Starting PEP usually brings a wave of relief. Then, a day or two in, a new worry arrives: is this nausea normal? Should I be this tired? Is the medicine harming me? The short answer is that most people feel fine or only mildly off, and the uncomfortable bits tend to fade within the first week. This guide breaks down what to expect over the 28 days, and how to tell the difference between normal and worth a call.
Key points
- Modern PEP is much better tolerated than older regimens.
- Nausea, headache, tiredness, loose stools and vivid dreams are the most common side effects.
- Most side effects peak in the first few days and settle by the end of week one or two.
- Rash, yellow skin or eyes, or severe abdominal pain need a doctor straight away.
- Do not stop PEP on your own. Message the clinic first.
Why side effects happen at all
PEP is usually a combination of three HIV medicines. In Thailand, a common regimen includes tenofovir, emtricitabine or lamivudine, and dolutegravir. Your body is adjusting to new medicines, and the gut is usually the first place you notice it. For most people, the body adapts quickly.
Days 1 to 3: the adjustment phase
This is when side effects, if you get any, are most likely to show up.
- Nausea. Often mild, sometimes worse on an empty stomach. Taking your dose with food usually helps.
- Headache. Usually mild and responds to paracetamol.
- Tiredness. Partly the medicine, partly the stress and sleep loss that often come with needing PEP in the first place.
- Strange dreams or trouble sleeping. Dolutegravir can affect sleep in some people. Taking it in the morning can help; ask the doctor first.
Days 4 to 7: settling down
For most people, this is when things start to calm down. Nausea becomes occasional, energy returns, and the daily dose becomes routine. If side effects are getting worse rather than better at this point, it is worth checking in with the clinic.
| Side effect | How common | What usually helps |
|---|---|---|
| Nausea | Common in week one | Take with food, eat small meals |
| Headache | Common early on | Paracetamol, water, rest |
| Tiredness | Common | Sleep, avoid heavy drinking |
| Loose stools | Fairly common | Fluids, simple food |
| Sleep changes | Some people | Ask about taking it in the morning |
| Rash | Uncommon | Contact the clinic promptly |
Weeks 2 to 4: the long middle
By the second week, most people barely notice they are on PEP. The main challenge now is not side effects but remembering. Missed doses are the biggest reason PEP fails. A few habits that work:
- Take it at the same time each day, linked to something you already do, like breakfast.
- Set an alarm that repeats daily.
- Keep one spare dose in your bag.
- If you are travelling between islands or flying home, keep the tablets in your hand luggage.
Side effects worrying you?Message the clinic any time. A doctor can tell you what is normal and what to do.
The interactions people do not know about
One of the most common PEP medicines, dolutegravir, is affected by products that contain calcium, iron, magnesium, zinc or aluminium. That includes many antacids, indigestion remedies and multivitamins. They can reduce how much of the medicine your body absorbs.
The usual advice is to take PEP at least 2 hours before, or 6 hours after, these products. Tell the doctor about every supplement and remedy you use, including anything bought from a local pharmacy.
When it is not normal: call the clinic straight away
Contact a doctor promptly if you notice:
- A widespread rash, especially with fever, blistering or mouth sores
- Yellowing of the skin or the whites of the eyes
- Severe or persistent abdominal pain or vomiting that stops you keeping tablets down
- Signs of an allergic reaction such as swelling of the face or difficulty breathing (call 1669)
Also tell the doctor if you develop a fever, sore throat, swollen glands or a rash a few weeks in. These can be flu-like symptoms of early HIV, which is rare on PEP but important to check.
What if I vomit after a dose?
If you vomit within about an hour of taking a dose, the medicine may not have been absorbed, and the doctor may advise taking another. If it is later than that, you usually do not need to repeat it. Message the clinic if you are unsure, or if vomiting continues.
Should I stop PEP if I feel unwell?
Do not stop on your own. Stopping early can leave you unprotected. If side effects are hard to manage, the doctor can suggest ways to ease them, or in some cases switch one of the medicines. Most people who feel rough in the first few days are glad they kept going.
After day 28
Once the course ends, any lingering side effects usually disappear within a few days. Then come the follow-up HIV tests at about 6 weeks and 3 months after the exposure. If you are likely to need PEP again, ask about PrEP, which uses fewer medicines and is generally even easier to tolerate.
Close to finishing PEP?Ask about follow-up tests and whether PrEP makes sense for you next.
Frequently asked questions
Can I drink alcohol while on PEP?
Alcohol does not stop PEP working, but it can make nausea worse and make missed doses more likely. Keep it moderate.
Will PEP affect my contraceptive pill?
The common PEP regimens used in Thailand do not usually affect hormonal contraception, but always tell the doctor what you use so they can check.
Is it normal to feel anxious on PEP?
Yes, very. Much of what people feel during PEP is worry rather than side effects. Talking to the doctor and knowing your test dates helps.
Do side effects mean I have HIV?
No. Side effects come from the medicines. Only the follow-up tests can confirm your status.