxis, or PEP. PEP must begin within 72 hours of exposure. See our PEP Q&A for more information.


Click on the images below to view and download high resolution infographics dedicated to PrEP (Pre-Exposure Prophylaxis), an HIV prevention option that works by taking one pill every day. Are you ready for PrEP? These graphics present complex information quickly and clearly and may help answer some of your questions.

PrEP Infographic

PrEP Infographic

PrEP Infographic

Click on image below to view and download a compilation of the complete series of PrEP infographics as one brochure.

PrEP Infographics Set

This article was provided by U.S. Centers for Disease Control and Prevention. You can find this article online by typing this address into your Web browser:

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