You may have heard about medication you can take to prevent HIV called pre-exposure prophylaxis (PrEP). You take it before having sex or using injection drugs. Find out how PrEP works, how to take it, and what to expect.
What Is PrEP?
PrEP is medicine you take to lower your risk of getting HIV from sex or injection drugs. When the medication builds up in your bloodstream, it stops HIV from taking hold in your body.
You may take PrEP if you have ongoing risk of getting infected and you don’t have HIV.
Is PrEP Safe and Effective?
If you take PrEP properly, it’s 99% effective against HIV infection from sex. PrEP doesn't work as well to prevent HIV infection if you inject drugs. Experts are still gathering information, but right now it looks like PrEP lowers your risk by about 74% if you inject drugs.
PrEP works best when you take it as prescribed. Following your doctor's instructions for PrEP can help lower your HIV infection risk. PrEP is very safe and there aren't reports of serious problems in people who take it.
How Do I Take PrEP?
You can take PrEP as a daily pill, a bimonthly, or biyearly injection.
There are two pills approved for HIV prevention: emtricitabine plus tenofovir disoproxil fumarate (Truvada) and emtricitabine plus tenofovir alafenamide (Descovy). The two injections include cabotegravir (Apretude) and lenacapavir (Yeztugo) extended-release injections.
You and your doctor will decide which option is best based on your risk for HIV:
- From sex and injection drugs, Truvada may be a good option.
- From sex that isn't vaginal, Descovy may be best for you.
- From vaginal sex, choosing another option besides Descovy is best.
- From sex and you weigh at least 77 pounds, Apretude or Yeztugo may be good options.
- From injection drugs, PrEP shots aren’t recommended.
PrEP isn’t for emergency use after HIV exposure. If you were exposed to HIV in the last 72 hours, talk to your doctor, emergency room, or urgent care provider about post-exposure prophylaxis (PEP).
How Does PrEP Work?
PrEP works by blocking an enzyme HIV needs to make copies of itself, or replicate, in your body. After you start taking PrEP, it reaches a certain level in your bloodstream and in your mucous membranes that helps protect you from being infected.
How Fast Does It Work?
PrEP may start working after a few days. The medication needs time to reach a certain level in your body to get the most protection. How long it takes to work depends on certain factors.
- If you have receptive anal sex, also known as bottoming, it may take about seven days of taking a pill every day.
- If you have receptive vaginal sex or take injection drugs, it may take 21 days of daily pills.
- It’s unclear how long it takes to work if you have insertive anal sex, also known as topping, or insertive vaginal sex.
- Doctors aren’t sure how long it takes for PrEP shots to work.
- If you take PrEP on demand, which means before planned sex, you need two pills two to 24 hours before you have sex, and then one pill 24 hours later, and another 24 hours after that.
Talk to your doctor about your sexual practices so they can tell you how long it will take for you to be protected.
How Do I Start?
You can get PrEP from any health care provider who is licensed to write prescriptions. First, talk to your doctor to see what’s right for you. You’ll need an HIV test before starting PrEP.
If you already have HIV, taking PrEP medication may create resistance to the drug, which may make it less effective for treating your HIV infection.
If you want to take a PrEP pill and you can’t do an in-office visit, you may be able to do it through telehealth. Your doctor may give you an appointment over the phone or through video. You can order an HIV testing kit, then mail in the specimen. Your doctor can help you decide if it’s right for you.
When you take PrEP, your doctor will see you regularly for office visits, HIV tests, prescription refills, or shots. If you don’t have a doctor or if you want more information about HIV self-tests, visit HIV.gov.
What Are the Side Effects of PrEP?
Most people don’t have side effects from PrEP, but it’s possible you may get them. Side effects include:
- Diarrhea
- Fatigue
- Headache
- Nausea
- Skin reactions like rashes
- Stomach pain
If you have side effects, they’ll probably get better with time. If they don’t improve, talk to your doctor.
What’s on-Demand PrEP and How Does It Work?
If you don’t have an ongoing risk of becoming infected, you may consider on-demand PrEP. This is a method where you only take pills when you’re planning to have sex in the next 24 hours. Other names for on-demand PrEP include:
- Event-driven PrEP
- Intermittent PrEP
- Non-daily PrEP
- Off-label PrEP
With on-demand PrEP, you use a 2-1-1 schedule:
- Take 2 pills two to 24 hours before sex.
- Take 1 pill 24 hours after your first dose.
- Take 1 pill 24 hours after your second dose.
If you’re a gay or bisexual man and you have anal sex without a condom, the 2-1-1 schedule may protect you from HIV. If you’re a heterosexual man or woman, if you’re transgender, or if you inject drugs, it’s not clear how well on-demand PrEP works.
The FDA hasn’t approved the PrEP 2-1-1 schedule, only the daily pills. But the CDC says there is scientific evidence to support the 2-1-1 schedule to protect gay and bisexual men after unprotected anal sex. If you’re interested in on-demand PrEP, talk to your doctor. You can also find information at the CDC and health departments and organizations in the U.S., Europe, and Canada.
Show Sources
Photo Credit: Image Source/Getty Images
SOURCES:
CDC: “How can I start PrEP?” “On-Demand Prep,” “PrEP Effectiveness,” “What is PrEP?” "Preventing HIV with PrEP."
Mayo Clinic: “PrEP: How effective is it at preventing HIV?”
New York State Department of Health AIDS Institute: “HIV Pre-exposure Prophylaxis (PrEP): Individualized HIV Prevention Frequently Asked Questions.”
Planned Parenthood: “What is PrEP?”
Washington Health Institute: “What is PrEP?”
