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How Effective is PrEP?

Vicky Davis

Medically reviewed by Vicky Davis, FNP

Written by Our Editorial Team

Last updated 8/8/2021

Preventative health care is an important part of staying healthy. 

From eating nutritiously to working out and making sure you have regular check-ins with a healthcare professional, there are plenty of things you can do to ward off illness and make sure you’re in tip-top shape. 

Another preventative measure you may want to consider is taking PrEP. 

According to the Centers for Disease Control and Prevention, as of 2018, an estimated 1.2 million Americans are living with HIV. 

PrEP, also known as pre-exposure prophylaxis, is one of the many prevention strategies surrounding HIV infection — and the good news is that this prevention option is effective at what it sets out to do.

But for PrEP to be effective, it must be taken correctly. Here’s what you need to know about PrEP and its effectiveness. 

Understanding HIV

In the 1980s, cases of HIV/AIDS started rapidly spreading in the United States—particularly among the LGBTQ+ community. This led to a common misconception that it was a disease that only infected that specific community. 

The truth, however, is that anyone can become infected with HIV. 

HIV (human immunodeficiency virus) attacks the immune system. If left untreated, it can lead to AIDS (acquired immunodeficiency syndrome). There is no cure for either HIV or AIDS.

With medical care and effective treatment, however,  people with HIV can live long, healthy lives.

The only way to find out if you have been infected with HIV is through oral fluid, urine, or blood tests.

People at the highest risk for contracting HIV are:

  • Homosexual and bisexual men who have sex with men

  • Men and women who consistently do not use condoms

  • Men and women who have a sexual partner who’s HIV-positive

  • People who frequently contract STDs

  • People with multiple sex partners

  • IV drug users

If you fall into one of these categories, you may be a good candidate for PrEP as a preventative measure against contracting HIV. 

How Does PrEP Work?

PrEP lowers your risk of contracting HIV by getting and keeping an undetectable viral load. You must take the drug consistently on a daily basis. 

By doing so, you maintain levels of the medication in your bloodstream and it blocks HIV from taking hold and spreading throughout your body, thereby preventing a viral load from building up.

Truvada® and Descovy® are the brand names for PrEP treatments

The first is a combo of two drugs called tenofovir disoproxil fumarate and emtricitabine. Both are antiretroviral drugs originally approved to treat HIV.

Descovy works in a similar way, but it incorporates a newer form of tenofovir called tenofovir alafenamide. 

There is some evidence that Descovy may be slightly more effective at HIV suppression and poses less risk of adversal renal and bone events. 

One thing to know: Descovy is not approved for people at risk of contracting HIV through receptive vaginal intercourse.

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How Effective is PrEP?

Very. PrEP reduces the risk of getting HIV from sex by 99 percent. There’s not quite as much info on how effective PrEP is for IV drug users, but it is known that, overall, PrEP reduces the risk of getting HIV by 74 percent.

The two versions of PrEP, Truvada and Decovy, are both very effective when taken as prescribed.

Missing a dose or taking it late can greatly affect PrEP’s ability to prevent HIV. 

How Long Before PrEP Works?

An important thing to know: PrEP is not effective immediately. You have to be on it for a bit before it starts to do its thing. Here is when PrEP becomes effective:

  • The medication reaches maximum effectiveness from HIV for receptive anal sex at seven days of daily use. 

  • PrEP reaches maximum protection at 21 days of daily use in people who take part in IV drug use and receptive vaginal sex. 

  • No data is available for insertive vaginal or anal sex. 

Interested in Taking PrEP? 

In 49 states, PrEP requires a prescription from healthcare providers. However, in California, you can visit a pharmacy without a prescription for 30- and 60-day supplies.

If you are interested in taking PrEP, speak with healthcare providers. They may ask you about your sexual practices and relationship to recreational drugs to determine if you are a good candidate for the medication. 

You will also likely need to take an HIV test to ensure you are negative. While on PrEP, you’ll want to also get tested regularly. 

Most practitioners ask PrEP users to come back every three months for testing and to make sure you are handling the medication well.

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Taking PrEP to Prevent HIV

PrEP, or pre-exposure prophylaxis, is a medication that is one of the prevention options for those at high-risk for HIV. It’s designed to lower your risk of infection for HIV. If you are high-risk for possible infection, you may be a good candidate for the drug. 

Truvada and Descovy are the two types of PrEP that a healthcare provider may prescribe. Taking daily PrEP is incredibly effective at preventing HIV. 

If you think you are a good candidate for or have any questions about PrEP medication, contact a healthcare professional to discuss it with them. 

12 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

  1. HIV: Basic Statistics. Centers for Disease Control and Prevention. Retrieved from
  2. A Timeline of HIV and AIDS. Retrieved from
  3. About HIV. Centers for Disease Control and Prevention. Retrieved from
  4. HIV Testing. Centers for Disease Control and Prevention. Retrieved from
  5. Who is at risk of HIV/AIDS? Eunice Kennedy Shriver National Institute of Child Health and Human Development. Retrieved from
  6. PrEP (Pre-exposure prophylaxis). Centers for Disease Control and Prevention. Retrieved from
  7. Truvada Medication Information Sheet. Centers for Disease Control and Prevention. Retrieved from
  8. Hill, A., Hughes, S., Gotham, H., Pozniak, A., (2018, April). Tenofovir alafenamide versus tenofovir disoproxil fumarate: is there a true difference in efficacy and safety? Journal of Virus Eradication. Retrieved from
  9. U.S. Food & Drug Administration. FDA approves second drug to prevent HIV infection as part of ongoing efforts to end the HIV epidemic. Retrieved from
  10. PrEP Effectiveness. Centers for Disease Control and Prevention. Retrieved from
  11. Senate Bill No. 159. California Legislative Information. Retrieved from
  12. PrEP Your High-Risk Patients to Help Protect Them From HIV. American Academy of Family Physicians. Retrieved from

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.