01 — The short answer
Most people cope well: mild, early and temporary.
PEP side effects are usually mild, tend to appear in the first few days, and often ease within the first week or two as your body adjusts.
The most common complaints are an unsettled stomach, loose stools, a headache or feeling more tired than usual. Many people notice very little at all. According to the US CDC, side effects such as nausea can almost always be treated and are not life-threatening.
The one thing that matters most is to keep going. PEP only protects you if you take it every day for the full 28 days, so if something bothers you, get advice rather than skipping tablets. Our guide to how HIV PEP works explains why the whole course counts.
02 — Common effects
What you might feel, and what helps.
Modern PEP regimens are far easier to take than older ones, and most everyday symptoms respond to simple changes.
Today’s combinations usually pair tenofovir and emtricitabine with an integrase inhibitor such as dolutegravir or bictegravir.
Common PEP side effects and how to manage them
| Effect | What it feels like | What usually helps |
|---|---|---|
| Nausea | Queasy, off your food | Take the tablet with a snack or at bedtime; ginger or peppermint tea |
| Diarrhoea | Loose stools, gurgling stomach | Plenty of water, bland food, oral rehydration salts in the heat |
| Headache | Dull ache, often in week one | Rest, fluids, regular meals; ask us before taking painkillers |
| Tiredness | Heavy, low energy | Early nights, light exercise, less alcohol |
| Bloating or wind | Full, uncomfortable stomach | Smaller meals, fewer fizzy drinks |
In Pattaya’s heat, diarrhoea can dehydrate you faster than you expect, so keep a bottle of water with you. If you are being sick after doses, our page on vomiting and missed PEP doses explains when you need another tablet.
03 — The timeline
How long they last, week by week.
For most people, the first week is the hardest and things improve from there.
People often ask how long PEP side effects last, and whether they go away on their own. HIV i-Base, a UK treatment charity, says that when mild side effects happen they usually get easier after the first week or two.
Side effects over the 28 days
| When | What’s typical | What to do |
|---|---|---|
| Days 1–3 | Nausea, headache, loose stools may start | Take with food, drink water, keep your dose time |
| Days 4–14 | Symptoms settle for most people | Tell us if they are getting worse, not better |
| Days 15–28 | Usually little or nothing; some mild tiredness | Finish the course and book follow-up tests |
| After finishing | Side effects fade within days | Report any new fever or rash |
A short symptom diary, with dates and dose times, helps the doctor spot a pattern quickly.
04 — Sleep and mood
Dreams, sleep and mood: less common, still worth knowing.
Some regimens list sleep changes, dizziness and low mood among their common side effects.
The UK patient leaflet for Biktarvy, a bictegravir-based combination, lists abnormal dreams, headache, dizziness, diarrhoea, nausea, tiredness and depression as common, which it defines as affecting up to 1 in 10 people. That list is what most answers about Biktarvy PEP side effects draw on. You can check the full list in the Biktarvy patient leaflet on the UK medicines database.
Your course may use different medicines, so ask us what yours contains and read the leaflet in the box. If dreams disturb your sleep, ask about a morning dose. Low mood or dark thoughts are always worth mentioning the same day.
05 — Interactions
Antacids and supplements: space them out.
Some everyday products can stop PEP being absorbed properly, which matters more than most side effects.
Minerals such as magnesium, aluminium, calcium, iron and zinc bind to integrase inhibitors in the gut. i-Base advises leaving at least 6 hours between PEP and supplements containing magnesium, zinc or calcium, while individual leaflets give their own rules.
Medicines and supplements to space out
| Product | Why it matters | What to do |
|---|---|---|
| Antacids and indigestion remedies | Often contain magnesium or aluminium | Take PEP well before them; check your leaflet |
| Multivitamins and minerals | Iron, zinc, calcium, magnesium | Pause them or leave a long gap |
| Sports drinks and protein powders | Some have added minerals | Read the label |
| St John’s wort | Interacts with some PEP medicines | Don’t take it during PEP |
Tell the doctor about everything else you take, including prescription medicines and recreational drugs.
06 — Knowing when to act
Normal, or time to call? A simple guide.
Mild symptoms can wait for a message; a few rare reactions need urgent care.
What’s normal vs when to call
| Symptom | What it may mean | What to do |
|---|---|---|
| Mild nausea, headache, tiredness | Expected early side effect | Carry on and use the tips above |
| Symptoms still strong after 2 weeks | Poor fit with the regimen | Message us during opening hours |
| Repeated vomiting or diarrhoea | Doses may not be absorbed | Contact us the same day |
| Any rash, yellow skin or eyes, dark urine | Possible allergy or liver problem | Contact us the same day |
| Blistering rash, mouth sores, swollen face or throat, trouble breathing | Rare serious reaction | Go to a hospital emergency department now |
i-Base notes that any rash more than very mild should be shown to a doctor in case it is a rare allergic reaction. Our clinic has set opening hours, so for severe symptoms at night go straight to a hospital emergency department.
07 — Side effect or HIV?
Symptoms on PEP are not a sign of HIV.
A fever or sore throat during the course is far more likely to be a side effect, a cold or stress than HIV.
i-Base explains that HIV symptoms come from a high viral load, which PEP would prevent. Seroconversion illness, when it happens, usually starts around 10 to 14 days after exposure and feels like a heavy flu. If you feel flu-like with a rash or swollen glands in the weeks after finishing, don’t guess: contact us and get tested.
Either way, follow-up HIV testing in Pattaya gives you the real answer. PEP only covers HIV, so also consider a full STI test in Pattaya after a possible exposure.
08 — Finishing well
Don’t stop early: talk to us first.
If side effects are hard to live with, the answer is usually a change of plan, not stopping.
A doctor can suggest anti-sickness medicine, a new dose time or, sometimes, a different combination. If you have hepatitis B, stopping some PEP medicines suddenly can cause a flare, which is one more reason to get advice first. Australian guidance from ASHM lists a kidney function check at the start and at week 6 as part of routine PEP care.
The good news: i-Base states that PEP does not have long-term side effects, and the medicines leave your body soon after the last dose. Flying home mid-course? See PEP for tourists in Thailand. If you keep needing PEP, ask us about PrEP in Pattaya instead.
Worried about a symptom or a missed dose? Call, LINE or WhatsApp us during opening hours and tell us which medicines you’re taking.
Questions
PEP side effects: quick answers.
For more on timing, alcohol and sex during the course, see our PEP questions and answers.
Written by the HIV PEP Pattaya team, based on HIV i-Base and ASHM guidance. Last updated 29 September 2026.
How long do PEP side effects last?
For most people they are strongest in the first few days and ease within one to two weeks.
Do PEP side effects go away on their own?
Usually, yes, as your body gets used to the medicines. If a symptom is getting worse rather than better, or stops you taking your tablets, contact us for advice.
Does having no side effects mean PEP isn’t working?
No. Many people feel completely normal on PEP. How you feel doesn’t tell you whether it worked; only your follow-up HIV tests can.
Can side effects start in the second or third week?
It’s less common, but it can happen. A new rash, yellowing of the skin or eyes, or a fever later in the course should be checked the same day.
Does PEP make you tired?
It can, especially early on. Regular sleep, meals and water help.
Pattaya, Thailand
Don’t wait until tomorrow.
Worried about a recent exposure? Talk to us now. It’s confidential, and the sooner you start, the better PEP works.