Starting PrEP takes one doctor’s visit, a few tests and a daily habit, and stopping it safely is mostly about timing: keep taking it until your last possible exposure is well covered.
Below you’ll find both halves of the journey in order: what to sort out before the first pill, when protection begins, what the early weeks feel like, and how to stop or pause without leaving a gap.
Before your first pill: a starting PrEP checklist
If you’re wondering how to start PrEP, the steps are the same whether you choose daily or on-demand dosing. Work through this list with your doctor:
- HIV test. A fourth-generation test confirms you’re HIV negative. PrEP is two medicines, which isn’t enough to treat HIV and could lead to resistance.
- Kidney check. A creatinine blood test estimates how well your kidneys filter (eGFR).
- Hepatitis B test. This decides which dosing options are safe for you.
- STI screen and pregnancy test, where relevant.
- Medicine list. Mention anything you take regularly, including painkillers and supplements.
- A recent exposure? Tell the doctor about any condomless sex in the last few weeks; it changes the order of tests.
Our guide to the tests done before you start PrEP explains what each result means. Not sure PrEP is for you at all? Try the one-minute PrEP self-check.
Your first dose and when protection begins
Once your tests are clear, the doctor prescribes tenofovir disoproxil with emtricitabine (TDF/FTC), sold as Truvada or as generics such as Teno-EM. Our page on generic PrEP brands in Thailand covers the names you’ll see.
When starting daily PrEP, you take one tablet a day, at about the same time. Protection builds over the first days and weeks, and the CDC gives clear figures for when it peaks.
When protection begins
| Exposure | Daily PrEP | 2-1-1 on demand |
|---|---|---|
| Receptive anal sex | Maximum after about 7 days | 2–24 hours after the double dose |
| Receptive vaginal or front-hole sex | Maximum after about 21 days | Not suitable |
| Injecting drug use | Maximum after about 21 days | Not suitable |
The 2-1-1 option is only for cis men who have sex with men and trans women not taking estradiol, and never for anyone with hepatitis B. Our 2-1-1 dose planner shows the exact pill times. Taken as prescribed, PrEP lowers the risk of HIV from sex by about 99% and from injecting drug use by at least 74%.
What to expect in the first few weeks
Most people notice nothing at all. A minority get mild starting PrEP side effects in the first two to four weeks, often called start-up symptoms:
- nausea or an unsettled stomach;
- bloating or softer stools;
- headache or tiredness.
These usually fade as your body adjusts. Taking the tablet with food or at bedtime can help. Keep going unless your doctor tells you otherwise, and get in touch if symptoms are strong, last longer than a month, or you notice a rash or swelling.
Pick a time you can stick to, such as with breakfast or when you brush your teeth, and set a phone reminder. If you slip, our guide to what to do after a missed PrEP dose explains your next step.
How to stop taking PrEP safely
Stopping PrEP is fine when your situation changes, but the last dose matters more than the first.
People stop for many reasons: a new monogamous relationship with a partner who has an undetectable viral load or a recent negative test, a quieter period, or a move abroad. You can stop at any time, as long as you cover your last possible exposure.
Stopping by regimen
| Regimen | When to take the last pill | Before you stop |
|---|---|---|
| Daily PrEP, anal or insertive sex | Usually 2 days after the last sex | HIV test advised |
| Daily PrEP, receptive vaginal or front-hole sex | Usually 7 days after the last sex | HIV test advised |
| 2-1-1 on demand | 2 days after the last sex | Follow the full schedule |
| Daily PrEP with hepatitis B | Only with your doctor’s plan | Liver tests and follow-up |
Advice on stopping daily PrEP varies between guidelines: the figures above follow UK (BHIVA/BASHH) guidance, while some US experts suggest continuing for longer, so check with the clinic before your last pill. The CDC’s quick guide to oral PrEP for clinicians notes that protection wanes over 7–10 days once daily pills stop. An HIV test around the time you stop confirms you’re finishing on a clean slate. After stopping PrEP, you are no longer protected, so think about condoms or other prevention for any new partners.
One situation needs extra care: wanting to stop right after a risky weekend or a condom break. Don’t stop then. Keep taking your pills, because they are still working, and speak to the clinic about when your final dose should be. If you weren’t on PrEP at the time, that’s a PEP question instead.
Hepatitis B: never stop without your doctor
Tenofovir and emtricitabine also act against hepatitis B. If you have a chronic hepatitis B infection, PrEP may be keeping the virus quiet. Stopping suddenly can let it flare and damage the liver.
If your test shows hepatitis B, you’ll take daily PrEP only, and any decision to stop is made with your doctor alongside liver monitoring. This is also why on-demand dosing isn’t offered to people with hepatitis B.
If you’ve been vaccinated against hepatitis B and your test shows immunity, this doesn’t apply to you. If you’re not immune, ask your doctor whether a hepatitis B vaccine makes sense for you.
Restarting after a break
Stopping and restarting PrEP is common, and nothing about a break makes the medicine less effective later. Before restarting, you’ll usually need a fresh HIV test, especially if you had condomless sex while off PrEP. The kidney check may be repeated if it’s been a while.
For daily PrEP, the same build-up times apply again: about 7 days for anal sex and about 21 days for vaginal sex. For 2-1-1, start with the double dose if your last pill was more than a week ago.
Had sex without PrEP cover in the last 72 hours? You need PEP, not PrEP, and the sooner the better. Request urgent PEP from our clinic; you can switch to PrEP once the course ends.
Planning a trip? Read PrEP for travellers to Thailand. Ready to begin? Book your PrEP start appointment and message us first on LINE or WhatsApp so we can tell you what to bring.
Questions people ask
Can I stop PrEP anytime?
Yes, but keep taking it until your last possible exposure is covered: usually 2 days after the last sex for daily PrEP with anal sex, 7 days for receptive vaginal sex, and 2 days after the last sex for 2-1-1. Your doctor will confirm. With hepatitis B, only stop with your doctor.
How long after stopping PrEP is it effective?
Protection from daily PrEP wanes over roughly 7–10 days after the last dose, so don’t rely on it once you’ve stopped. That’s why the final doses need to cover your last exposure.
What happens if you stop taking PrEP suddenly?
You lose protection for any later exposure. If you have hepatitis B, stopping suddenly can also cause a liver flare.
Is it OK to stop PrEP for a week?
Short breaks are fine if you plan them. Cover the last exposure before the break, and rebuild protection before sex afterwards.
Do I need tests to restart PrEP?
Usually an HIV test, and sometimes a kidney check. Your doctor will decide based on how long you’ve been off it.
Written by the HIV PrEP Bangkok team, based on CDC and BHIVA/BASHH guidance. Last updated 2 October 2026.