Key takeaways

  • Postexposure prophylaxis (PEP) is a combination of antiretroviral medications that is taken after a potential exposure to HIV.
  • When taken as directed, PEP can help prevent HIV transmission.
  • It’s not a substitute for other HIV prevention methods, such as pre-exposure prophylaxis (PrEP) or barrier methods like condoms.

If you think you may have been exposed to HIV, talk with a healthcare professional as soon as possible.

Postexposure prophylaxis (PEP) is taken in emergency situations when exposure to HIV may have occurred. When taken as directed, it’s effective at preventing HIV transmission. PEP may be necessary after:

  • engaging in consensual sex, especially without a condom or other barrier method or if a barrier method breaks
  • experiencing a sexual assault
  • sharing needles or other injection drug equipment
  • experiencing an occupational injury, such as a needle stick or a cut

PEP is actually a combination of different antiretroviral drugs, which work to prevent the virus from replicating effectively in the body. Many people take one of these drug combinations:

However, 2024 research suggests that a three-drug combination may be even more effective. A healthcare professional can recommend the appropriate medication regimen.

It’s important to note that PEP is for emergency use only. It’s not a substitute for other HIV prevention methods, such as:

  • using a condom or other barrier method during sex
  • having regular screenings for HIV and other sexually transmitted infections (STIs)
  • avoiding the sharing of needles or other injection drug equipment
  • taking PrEP

To be effective, PEP must be started within 72 hours of potential HIV exposure. Time is of the essence. In fact, PEP is most effective when it’s started within 24 hours of exposure.

Because of this, it’s vital to talk with a healthcare professional as soon as possible if exposure to HIV may have occurred. This can include speaking with someone at:

  • a primary care office
  • an urgent care facility
  • a sexual health clinic
  • the emergency room

PEP medications are taken as pills daily for a total of 28 days (4 weeks).

It’s important to take PEP around the same time each day so the level of antiretroviral drugs in the body remains constant during treatment.

Missing doses of PEP can make it less effective. It may be helpful to set a daily alert on a phone or tablet to remember when it’s time for another dose. When missing one dose in a 24-hour period, it can be taken as soon as someone notices.

Remember that PEP can’t reduce the risk of other STIs or infections like hepatitis C. It also can’t prevent additional HIV exposures. Because of this, someone taking PEP should continue to use condoms during sex and avoid sharing needles and other injection equipment.

Here’s what to expect both before and after taking PEP.

Before PEP

Prior to prescribing PEP, a healthcare professional will perform an assessment to determine the risk of exposure to HIV. The following situations may increase the risk of HIV transmission:

  • Body fluids that may contain HIV — such as those of someone who is HIV-positive or has an unknown HIV status — had direct contact with the bloodstream or mucus membranes.
  • An individual isn’t currently taking PrEP as directed by their doctor to prevent HIV.

A healthcare professional will also request rapid HIV testing before prescribing PEP. PEP isn’t recommended for people who are HIV-positive, and some people may not know their HIV status.

Other tests that may be ordered include:

  • screening for other STIs, such as syphilis, gonorrhea, and chlamydia
  • screening for other bloodborne infections, such as hepatitis B and hepatitis C
  • a pregnancy test
  • blood tests to check kidney and liver function

After PEP

After completing a course of PEP, it’s important to get tested for HIV. This can help determine if PEP was effective.

Your doctor can help you make a testing plan, which may include getting tested 4 to 6 weeks after exposure and again at 3 months after exposure.

People who contracted hepatitis C during a potential HIV exposure may also need additional testing.

PEP is very effective when taken as prescribed. It’s critical to take the medications exactly as a healthcare professional instructs, and it’s also essential to continue to take preventive measures.

What may limit the effectiveness of PEP?

PEP is less effective when:

  • waiting more than 72 hours to start PEP after a potential exposure
  • not adhering to the treatment plan
  • engaging in behaviors that increase the risk of HIV transmission
  • being exposed to a strain of HIV that’s resistant to the drugs in PEP

Some people who take PEP may experience side effects. These can include:

  • nausea or vomiting
  • diarrhea
  • fatigue
  • general ill feeling (malaise)
  • headache

In the event of side effects, it’s important not to stop taking PEP, as this can make it less effective. Instead, speak with a healthcare professional about ways to reduce side effects.

A complete course of PEP can cost hundreds of dollars without insurance. However, most insurance companies will cover PEP.

In some cases, an individual may not need to pay for PEP. For example, if a healthcare professional is exposed to HIV at work, their workplace insurance plan or worker’s compensation program typically pays for PEP.

In cases of sexual assault, the cost of PEP may be partially or completely covered. The Office for Victims of Crime provides more information about options in each state.

How to pay for PEP

The following resources may help someone pay for PEP:

  • Patient assistance programs: Many pharmaceutical companies have patient assistance programs that offer low cost or no-cost medications to eligible individuals. Some to check out are:
    • Gilead Advancing Access: Advancing Access is the patient assistance program from the producer of Truvada.
    • Merck: Merck has patient assistance programs for many of their drugs, including Isentress.
    • ViiV Connect: ViiV Connect is the patient assistance program from ViiV Healthcare, the maker of Tivicay.
  • Medicine Assistance Tool: The Medication Assistance Tool helps people find programs that can help them get prescriptions at low cost or no cost. Enter the relevant medications and some basic personal information to get started.
  • Medicaid: Medicaid is a joint federal and state program that helps cover healthcare costs for people with low income and few resources. Coverage and eligibility can vary by state.

Learn more about finding help if you can’t pay your medical bills.

PEP is a combination of antiretroviral drugs taken after a potential HIV exposure. It’s only used for emergency purposes and isn’t a substitute for other methods of HIV prevention.

When taken exactly as directed, PEP is very effective at reducing the risk of contracting HIV. PEP must be taken every day for a total of 28 days, ideally at the same time each day.

PEP is only effective when started within 72 hours of a potential exposure, and it’s more effective the sooner an individual seeks treatment. In the event of a potential HIV exposure, don’t hesitate to see a healthcare professional about PEP.