Prophylaxis (PrEP and PEP)

Reviewed by: HU Medical Review Board | Last reviewed: 5/31/22 | Last updated: October 2022

There are drugs available that prevent someone from contracting HIV. These drugs reduce a person’s risk of getting the virus. These drugs are commonly known as PrEP and PEP. PrEP and PEP are for people who are HIV-negative and at risk of getting the virus.1

PrEP stands for pre-exposure prophylaxis and PEP stands for post-exposure prophylaxis. Prophylaxis means something that prevents or controls the spread of an infection or disease.1

How does PrEP work?

PrEP has revolutionized HIV prevention. It is recommended for people at an increased risk of getting HIV through sex or drug use.

When used as directed, PrEP reduces the risk of getting HIV:1

  • By 99 percent from sex
  • By 74 percent from injection drug use

It is still important to use a condom when taking PrEP. Condoms protect against other sexually transmitted infections and give additional protection against HIV.
PrEP is a prescription drug that comes in pill and injectable forms, including:2-4

  • Truvada®; (emtricitabine and tenofovir), a pill taken every day
  • Descovy®; (emtricitabine and tenofovir), a pill taken every day
  • Apretude® (cabotegravir), an injection given every 2 months after the first 2 injections, which are given 1 month apart

Some PrEP drugs come in generic form too. You must have a negative HIV test before beginning PrEP. You may also need other tests to make sure PrEP is safe for you to take.

Once you begin taking PrEP, you will need to see your doctor every 3 months for:1

  • Repeat HIV tests
  • Prescription refills
  • Other medical care

How does PEP work?

PEP (post-exposure prophylaxis) is a short course of HIV medicine taken soon after a possible exposure to HIV. These pills are taken once a day for 28 days. You must start PEP within 3 days (72 hours) of exposure. Otherwise, the treatment will not work.5

PEP is not meant for people who may be exposed to HIV often. It is for emergency situations, such as:5

  • An accidental needle stick when working with an HIV-positive person in a hospital
  • After a sexual assault, especially if the attacker’s HIV status is unknown
  • When the condom broke during sex with an HIV-positive person or a person whose HIV status is unknown
  • After sharing needles and other injection drug supplies with an HIV-positive person

If you think you may have been exposed to HIV, see a doctor right away. The sooner you start PEP the better chance it has of protecting you. Starting within 24 hours is best, if possible.

Possible side effects of PrEP and PEP

Possible side effects will depend on which drug you are taking. The side effects common to all of these drugs include:2-4

  • Nausea
  • Headache
  • Stomach pain

These side effects usually go away over time. These are not all the possible side effects of PrEP and PEP drugs. Talk to your doctor about what to expect when using PrEP or PEP. You also should call your doctor if you have any changes that concern you while taking PrEP or PEP.

Things to know about PrEP and PEP

If you need a doctor to prescribe your PrEP or PEP, you can use the HIV Services Locator to find a provider near you.

Talk to your doctor if you plan to become pregnant. They can help you find options to protect you and your baby from getting HIV while you are pregnant and while breastfeeding. You should not take PrEP and PEP drugs while you are pregnant or breastfeeding.1

Before beginning PrEP or PEP, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you are taking. This includes over-the-counter drugs.

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