The Body: The Complete HIV/AIDS Resource
Follow Us Follow Us on Facebook Follow Us on Twitter Download Our App
Professionals >> Visit The Body PROThe Body en Espanol
  • Email Email
  • Comments Comments
  • Printable Single-Page Print-Friendly
  • Glossary Glossary

Basic Information on Pre-Exposure Prophylaxis (PrEP)

July 16, 2013

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.

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 a pill that contains two HIV medications every day. These are the same medicines used to stop virus growing in people who are already infected.

Why Take PrEP?

The HIV epidemic in the United States is growing. There are about 50,000 new HIV infections each year. These infections are happening more often in some groups of people and some areas of the country than in others.

Is PrEP a Vaccine?

No. PrEP medication is not injected into the body and does not work the same way as a vaccine. You will take a pill every day by mouth. The medication 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). These medicines work by blocking important pathways that the HIV virus uses to set up an infection. If you take Truvada as PrEP daily, the presence of the medication in your bloodstream can often stop the HIV virus from establishing itself and spreading in your body. If you do not take the Truvada pills every day, there may not be enough medicine in your bloodstream to block the virus.


Should I Consider Taking PrEP?

PrEP is not for everyone. Doctors prescribe PrEP for some patients who have a very high risk of coming in contact with HIV by having unprotected sex with a person who has HIV infection. You should consider PrEP if you are a man or woman who has sex sometimes without using a condom, especially if you have a sex partner who you know has HIV infection, if you don't know whether your partner has HIV infection but you know they have risks for it (for example, they inject drugs or are having sex with other people in addition to you), or if you have recently been diagnosed with a sexually transmitted infection. If your partner has HIV infection, PrEP may be an option to help protect you from getting HIV infection while you try to get pregnant, during pregnancy, or while breastfeeding.

How Well Does PrEP Work?

PrEP was tested in several large studies with men who have sex with men, men who have sex with women, and women who have sex with men. All people in these studies 1) were tested at the beginning of the trial to be sure that they did not have HIV infection, 2) agreed to take an oral PrEP tablet daily, 3) received intensive counseling on safe-sex behavior, 4) were tested regularly for sexually transmitted infections (STIs), and 5) were given a regular supply of condoms.

For several studies, we have results that showed that PrEP was effective in reducing the risk of getting HIV infection.

  • Among men who have sex with men who were given PrEP medication to take, overall they were 44% less likely to get HIV infection than those who took a pill without any PrEP medicine in it. This was an average that included men who didn't take the medicine every day and those who did. Among the men who said they took most of their daily doses, PrEP reduced the risk of HIV infection by 73% or more, up to 92% for some.
  • Among men and women in couples where their partner had HIV infection and they initially did not ("HIV discordant" couples), those who received PrEP medication were 75% less likely to become infected than those who took a pill without any medicine in it. Among those who said they took most of their daily doses, PrEP reduced the risk of HIV infection by up to 90%.
  • Among men and women who entered the studies as individuals (not as a couple), PrEP worked for both men and women in one study where those receiving the medication were 62% less likely to get HIV infection. For those who said they took most of their daily doses, PrEP reduced the risk of HIV infection by up to 85%. But in one study, only about 1 in 4 women (<26%) had PrEP medication found in their blood when it was checked and that study found no protection against HIV infection.

More information on the details of these studies.

Is PrEP Safe?

The clinical trials also provided safety information on PrEP. Some people in the trials had early side effects like an upset stomach or loss of appetite but these were mild and usually went away within the first month. Some people also had a mild headache. No serious side effects were observed. You should tell your doctor if these or other symptoms become severe or do not go away.

How Can I Start PrEP?

If you think you may be at high risk for HIV, talk to your doctor about PrEP. If you and your doctor agree that PrEP might reduce your risk of getting HIV infection, you will need to come in for a general health physical, blood tests for HIV, and tests for other infections that you can get from sex partners. Your blood will also be tested to see if your kidneys and liver are functioning well. If these tests show that PrEP medicines are likely to be safe for you to take, and that you might benefit from PrEP, your doctor may give you a prescription after discussing it with you.

Taking PrEP medicines will require you to follow-up regularly with your doctor. You will receive counseling on sexual behaviors and blood tests for HIV infection and to see if your body is reacting well to Truvada. Your doctor may also check the level of medication in your blood periodically. You should take your medicine every day as prescribed, and you will receive advice about ways to help you take it regularly so that it stands the best chance to help you avoid HIV infection. Tell your doctor if you are having trouble remembering to take your medicine or if you want to stop PrEP.

  • Email Email
  • Comments Comments
  • Printable Single-Page Print-Friendly
  • Glossary Glossary

This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
See Also
More on HIV Medications for HIV Prevention

No comments have been made.

Add Your Comment:
(Please note: Your name and comment will be public, and may even show up in
Internet search results. Be careful when providing personal information! Before
adding your comment, please read's Comment Policy.)

Your Name:

Your Location:

(ex: San Francisco, CA)

Your Comment:

Characters remaining: