References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
PEP (post-exposure prophylaxis) is a 28-day course of HIV medication taken after a potential exposure to prevent infection. It’s highly effective when started within 72 hours, but the drugs used can cause side effects. Most are mild and temporary, but knowing what to expect helps you stick with the full course, which is critical for PEP to work.
If you’ve been prescribed PEP and are wondering whether the side effects are normal, or you’re considering whether to start PEP after an exposure, this guide covers what to expect.
Need an HIV test after PEP? Order a confidential home test kit
What Is PEP?
PEP is emergency HIV medication taken after a potential exposure, such as unprotected sex with someone who may be HIV-positive, a condom breaking, sexual assault, or a needlestick injury. It must be started within 72 hours (3 days) of exposure and taken for 28 days without missing doses.
PEP is not the same as PrEP (pre-exposure prophylaxis), which is taken before and during periods of potential exposure as ongoing prevention. PEP is a one-off emergency course.
In the UK, PEP is available free from sexual health clinics and A&E departments. Read more: What is PEP?
Common PEP Side Effects
The most commonly prescribed PEP regimen in the UK is a combination of tenofovir/emtricitabine (Truvada) plus raltegravir (Isentress) or dolutegravir (Tivicay). Side effects vary by drug but the most reported are:
| Side Effect | How Common | Usually Resolves | Management |
|---|---|---|---|
| Nausea | Very common (30-50%) | Within 1-2 weeks | Take with food, anti-nausea medication if needed |
| Fatigue/tiredness | Common (20-30%) | Within 1-2 weeks | Rest, adjust timing of doses |
| Headache | Common (15-25%) | Within first week | Paracetamol or ibuprofen |
| Diarrhoea | Common (15-20%) | Within 1-2 weeks | Stay hydrated, bland diet |
| Abdominal pain/bloating | Moderate (10-15%) | Within 1-2 weeks | Take with food |
| Dizziness | Less common (5-10%) | Within first week | Avoid driving if severe |
| Insomnia/vivid dreams | Less common (with dolutegravir) | After stopping PEP | Take medication in the morning instead of evening |
The first week is usually the worst. Most people find that side effects settle significantly after 7-10 days as the body adjusts to the medication.
Serious Side Effects (Rare)
Serious side effects from a 28-day PEP course are rare, but you should contact your clinic or go to A&E if you experience:
- Severe abdominal pain — could indicate pancreatitis or liver issues
- Yellowing of skin or eyes (jaundice) — possible liver reaction
- Severe skin rash — allergic reaction
- Dark urine or very pale stools — liver warning signs
- Muscle pain with dark urine — rare but could indicate rhabdomyolysis
- Signs of kidney problems — reduced urination, swelling in feet/ankles
These are uncommon, especially in a short 28-day course. PEP medications have extensive safety data from long-term HIV treatment use.
How to Manage PEP Side Effects
Nausea (the most common complaint)
- Always take PEP with food, not on an empty stomach
- Eat small, frequent meals rather than large ones
- Avoid spicy, greasy, or heavy food
- Ginger tea or ginger biscuits can help settle nausea
- Your clinic can prescribe anti-nausea medication (e.g., domperidone) if it’s severe
- Try taking your dose at bedtime so you sleep through the worst of it
Fatigue
- Rest when you can, especially in the first week
- Stay hydrated
- Avoid alcohol (which worsens fatigue and can interact with PEP)
- Light exercise can actually help with fatigue once the first few days have passed
Diarrhoea
- Stay well hydrated (water, diluted juice, oral rehydration sachets)
- Avoid caffeine and dairy temporarily
- Over-the-counter loperamide (Imodium) can be used if needed
Why You Must Complete the Full 28 Days
PEP only works if you complete all 28 days. The drugs need to maintain consistent levels in your body throughout the period when HIV might be establishing itself. Stopping early, even if you feel fine, can mean the medication fails to prevent infection.
Side effects are the number one reason people stop PEP early. If side effects are making it hard to continue, contact your clinic rather than stopping. They can:
- Switch you to a different drug combination with fewer side effects
- Prescribe anti-nausea or anti-diarrhoea medication
- Adjust the timing of your doses
Do not stop PEP without speaking to a healthcare provider first.
Testing After PEP
After completing PEP, you’ll need follow-up HIV testing to confirm the medication worked:
- HIV test at 4 weeks after completing PEP (8 weeks after exposure)
- Confirmatory HIV test at 12 weeks after exposure (90 days)
- Additional STI screening may be recommended, as PEP only protects against HIV, not other STIs
Order a home HIV test for your follow-up or attend your clinic for a blood test.
Read more: What is PrEP? | What is HIV? | Starting HIV treatment
Frequently Asked Questions
How sick will PEP make me?
Most people experience mild to moderate nausea and fatigue for the first 1-2 weeks. It’s uncomfortable but manageable. A minority feel significantly unwell. Very few people have to stop because of side effects. Modern PEP regimens are much better tolerated than older ones.
Can I drink alcohol while on PEP?
Small amounts of alcohol are unlikely to interfere with PEP’s effectiveness, but alcohol can worsen nausea, fatigue, and dehydration. Most clinicians recommend avoiding or minimising alcohol during the 28-day course.
Does PEP affect the contraceptive pill?
Standard PEP regimens (tenofovir/emtricitabine + raltegravir or dolutegravir) do not interact with hormonal contraception. However, if your PEP includes ritonavir-boosted drugs, these can reduce the effectiveness of the pill. Check with your prescriber.
Can I take PEP if I’m pregnant?
Yes. PEP can be given during pregnancy if the risk of HIV exposure justifies it. The drugs used have safety data in pregnancy. Your doctor will choose the most appropriate combination.
How effective is PEP?
When started within 72 hours and taken correctly for 28 days, PEP reduces the risk of HIV infection by approximately 80%. It’s not 100% effective, which is why follow-up testing is important. The sooner PEP is started after exposure, the more effective it is.
Related reading
- Are HIV Tests Accurate If You're on PrEP, PEP or ART?
- Choosing the Right PrEP Drug: Truvada vs Descovy
- Post-Exposure Prophylaxis (PEP) for HIV
- Pre-Exposure Prophylaxis (PrEP) for HIV
- PrEP and Sexually Transmitted Infections
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
