01 — The short answer
Running late with a dose? Take it now.
Can I take PEP 2 hours late? Yes. If you are 2 hours late, take your dose as soon as you notice, then take the next one at your usual time.
A dose a couple of hours early or late now and then is not a reason to worry, and it does not mean your course has failed. What matters is that you keep taking one dose every day for the full 28 days. Don’t take two doses to catch up, and don’t stop the course.
If you are much later than that, missed a whole day, or were sick after a tablet, read on for each situation. If you are still unsure, call, LINE or WhatsApp us and tell us which medicine you have and when you last took it.
02 — Why it’s usually fine
A few hours late: why PEP still works.
PEP medicines stay active in your body for longer than the 24 hours between doses.
The antiretroviral medicines used for PEP build up to a steady level over the first days of the course. Because they are cleared slowly, a short delay leaves enough medicine in your system to cover the gap. That leeway is the reason a late tablet is rarely a problem.
Leeway is not the same as optional, though. The San Francisco AIDS Foundation puts it simply on its PrEP and PEP service page: PEP does not work if you do not take the medications. Our guide to what HIV PEP is and how it works explains why the full daily course matters.
03 — Scenarios
30 minutes, 3 hours or 12: what to do.
Most late doses need one simple action: take the tablet now and carry on as normal.
The table below sums up the general advice from HIV charities and medicine leaflets. Exact cut-offs depend on the medicines in your course, which the next section explains.
How late is too late? Missed dose scenarios
| How late | What to do | Next dose |
|---|---|---|
| Up to 30 minutes | Take it now, nothing else needed | Usual time |
| 1–3 hours | Take it now; no extra tablet | Usual time |
| Several hours, next dose still far off | Take it now | Usual time |
| Next dose almost due | Follow your leaflet or ask us; you may need to skip it | Usual time, never doubled |
| A whole day or more | Take one dose and contact us | As we advise |
04 — Your medicine’s rules
When the next dose is close: check your leaflet.
There is no single cut-off for every PEP regimen, so the leaflet in your box is the best guide.
PEP is usually a combination of two or three medicines, and each leaflet gives its own missed-dose rule. Two common examples show how different they can be:
- Tenofovir disoproxil with emtricitabine (Truvada): the UK leaflet says to take the missed tablet if you notice within 12 hours of your usual time; if it’s 12 hours or more, skip it and take the next one as normal.
- Dolutegravir (Tivicay): the leaflet says to take it as soon as you remember, but if the next dose is due within 4 hours, skip the missed one.
If your course combines medicines with different rules, or your tablets are a combination brand, don’t guess. Message us with a photo of the pack and we’ll tell you what to do. Every leaflet agrees on one point: never take a double dose to make up for a missed one.
05 — Being sick
Vomited after a tablet? Timing decides.
If you vomit soon after a dose, you may need another tablet; if it was well after, you usually don’t.
The Truvada leaflet, for example, says to take another tablet if you vomit less than 1 hour after taking it, and not if it’s later. HIV i-Base notes that PEP has been absorbed after about 2 hours.
Vomiting, diarrhoea and doses
| Situation | Usual advice | Contact us? |
|---|---|---|
| Vomited within 1 hour | Often another tablet; check your leaflet | Yes, if unsure |
| Vomited after 1–2 hours or more | Usually no extra tablet | Only if unsure |
| Nausea most days | Take with food; ask about anti-sickness tablets | Yes |
| Repeated vomiting or ongoing diarrhoea | Doses may not be absorbed well | Yes, the same day |
Heavy drinking makes vomiting and forgotten doses more likely, so take your tablet before a night out.
06 — A day or more
Missed a whole day? Don’t stop, get advice.
A full missed day is more serious than a late dose, but it rarely means your course is over.
If a day has passed, take a single dose now and contact us. Don’t take two to catch up. Depending on how long the gap was, when in the course it happened and which medicines you take, the doctor may simply ask you to continue.
Contact us the same day if any of these apply:
- You missed more than one dose, or two days in a row.
- You ran out, lost your tablets or left them somewhere.
- You keep missing doses because of side effects.
- You had another possible exposure during the course.
Whatever happened, finish the course as advised and keep your follow-up tests. Our page on follow-up HIV testing in Pattaya explains when they are due.
07 — Staying on track
Remembering every day: simple systems.
A reminder you can’t ignore is the easiest way to avoid a late dose in the first place.
Reminder methods compared
| Method | Works well for | Watch out for |
|---|---|---|
| Daily phone alarm | Almost everyone | Silent mode, flat battery |
| Weekly pill box | Seeing at a glance if you took it | Keep labelled packs too |
| Linking to a habit | Breakfast or brushing teeth | Routines change on holiday |
| Tick-off calendar | Counting down the 28 days | Needs to stay visible |
Want to move your dose time, say from late night to morning? You can usually shift it once, by taking the next dose a little early or late, then keep the new time. Tell us first if the change is large.
08 — Travel and help
Time zones, flights and when to call.
On a long flight, keep roughly 24 hours between doses rather than following the local clock.
Many visitors start PEP in Pattaya and finish it at home. Set an alarm on Thai time before you fly, then ease your dose time towards your new time zone. Our guide to PEP for tourists in Thailand covers flights, carrying tablets and follow-up abroad.
Still unsure after a late or missed dose? A short message is always better than worrying alone. If you haven’t started PEP yet and the exposure was recent, check how much of the 72-hour PEP window is left and see what happens at your PEP visit.
Questions
Missed PEP doses: quick answers.
Written by the HIV PEP Pattaya team, based on HIV i-Base, SFAF and medicine leaflet guidance. Last updated 29 September 2026.
Can I take PEP an hour late?
Yes. Take it as soon as you notice and keep your usual time for the next dose. Being an hour late occasionally is unlikely to affect how well PEP works.
Is PEP still effective if I miss a dose?
An occasional missed or late dose is unlikely to stop PEP working, because the medicines stay in your body for more than a day. Repeated gaps are the concern, so contact us if it happens more than once.
Should I take two PEP tablets to make up for a missed one?
No. Take a single dose, then carry on at your usual time. Doubling up adds side effects without adding protection.
I missed a PEP dose by 12 hours. What now?
It depends on your medicines, as some leaflets say to take it and others to skip it when the next dose is close. Check your leaflet or send us a photo of the pack, and don’t double the next dose.
Do I need to restart PEP after missing doses?
Usually not, but a doctor should decide. Tell us how many doses you missed and when, and we’ll advise. If you need longer-term protection afterwards, ask about moving from PEP to PrEP in Pattaya, and see our PEP questions and answers for more.
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.