PrEP can be taken in more than one way
The most widely used oral PrEP is tenofovir disoproxil fumarate with emtricitabine (TDF/FTC), which can be taken in two main ways.[1],[2]
- Daily: one tablet every day, suitable for many types of exposure.
- Event-driven (2-1-1): taken only around sex, suitable only for certain groups and medicines.
Daily PrEP has broader applicability. Event-driven 2-1-1 is for selected people and regimens, not every person, exposure or medicine.[1]
Why the right choice matters
Choosing a schedule that fits your risk pattern and daily life reduces gaps in protection.[1] People who have sex infrequently and can plan ahead may find 2-1-1 more convenient, while those with regular or unpredictable risk usually do better with daily PrEP.
Choosing wrongly, such as using 2-1-1 where evidence does not support it, may leave you less protected than you think.
Risk depends on the type of exposure
Risk depends on the type of exposure, other prevention and the partner's viral load.[3] The evidence supporting 2-1-1 comes from studies in men who have sex with men, which is why it applies only to that group.[2]
Why 2-1-1 applies only to some people
TDF/FTC must reach adequate levels in the exposed tissue before and after sex. The drug builds up quickly in rectal tissue, so 2-1-1 protects men who have sex with men, as shown in studies. It builds up more slowly in vaginal tissue, so 2-1-1 is not suitable for vaginal exposure.[1],[2]
TAF/FTC and long-acting injectable PrEP behave differently, and there is no evidence supporting their use in a 2-1-1 schedule.[1]
Tests before starting PrEP
Whichever schedule you use, HIV must be ruled out before starting, and kidney function and hepatitis B checked.[1],[2] Hepatitis B testing matters because PrEP medicines also act against hepatitis B. People with chronic hepatitis B should not use 2-1-1, because stopping and starting can trigger a hepatitis flare.[2]
2-1-1 is considered only for eligible adult men who have sex with men, and not for vaginal exposure.[1],[2]
How to take it correctly
Daily: take one TDF/FTC tablet at around the same time every day. This suits many exposure contexts.[1]
2-1-1 for eligible people[1],[2]:
- Take two tablets 2–24 hours before sex.
- Take one tablet 24 hours after the first dose.
- Take one more tablet 48 hours after the first dose.
If sex continues on following days, keep taking one tablet a day until 48 hours after the last sex, as agreed with your doctor.[1],[2]
Both schedules need HIV testing and follow-up about every three months, and neither prevents other STIs.[1]
How we care for you at Dr. Kris Clinic
We help you decide which schedule suits you, based on your risk pattern, frequency and daily life, in English or Thai. We run baseline HIV, kidney and hepatitis B tests and explain how to take PrEP with clear examples.
We follow up about every three months with HIV and STI testing and can change the schedule as your life changes. Every step is confidential and judgement-free.
Frequently asked questions
Can women use 2-1-1?
It is not recommended for vaginal exposure, because the drug builds up more slowly in vaginal tissue. Daily PrEP should be used.
I forgot the dose before sex. What should I do?
2-1-1 cannot protect retrospectively. If you had a risk without following the schedule, talk to a doctor about PEP within 72 hours.
On daily PrEP, how long until I'm protected?
It depends on the type of exposure, and your doctor will advise based on your risk. Vaginal exposure generally needs a longer build-up.
I have hepatitis B. Can I use PrEP?
Daily PrEP can be used under medical supervision, but not 2-1-1, and you should not stop it yourself.
Choose a PrEP schedule according to eligibility and your type of risk; no single schedule fits every exposure.[1] Daily PrEP applies more broadly, while 2-1-1 is only for eligible people using TDF/FTC.
Talk to a doctor about this
Confidential care in Surat Thani, the mainland gateway to Koh Samui, Koh Phangan and Koh Tao. Tue–Fri 17:00–20:00 · Sat–Sun 10:00–15:00 (UTC+7)
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Dr. Krida Uakridathikarn (Dr. Kris)
Board-certified family physician with certificate training in clinical sexology and sexual medicine. He works at Suratthani Hospital and provides sexual health, hormone and LGBTQ+ inclusive care at Dr. Kris Clinic. Profile and CV
References
- CDC HIV Nexus: Clinical Guidance for PrEP (current page)
- WHO: What’s the 2+1+1? Event-driven oral PrEP (2019)
- CDC nPEP Recommendations 2025. MMWR 74(RR-1)
Keep reading
Main guide: HIV & STI prevention
PrEP vs PEP: HIV Prevention Before and After Exposure
What to Do After a Possible HIV Exposure: The First 72 Hours
After Starting PEP: The 28-Day Course and Follow-Up TestingThis article is general education, not personal medical advice or a promise of results. Diagnosis and treatment require assessment by a doctor. Content reflects the cited sources as of the update date.