Doxy-PEP in Taichung: who it is for, 72-hour limit, what it can't do
PEP for HIV is not the only option after a risky exposure. For some bacterial sexually transmitted infections there is doxy-PEP: one dose of the antibiotic doxycycline, taken after sex.
This page explains:
- who it is for, and the time limit;
- which infections it can lower the risk of, and which it cannot;
- the problem of antibiotic resistance;
- why it does not replace condoms or regular testing.
Medically reviewed by Dr. Chao-An Chen, urologist, at 昭安泌尿科診所 (Morning Urology Clinic), West District, Taichung.
In short
- Time limit: one dose, best within 24 hours of sex and no later than 72 hours.
- What it can do: lower the risk of syphilis and chlamydia.
- What it cannot do: it does not prevent HIV, HPV (the virus that causes genital warts), genital herpes or mpox. For HIV you need a different PEP.
- Gonorrhoea: Taiwan’s guidelines do not recommend doxy-PEP to prevent gonorrhoea, because resistance is high.
- Testing: it does not replace condoms or regular sexual health testing.
What doxy-PEP is, and why time matters
Doxy-PEP (doxycycline post-exposure prophylaxis) is a way to prevent some bacterial sexually transmitted infections after an exposure. Doxycycline is a broad-spectrum antibiotic of the tetracycline group.
It does not treat an infection that is already established. It aims to stop bacteria soon after they enter the body, before they multiply. This is why timing matters: the dose works best within 24 hours of sex, and it should not be taken later than 72 hours.
| Your situation | What to do |
|---|---|
| Within 72 hours of sex without a condom (best within 24 hours) | Doxy-PEP can be assessed. It lowers the risk of syphilis and chlamydia. It does not cover HIV or other viruses. |
| More than 72 hours | Doxy-PEP is no longer suitable. Come during consulting hours, and the doctor will set your testing dates from the time of the exposure. If you already have symptoms, you will be examined and treated. |
| No symptoms, ongoing risk | Regular testing every 3–6 months. It finds infections that cause no symptoms, such as syphilis with no symptoms (latent syphilis) or chlamydia, so they can be treated early. |
Who it is for
Taiwan’s 2025 guidelines on syphilis and gonorrhoea in adults cover doxy-PEP. One dose of doxycycline may be offered to prevent syphilis in men who have sex with men and in transgender women. It should be taken within 24 hours of sex, and no later than 72 hours. The guideline gives this a strong recommendation, based on high-quality evidence. The US CDC guidelines name the same groups.
People assigned female at birth are not a routine group at present. The UK BASHH guideline (2025) allows doctors to consider it, after individual assessment, for people assigned female at birth who have a higher risk of syphilis. The only trial in women, in Kenya, did not show an effect. But hair tests found the medicine in only 29% of samples, so many women may not have taken it as planned.
If you are a woman and worried about an exposure, come within 72 hours. The doctor will plan your tests and discuss whether any prevention suits you.
Gonorrhoea: doxy-PEP is not advised
Gonorrhoea is often resistant to tetracyclines, and this differs a lot between regions. Typical (median) levels are about 82% in East Asia and the Pacific, including Taiwan, about 51% in Europe and about 27% in North America. For this reason, Taiwan’s guidelines clearly do not recommend doxy-PEP to prevent gonorrhoea.
Resistance is rising fast everywhere. In North America it grew about four times in four years. In real-world use, the drop in gonorrhoea has been much smaller than expected. So do not assume you are protected against gonorrhoea because the exposure happened abroad.
Wherever the exposure happened, the evidence for doxy-PEP is clearest for syphilis and chlamydia, not gonorrhoea. If the sex took place outside Taiwan, please tell the doctor where; it is part of the assessment.
How it is taken, and safety
One dose is the whole course. The doctor explains the dose. Do not take extra doses on your own. If you have sex again soon after, follow one rule: never take more than one dose in 24 hours. If the new sex is within 24 hours of your last dose, wait until those 24 hours have passed, then take the next dose. Extra doses can cause serious stomach and liver side effects.
Possible side effects include stomach upset, ulcers of the oesophagus (the food pipe), sensitivity to sunlight, rash, headache and dizziness.
- Do not take tablets from a friend. The doctor needs to check your allergies and your liver and kidney function first.
- Doxycycline must not be combined with oral isotretinoin, an acne medicine. Tell the doctor if you take it, have taken it recently, or plan to start it.
- Doxycycline is generally not used during pregnancy or breastfeeding. Tell the doctor if you are or could be pregnant.
Disclosure about this use of the medicine
In Taiwan, doxycycline is approved for treating certain infections, including chlamydial infection and syphilis, at treatment doses. A single dose after an exposure is not the use written in the approved product information, so it is off-label use. It follows the 2025 Taiwan guidelines. Before prescribing, we explain who it suits, the time limit, what it can and cannot do, and the known side effects. You decide after the doctor explains.
Testing is still needed
Medicine does not replace condoms, including for oral sex. If you use doxy-PEP, sexual health testing every 3 months is still advised. We also suggest a PCR test every 6 months, even without symptoms. It finds gonorrhoea and chlamydia that cause no symptoms. This test is self-paid.
If there was also a possible HIV exposure, you need a separate course of anti-HIV medicines: PEP for HIV. The two can be assessed at the same visit. If the risk keeps repeating, HIV prevention before exposure (PrEP) can also be discussed at the same visit.
If you are a foreign resident or a visitor in Taiwan
Please bring your passport or resident certificate; it is needed to create the medical record. Whether or not you have National Health Insurance, costs are explained at the consultation.
We are required by law to report certain infections to the health authority. Your personal information is protected by the Communicable Disease Control Act, Article 10.
The clinic has private consulting rooms, and patients are guided through the clinic separately, so you do not have to explain why you are here in the waiting area. Nobody will judge you. Our job is the right tests, a clear explanation, and your privacy.
Before you come
Time is the key. Doxy-PEP must be taken within 72 hours, and the earlier the better. When you contact us or arrive, start with the time of the exposure and the type of contact.
Ask on LINERelated pages
Appointments and access
Consultations are conducted in Mandarin, and can also be conducted in English.
Two things are enough to start: when it happened, and what kind of contact.
昭安泌尿科診所 (Morning Urology Clinic)
No. 98, Boguan 2nd St., West District, Taichung City 403, Taiwan（403 臺中市西區博館二街98號）
Consulting hours: Monday to Saturday (closed Sunday). Online booking is open 24 hours.
This page was produced by 昭安泌尿科診所 (Morning Urology Clinic). Medical content last updated: June 2026 (same as the Traditional Chinese version). English version published: 30 October 2026. Medically reviewed by Dr. Chao-An Chen, urologist.
Sources: Taiwan CDC and the Infectious Diseases Society of Taiwan, guidelines on syphilis and gonorrhoea in adults (clinical diagnosis, treatment and prevention), first edition, 2025 / US CDC, Clinical guidelines on the use of doxycycline post-exposure prophylaxis for bacterial STI prevention, United States, 2024 (MMWR Recomm Rep 2024;73(2)) / British Association for Sexual Health and HIV (BASHH), guideline on doxycycline post-exposure prophylaxis, 2025. Medication content follows the product information approved by the Ministry of Health and Welfare.
This page provides general medical information and does not replace an individual diagnosis or treatment plan. Who it suits, the risks and the costs are decided at a consultation with a doctor.