The once-daily pill has been shown to reduce the risk of getting HIV from sex by about 99% when taken correctly.
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The Centers for Disease Control and Prevention (CDC) has updated its guidance on pre-exposure prophylaxis (PrEP), urging doctors to talk to anyone who is sexually active about the medications that can help prevent HIV.

The CDC updated its clinical guidance on Wednesday in an effort to increase awareness and availability of the medication. PrEP is a preventative medication that lowers the risk of getting HIV from sex by up to 99% when it's taken correctly.

CDC updates its guidelines about PrEP to prevent HIV
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PrEP use has increased over the years and that, along with more testing and treatment, has lowered the number of new HIV infections, the CDC says. From 2015 to 2019, for example, new HIV infections fell 8%.

"An estimated 1.2 million persons have indications for PrEP use," the guidance reads. However, the CDC says, only about 25% of the people who could benefit from the medication were actually taking it in 2020.

"For primary care doctors who don't deal with a lot of HIV or deal with people with high-risk lifestyles, having the CDC give the green light and say that this is an expected and routine part of your care potentially gives license to providers who otherwise might not have had this conversation," Seth Glassman, MD, an infectious disease expert who focuses on HIV and an assistant clinical professor of Medicine at the University at Buffalo Jacobs School of Medicine & Biomedical Sciences, tells Health. "This is cueing providers to think about risk behaviors in people who might not immediately strike them as high risk for HIV."

"It just makes sense to expand it to everyone," Kristen D. Krause, PhD, MPH, deputy director at the Center for Health, Identity, Behavior & Prevention Studies at the Rutgers School of Public Health, tells Health. "PrEP is a big tool in the tool kit of HIV prevention."

But what is PrEP, exactly, and how does it work? Here's what you need to know.

What is PrEP?

Let's dial it back for a second and explain HIV first: Known technically as human immunodeficiency virus, HIV is a virus that can attack the body's immune system—and, if left untreated, it can lead to AIDS (acquired immunodeficiency syndrome). There's currently no cure for HIV (that means once you get it, you have it for life), but it can be managed with proper treatment and medical care.

PrEP is a preventive measure for HIV—it's a type of medication meant for those who are at risk for HIV from sex or injection drug use, and as the CDC explains, it's "highly effective" when it's taken as prescribed.

There are currently two medications approved by the Food and Drug Administration (FDA) for use as PrEP:

  • Truvada, which is designed for people who are at risk of acquiring HIV through sex or injection drug use
  • Descovy, which is for people who are at risk of acquiring HIV through sex. Note: Descovy is not for people who were assigned female at birth, who are at risk of getting HIV from vaginal sex.

How does PrEP work?

Both Truvada and Descovy "have essentially the same drugs—emtricitabine plus tenofovir," Jamie Alan, PharmD, PhD, associate professor of pharmacology and toxicology at Michigan State University, tells Health. "They differ in that they contain slightly different formulations of tenofovir," she adds.

The medications target a unique enzyme in HIV called reverse transcriptase, which then prevents the virus from replicating and infecting cells in the body, Alan explains. "The levels of the antivirals in the blood and mucosa interfere with HIV's ability to set up an infection," infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, tells Health.

Who benefits from PrEP?

It's a pretty broad group. "Everyone who is exposed to HIV benefits from PrEP," Dr. Adalja says.

The CDC says that people who meet the following criteria should consider taking PrEP:

  • Those who have had anal or vaginal sex in the last six months and have a sexual partner with HIV
  • Those who haven't consistently used a condom
  • Those who have been diagnosed with an STD in the past six months
  • People who inject drugs and have an injection partner with HIV
  • People who use injection drugs and share needles, syringes, or other equipment to inject drugs
  • People who have been prescribed post-exposure prophylaxis (PEP, medicine to prevent HIV after a possible or known exposure) and continue to engage in high-risk behavior
  • People who have taken multiple courses of PEP

It's also important to consider PrEP if you're having sex with someone and you don't know their HIV status, Alan says. "Taking this medication dramatically reduces the chance that you will be infected with HIV if you are exposed to the virus," she adds.

RELATED: What Is HIV?

Are there any risks to taking PrEP?

The CDC stresses that PrEP is safe, but notes that people can experience some side effects. Those include:

  • Diarrhea
  • Nausea
  • Headache
  • Fatigue
  • Stomach pain

However, the CDC says that those side effects usually go away over time. "These side effects should be weighed against the possibility of getting infected with the virus," Alan says.

In order to begin a PrEP regimen, the CDC says people are required to take an HIV test to make sure they don't have HIV (you cannot take PrEP if you have HIV—according to Planned Parenthood, it may make the virus even harder to treat). Once you begin PrEP, you'll have to check in with your doctor (in person, via telemedicine, or through mail-in self-testing) for follow-up visits, HIV tests, and prescription refills.

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