Post-exposure Prophylaxis (PEP) Explained
Had a condom break or think you've been exposed to HIV? If you’re not on PrEP, then you should contact a sexual health clinic as soon as possible to get post-exposure prophylaxis (PEP).
If taken in time, it can help prevent you contracting HIV and prevent HIV infection.
Here's everything you need to know about PEP, including how it works, when to take it, and where you can access it quickly.
Three key takeaways
- PEP must be started within 72 hours of potential HIV exposure. If you think you’ve been exposed, contact your sexual health clinic as soon as you can.
- PEP is most effective when you take it exactly as prescribed for the entire month. Missing doses or stopping early reduces its effectiveness.
- PEP is emergency-only, not a prevention pill. If you’re frequently at high risk of HIV exposure, consider PrEP instead.
What is PEP?
PEP, sometimes called PEPSE (post-exposure prophylaxis for HIV following sexual exposure) is the name given to the combination of drugs that can prevent the HIV infection.
PEP should be treated as an emergency measure, like a last resort if a condom breaks during sex. It cannot be used like the morning after pill and will not protect you from other STIs.
How effective is PEP?
While not 100% effective, there are very few reports of people contracting HIV when PEP is used as prescribed.
A 2017 study studied all courses of PEP at one clinic over the course of four years. Out of 1,744 individuals who had follow-up information, only 17 (1%) went on to contract HIV. Researchers put these down to PEP being started too late or not taking it as directed.
Things that can reduce the effectiveness of PEP include:
- taking it more 72 hours after a potential exposure to HIV
- not sticking with the treatment plan
- exposure to a strain of HIV that’s resistant to the drugs in PEP
When should you take PEP?
In order for PEP to be effective, it must be started within 72 hours of potential exposure, though it’s most effective if taken within 24 hours.
So, if you’ve recently had sex or shared injection equipment and think you may have been exposed to HIV, you should take PEP as soon as possible.
Your risk of exposure is likely to be higher if:
- the person you had sex with is living with HIV
- a condom or other barrier protection wasn’t used or broke
- there was any exposure to blood
How to take PEP
It’s really important that if you’re prescribed PEP that you take it exactly as instructed, for the full 28-days as required.
You should not skip a dose or fail to complete the full month as this reduces the likelihood it will work.
If you do miss a dose and remember in less than 24 hours, take the next one as soon as you remember, but do not double dose.
Importantly, if you miss more than 48 hours of PEP, let your clinician know, as they may want you to stop the rest of your treatment.
What to expect when taking PEP
Before you can take PEP, you can expect your healthcare professionals to perform an assessment to determine your risk of exposure.
After this, they’ll request a rapid HIV test before it’s prescribed. This is because PEP isn’t recommended for people who are HIV-positive.
After completing a course of PEP, it’s important to get tested for HIV to determine if the medication was effective. You should plan to be tested after finishing treatment and again three months after the initial exposure.
PEP side effects
PEP is considered to be very safe, but like all medications, there is a chance that you may experience some side effects.
Side effects from PEP are likely to be mild in the first few days and tend to go with time. Examples of these side effects include:
It’s crucial that even if you are experiencing side effects, you do not stop taking PEP. If you are experiencing side effects, especially nausea and vomiting, you should speak to your clinician about ways to reduce them.
Where can you get PEP?
PEP is available from sexual health clinics on the NHS for free. However, because it’s a powerful course of drugs and expensive to prescribe, it’ll only be given to those who meet the guidelines.
To determine if you’re eligible, you may be asked about:
- the person you had sex with and the chances that they had HIV
- what type of sex you had (vaginal, oral or anal)
- if the other person had HIV, what their viral load is
How our expert teams of clinicians can help
If you’re worried about potentially being exposed to HIV, you should look into PrEP (pre-exposure prophylaxis). With near 100% effectiveness, PrEP can help protect you against HIV when taken as prescribed.
At Chemist4U, if you’re eligible you can carry out a quick consultation and we’ll get PrEP delivered to you the next day after approval.
No need to sit around in waiting lines - we’ll help you get back your sexual freedom as soon as possible.
Frequently asked questions about PEP
Can you take PEP when pregnant or breastfeeding?
You are fine to take PEP when pregnant or breastfeeding, as there are no known effects from taking the medicine.
Can you take PEP every time you might be exposed to HIV?
No. PEP should only be used in emergency situations and should not be used in place of other HIV prevention methods, like PrEP.
Sources
- PEP. NHS Foundation Trust. [Accessed on 9 February 2026]
- Post-Exposure Prophylaxis. HIV.gov [Accessed on 9 February 2026]
- PEP (post-exposure prophylaxis for HIV). Terrene Higgins Trust. [Accessed on 9 February 2026]
