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Did you know condoms aren’t the only way to prevent HIV? Pre-exposure prophylaxis (PrEP) is a medicine taken daily to prevent HIV infection in people who haven’t already contracted the virus.

The medicines works by blocking an enzyme, called HIV reverse transcriptase, that the virus uses to replicate within the body. If HIV enters your body, PrEP stops the virus from infecting you.

Learn more about UPMC’s HIV services

There are two different options for PrEP. They’re sold under the brand names Truvada® and Descovy®.

Descovy® hasn’t been tested on a wide range of populations. For this reason, it’s now prescribed only for men and transgender women. Truvada® is approved for people at risk of acquiring HIV from vaginal sex, anal sex, and IV drug use. Both also are used in combination with other medicines to treat HIV.

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Who Should Take PrEP?

Everyone potentially at risk of acquiring HIV should consider taking PrEP. You must have a prescription for PrEP. You can get one from your family doctor or an HIV care provider. Your doctor will confirm that you meet the requirements for taking PrEP and don’t have medical reasons not to take it. The most important thing to do before starting PrEP is to get tested for HIV. If your HIV test returns positive, then PrEP will not treat it adequately. If you start taking Truvada or Descovy when HIV positive, the virus can become resistant to it.

People at risk of getting HIV through sex

To meet the PrEP eligibility requirements, you must be HIV negative and have had anal or vaginal sex in the past 6 months. Additionally, at least one of the following should apply to you.

  • Your sexual partner is HIV positive.
  • You were recently diagnosed with chlamydia, gonorrhea, or syphilis.
  • You don’t use condoms or inconsistently use condoms.
  • You have multiple sexual partners and you don’t know their HIV

People at risk of getting HIV through IV drug use

Those who share needles or other injection equipment (such as cookers) are eligible for PrEP. In addition, the CDC recommends PrEP for people who have an HIV positive injection partner, even if the partners aren’t sharing needles or equipment.

How do you take PrEP?

The medicine needs to build up in your body until it’s at high enough levels to protect against HIV. The drug builds up more quickly in rectal tissue, compared to vaginal tissue and blood.

When starting PrEP, take it for at least 7 days before you engage in anal sex to be fully protected. You need to take it for at least 21 days before vaginal sex or IV drug use. Use barrier protection and/or avoid
sharing injection supplies during this time.

Before you stop taking PrEP, wait 4 weeks after your last sexual encounter since you may have had contact with someone with HIV.

Are there side effects with PrEP?

PrEP can cause nausea, diarrhea, headaches, and weight loss. These symptoms affect a small number of people.

About 9% of people on Truvada® experienced nausea, the most commonly reported symptom, while 2% experienced weight loss. The symptoms typically subside after the first month of use.

In addition, PrEP can lead to slightly reduced kidney function. In rare cases, it can liver damage and loss of bone density, which can put someone at a risk of bone fractures.

Doctors monitor kidney function, liver function, and bone density in people on PrEP to ensure it isn’t causing harm. If you have kidney or liver issues or osteoporosis, let your doctor know before you start PrEP.

How Much Does PrEP Cost?

In many cases, PrEP is free. It’s also available at a low out-of-pocket cost. Ready, Set, PrEP provides free PrEP to those who don’t have prescription drug coverage. Other assistance programs cover most or all co-pays and deductibles.

How Well Does PrEP Work to Prevent HIV?

Taken as directed, PrEP is about 99% effective in preventing HIV. It is less effective if you miss doses.

Effectiveness of PrEP for people at risk through sexual contact

PrEP is highly effective at preventing HIV from both anal and vaginal sex. It is about 99% effective when taken as prescribed.

One study found that when men who have sex with men took the pill an average of four times a week, the effectiveness was 96%. When taken only twice a week, the effectiveness dropped to 76%.

For women, frequently missed doses further reduces PrEP’s effectiveness because it takes longer for the drug to become concentrated in vaginal tissue.

Effectiveness of PrEP for people at risk through IV drug use

Studies that follow people who use IV drugs show a lower effectiveness of PrEP. This is largely due to challenges of taking daily medicines among this population.

The CDC estimates that for people who inject drugs, PrEP is at least 74% effective in preventing HIV. The effectiveness is likely much higher if people who use IV drugs take it daily, as directed.

Follow-up with PrEP

Your doctor will typically prescribe PrEP for 3 months at a time. It is important to have an HIV test before starting the new prescription to make sure you are still negative. If you are at risk, your doctor can also order tests for other sexually transmitted infections such as chlamydia, gonorrhea, and syphilis.

CDC. About PrEP.

CDC. PrEP Effectiveness. Pre-Exposure Prophylaxis.

NAM. What are the side effects of pre-exposure prohpylaxis?

San Francisco AIDS Foundation. PrEP: The Basics.

About Infectious Diseases

If you have a disease caused by bacteria, fungi, parasite, or virus, the UPMC Center for Care of Infectious Diseases can help. Our team of experts is specially trained in the prevention and treatment of infectious diseases, including of HIV-AIDs, postsurgical and transplant infections, illnesses caused by international travel, and more. We research infectious diseases and participate in clinical trials to learn more and develop better treatment and prevention methods. Visit our website to find an expert near you.