PEP (Post-Exposure Prophylaxis)

Updated on:
February 16, 2022

Post-exposure prophylaxis (PEP) is a short course of antiretroviral drugs taken soon after possible exposure to HIV. These medications work by preventing seroconversion, which is when somebody who is HIV negative becomes HIV positive.

Here’s what you need to know about PEP, including timing, efficacy, and where to get it.


PEP is used for people who have a possible exposure to HIV. This medication is only meant to be used in emergency situations, after an event where HIV could have been transmitted.

On the other hand, pre-exposure prophylaxis (PrEP) is meant for people who may be exposed to HIV frequently. This is a once-a-day pill that is effective in preventing HIV. PrEP works by preventing the virus from establishing infection inside of the body.

It’s important to note that both PEP and PrEP are part of combination prevention. These medications can be used, along with other strategies such as condom use, sexual health education, and needle distribution programs, to minimize the risk of contracting HIV.

How soon do I need to get on PEP after a potential HIV exposure? 

Time is of the essence. When it comes to PEP efficacy, every minute counts! If you think you may have been exposed to HIV, you need to start the PEP regimen immediately. 

For PEP to work, it must be taken within 72 hours after possible exposure to the virus.

Be aware that PEP should only be used in the event of an emergency. It should not be used regularly by those who are at risk of frequent HIV exposure.

How effective is PEP?

When taken correctly and within the 72-hour timeframe, PEP is effective. However, this medication is not 100% effective. The sooner you start PEP after a possible exposure to HIV, the better.

PEP must be taken every day for 28 days. During the course, your health care provider will conduct HIV testing along with other tests.

While taking PEP, continue to use other HIV prevention methods. Condoms are an effective way of keeping you and your partner safe. It’s also important to use new, sterile needles when injecting drugs.

Are there any side effects for PEP?

PEP is very safe, though some users have reported side effects, including nausea. Some have also reported other digestive issues, including:

  • Diarrhea
  • Flatulence
  • Bloating
  • Abdominal cramps

Side effects are usually mild and can be treated with over-the-counter medications. If you experience any side effect that causes extreme discomfort or doesn’t go away, contact your healthcare provider.

Where do I get PEP?

PEP is available at emergency rooms, sexual health clinics, and some doctors’ offices. If exposure happens after hours, it’s best to visit the emergency room so that you can start taking PEP as soon as possible.

When visiting the ER or a health clinic, you will be asked about your potential exposure. From there the doctor will decide if PEP is the best course of action. You will be given a blood test for HIV, along with tests for Hepatitis B and STIs.

If you believe you've been exposed to HIV, call one of our clinicians today. We'll discuss your situation and help you to determine if PEP is right for you. At Freddie, we offer a dedicated Care Coordinator that will answer any questions or concerns you may have.

Reviewed by:
Thomas Trombetta

Thomas is passionate about gender and sexuality liberation social movements. Before beginning his work with Freddie, Thomas studied Sociology and Global & Development Studies at the University of Alberta, after which he began working with marginalized communities. In previous roles, Thomas was involved in queer and trans health education, PrEP health promotion, community-based research, HIV education, and LGBTQ2S+ advocacy.