HIV Prevention

Pre-Exposure Prophylaxis (PrEP)

Last Reviewed: December 11, 2023

Key Points

  • Pre-exposure prophylaxis (PrEP) is HIV medicine taken to reduce the chances of getting HIV infection. PrEP is used by people who do not have HIV but are at high risk of being exposed to HIV through sex or injection drug use.
  • When taken as prescribed by your doctor, PrEP can help you stay protected against HIV if a condom breaks, is not used correctly, or is not used every time.
  • Two HIV oral medicines (pills) are approved by the U.S. Food and Drug Administration (FDA) for use as PrEP: Truvada and Descovy. To be effective, you must take oral PrEP medicines consistently each day.
  • The FDA has approved a new, long-acting injectable PrEP medicine: Apretude. It is delivered as an injection once every two months. Likewise, you must take PrEP injections at the prescribed time to be effective.
  • It is important to know that PrEP does not protect you against other sexually transmitted diseases (STDs) and should always be used with condoms.
  • The Centers for Disease Control and Prevention (CDC) reports that studies on PrEP effectiveness have shown that consistent use of PrEP reduces the risk of getting HIV from sex by about 99% and from injection drug use by at least 74%.

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, Descovy, and Apretude. Which medicine to use for PrEP depends on a person’s individual situation.

If a person is exposed to HIV through sex or injection drug use, having the PrEP medicine in the bloodstream can stop HIV from taking hold and spreading throughout the body. However, if PrEP is not taken as prescribed, there may not be enough medicine in the bloodstream to block the virus.

Should I consider taking PrEP?

PrEP is used by people who are HIV negative and 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 (CDC) recommends that you should consider PrEP if you are HIV negative, have had anal or vaginal sex in the past 6 months, and:

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 risk behavior, 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 studies on PrEP effectiveness have shown that consistent use of PrEP reduces the risk of getting HIV from sex by about 99% and from injection drug use by at least 74%.

Currently, Apretude shots are not recommended for people who inject drugs. Descovy is not for use in people assigned female at birth who are at risk of getting HIV from vaginal sex, because its effectiveness has not been studied.

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, insomnia, etc. These side effects are not serious and generally go away over time. 

If you are taking PrEP, tell your health care provider 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.

What happens once you start PrEP?

Once you start oral PrEP (Truvada or Descovy), you will need to take your PrEP pills every day. PrEP is much less effective when it is not taken every day.

Likewise, if you are taking Apretude, do not miss any injections. Missing injections increases your risk of getting infected with HIV.

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.  

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 every day 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.