PrEP (pre-exposure prophylaxis) is medicine people at risk for HIV take to prevent getting HIV from sex or injection drug use. When taken as prescribed, PrEP is highly effective for preventing HIV.
This section answers some of the most common questions about PrEP.
What is PrEP?
PrEP (pre-exposure prophylaxis) is medicine people at risk for HIV take to prevent getting HIV from sex or injection drug use.
Are there different types of PrEP?
There are two medications approved for use as PrEP: Truvada® and Descovy®.
- Truvada® is for all people at risk through sex or injection drug use.
- Descovy® is for people at risk through sex, except for people assigned female at birth who are at risk of getting HIV from vaginal sex.
Is PrEP safe?
- PrEP is safe but some people experience side effects like diarrhea, nausea, headache, fatigue, and stomach pain. These side effects usually go away over time.
- Tell your health care provider about any side effects that are severe or do not go away.
- Learn more about side effects from the Truvada® and Descovy®.
How effective is PrEP?
PrEP is highly effective for preventing HIV.
- PrEP reduces the risk of getting HIV from sex by about 99% when taken as prescribed.
- Although there is less information about how effective PrEP is among people who inject drugs, we do know that PrEP reduces the risk of getting HIV by at least 74% when taken as prescribed.
- PrEP is much less effective when it is not taken as prescribed.
How long do I have to take PrEP before it is highly effective?
- PrEP reaches maximum protection from HIV for receptive anal sex (bottoming) at about 7 days of daily use.
- For receptive vaginal sex and injection drug use, PrEP reaches maximum protection at about 21 days of daily use.
- No data are available for insertive anal sex (topping) or insertive vaginal sex.
Learn more about the PrEP effectiveness estimate.
Is PrEP right for me?
PrEP may be right for you if you test negative for HIV, and any of the following apply to you:
You have had anal or vaginal sex in the past 6 months and you
- have a sexual partner with HIV (especially if the partner has an unknown or detectable viral load),
- have not consistently used a condom, or
- have been diagnosed with an STD in the past 6 months.
You inject drugs and you
- have an injection partner with HIV, or
- share needles, syringes, or other equipment to inject drugs (for example, cookers).
You have been prescribed PEP (post-exposure prophylaxis) and you
- report continued risk behavior, or
- have used multiple courses of PEP.
If you are a woman and have a partner with HIV and are considering getting pregnant, talk to your doctor about PrEP if you’re not already taking it. PrEP may be an option to help protect you and your baby from getting HIV while you try to get pregnant, during pregnancy, or while breastfeeding.
Can adolescents take PrEP?
Yes. PrEP is approved for use by adolescents without HIV who weigh at least 75 pounds (35 kg) and who are at risk for getting HIV from sex or injection drug use.
How can I start PrEP?
Talk to your health care provider if you think PrEP may be right for you. PrEP can be prescribed only by a health care provider.
- Before beginning PrEP, you must take an HIV test to make sure you don’t have HIV.
- While taking PrEP, you’ll have to visit your health care provider every 3 months for
- follow-up visits,
- HIV tests, and
- prescription refills.
- Ask your health care provider about self-testing and telehealth services for follow-up visits.
Can I start PrEP or continue taking PrEP without in-person visits to a provider?
Yes. With telemedicine (phone or video consultation with a health care provider) and mail-in self-testing, it is possible to order a specimen collection kit which contains the supplies to do all the testing required to start or continue taking PrEP, even if an in-person appointment is not possible. Contact your health care provider to see what options are available to you.
What if I need to stop taking PrEP?
There are several reasons why people stop taking PrEP:
- Your risk of getting HIV becomes low because of changes in your life.
- You don’t want to take a pill as prescribed or often forget to take your pills.
- You have side effects from the medicine that are interfering with your life.
- Blood tests show that your body is reacting to PrEP in unsafe ways.
Talk to your health care provider about other HIV prevention methods that may work better for you.
If I stopped taking PrEP, how do I start taking it again?
Tell your health care provider that you would like to start taking PrEP again. You will need to take an HIV test before you start PrEP to make sure you don’t have HIV.
Can I take PrEP just once, if I think I might have recently been exposed to HIV?
- PrEP is for people who are at ongoing risk for HIV.
- PrEP is not the right choice for people who may have been exposed to HIV in the last 72 hours.
- If you may have been exposed to HIV in the last 72 hours, talk to your health care provider, an emergency room doctor, or an urgent care provider about PEP (post-exposure prophylaxis).
Why do I need to take PrEP as prescribed?
- You must take PrEP as prescribed for it to work.
- If you do not take PrEP as prescribed, there may not be enough medicine in your bloodstream to block the virus.
- The right amount of medicine in your bloodstream can stop HIV from taking hold and spreading in your body.
Will PrEP interfere with my hormone therapy?
There are no known drug conflicts between PrEP and hormone therapy, and there is no reason why the drugs cannot be taken at the same time.
Can I stop using condoms if I take PrEP?
- PrEP provides protection from HIV, but does not protect against other STDs.
- Condoms can help prevent other STDs that can be transmitted through genital fluids, such as gonorrhea and chlamydia.
- Condoms are less effective at preventing STDs that can be transmitted through sores or cuts on the skin, like human papillomavirus, genital herpes, and syphilis.
If I am not at ongoing risk for getting HIV, can I take PrEP only when I’m at risk?
Taking PrEP only when you are at risk for getting HIV is known as “on-demand” PrEP.
- It is also known as “intermittent,” “non-daily,” “event-driven,” or “off-label” PrEP use.
- The type of “on-demand” PrEP that has been studied is the “2-1-1” schedule. This means taking 2 pills 2-24 hours before sex, 1 pill 24 hours after the first dose, and 1 pill 24 hours after the second dose.
- There is scientific evidence that the “2-1-1” schedule provides effective protection for gay and bisexual men* when having anal sex without a condom.
- We don’t know how “on-demand” PrEP works for heterosexual men and women, people who inject drugs, and transgender persons.
Some health departments in the United States and some health organizations in Europe and Canada are offering guidance for “on-demand” PrEP as an alternative to daily PrEP for gay and bisexual men at risk for HIV.
This type of use is not currently part of CDC’s guidelines for PrEP use, which still recommends daily use for those at risk for HIV. Taking PrEP once a day is currently the only FDA-approved schedule for taking PrEP to prevent HIV. When taken as prescribed, PrEP is highly effective for preventing HIV.
Anyone considering PrEP should discuss the issue with their health care provider.
* The term “gay and bisexual men” is used to describe men who identify as gay or bisexual, as well as men who have sex with men who do not identify as gay or bisexual.