What is Pre-Exposure Prophylaxis (PrEP)?
“PrEP” stands for Pre-Exposure Prophylaxis. The word “prophylaxis” means “to prevent or control the spread of an infection or disease.” PrEP is a way for people who don’t have HIV to prevent HIV infection by taking a pill every day. The pill contains two medicines that are also used to treat HIV. If you take PrEP and are exposed to HIV through sex or injection drug use, these medicines can work to keep the virus from taking hold in your body.
Along with other prevention methods like condoms, PrEP can offer good protection against HIV if taken every day.
Can anyone use PrEP?
PrEP is not for everyone. CDC recommends PrEP be considered for people who are HIV-negative and at substantial risk for HIV infection. This includes anyone who:
- Is in an ongoing relationship with an HIV-infected partner;
- Is not in a mutually monogamous relationship with a partner who recently tested HIV-negative; and is a
- gay or bisexual man who has had sex without a condom or been diagnosed with a sexually transmitted infection within the past six months;
- heterosexual man or woman who does not regularly use condoms when having sex with partners known to be at risk for HIV (e.g., injecting drug users or bisexual male partners of unknown HIV status); or
- Has, within the past six months, injected illicit drugs and shared equipment or been in a treatment program for injection drug use.
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.
PrEP is a powerful HIV prevention tool. However, for sexually active people, no prevention strategy is 100% effective. Therefore, individuals who use PrEP should use it along with other effective HIV prevention strategies. These include:
- Using condoms consistently and correctly
- Getting HIV testing with your partners
- Getting STD testing with your partners
- Choosing less risky sexual behaviors, such as oral sex.
- If you inject drugs, participating in a drug treatment program or using sterile drug injection equipment.
Also, 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 page more information.
IS PrEP a Vaccine?
No. PrEP medicine is not injected into the body and does not work the same way as a vaccine. Currently, there is no vaccination to prevent HIV infection, though researchers are seeking to develop one. Read more on our Vaccines page.
What Medications are used in PrEP?
The pill approved by the U.S. Food and Drug Administration (FDA) for daily use as PrEP for people at very high risk of getting HIV infection is called Truvada®. Truvada® is a combination of two HIV medications (tenofovir and emtricitabine). These medicines work by blocking important pathways that HIV uses to set up an infection. 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. PrEP can only be prescribed by a health care provider and must be taken as directed to work.
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.
A description of these studies can be found at CDC’s PrEP Research page.
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 within the first month. Some people also had a mild headache. No serious side effects were observed. You should tell your healthcare provider if these or other symptoms become severe or do not go away.
Guidelines on PrEP Use
In May 2014, the U.S. Public Health Service and the CDC issued clinical practice guidelines for the use of PrEP in the U.S., along with a clinical providers’ supplement.
For more information on the key points in the CDC’s HIV PrEP Guidelines, see the video below with Dr. Dr. Jonathan Mermin, Director of CDC's Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention.
Frequently Asked Questions
Since PrEP is effective, why do I need to bother with risk-reduction strategies? Can’t I just take a pill and be safe?
If PrEP is taken daily, it offers a lot of protection against HIV infection, but it is not 100% effective. Therefore, it will provide the most protection when used with—not instead of—condoms, safer sex practices, use of clean injection equipment, and other HIV prevention methods. PrEP adds another layer of protection. It’s also important to remember that taking PrEP will not prevent you from getting syphilis, gonorrhea, chlamydia, or other sexually transmitted diseases. Similarly, for those taking PrEP because of injection drug use risks, PrEP will not protect you from getting hepatitis C, skin, or heart infections.
Can I stop and start taking PrEP?
No. Some people wonder if they can take PrEP for a few days or weeks, stop for a while, and then start again. This is sometimes called “intermittent” PrEP. Available research shows PrEP’s effectiveness declines greatly if it is not taken consistently. CDC continues to recommend daily dosing of PrEP and urges people at substantial risk for HIV infection and their health care providers to continue to follow current CDC guidelines (PDF).
- CDC - PrEP Resources Page
- CDC – PrEP 101 (Basic PrEP Q&A's)
- CDC – PrEP for HIV Prevention
- CDC – Fact Sheet: Pre-Exposure Prophylaxsis (PrEP) for HIV Prevention
- CDC – PrEP: A New Tool for HIV Prevention (Fact Sheet)
- CDC – Talk to Your Doctor About PrEP
- CDC – Fact Sheet: Proven Prevention Methods
- CDC – Statement on FDA Approval of Drug for HIV Prevention
- CDC - Statement on IPERGAY Trial of PrEP for HIV Prevention among Men Who Have Sex with Men
- CDC – Statement on PrEP Findings Among Discordant Heterosexual Couples
- FDA – Consumer Update: FDA Approves First Medication to Reduce HIV Risk
- NIH – Daily Dose of HIV Drug Reduces Risk of HIV Infection
- NIH – iPrEx study results and Q&A
- HIV Prevention Trials Network
Last revised: 03/24/2015