DoxyPEP – for STI prevention after exposure 

Henkilö pitää kuvassa etualalla pilleripurkkia, jossa lukee Doximycin.

Page last reviewed 24.10.2025

What is DoxyPEP and why?

The number of sexually transmitted infection (STI) cases has increased in recent years: for example, the rates of gonorrhea and syphilis have more than doubled over a few years. Chlamydia infections have slightly decreased, but chlamydia remains clearly the most common STI in Finland. A large number of STI cases have been found in men, and most of these infections in men were transmitted through sex between men.

In recent years, there has been international discussion about whether antibiotics could be used to prevent bacterial STIs. The broadspectrum antibiotic called doxycycline has been studied for postexposure prevention of chlamydia, syphilis, and gonorrhea. 

This page applies guidelines from the United States and the United Kingdom on doxyPEP — that is, using doxycycline to prevent STIs after unprotected sex. In Finland, there is no official treatment guideline for doxyPEP. 

STIs can be prevented in different ways. Condoms, lubricants, and dental dams protect from HIV and other STIs. In addition, PrEP is a good and effective medicine for preventing HIV when it is used correctly. In recent years, there has been international debate about whether antibiotics could be used for postexposure prevention of bacterial STIs. Doxycycline has been studied for postexposure prevention of chlamydia, syphilis, and gonorrhea. 

Doxycycline has been studied in men who have sex with men, and in transgender women. In other populations, the efficacy of doxyPEP for STI prevention has not been studied or demonstrated. 

How to use doxyPEP for STI prevention? 

In Finland, there is no official guideline for doxyPEP. If one does choose to use doxyPEP for chlamydia or syphilis prevention, it is important to use the drug correctly. These guidelines are based on recommendations from the United States and the United Kingdom. 

Doxycycline can be used to prevent chlamydia and syphilis after exposure. However, it is not very effective against the strain of gonorrhea found in Finland and Europe!

DoxyPEP is recommended only for men who have sex with men, who have multiple casual partners, and who have had a bacterial STI (gonorrhea, chlamydia, or syphilis) in the past year. Studies have also shown efficacy in transgender women with similar risk profiles. 

Dosage instructions 

  • 200 mg doxycycline (two 100 mg tablets at once) should be taken preferably within 24 hours, but no later than 72 hours after having unprotected sex. 
  • If you’ve had unprotected sex on several days in a row, 200 mg doxyPEP may be taken at the end of the 72-hour period. 
  • Doxycycline should not be taken in total more than 200 mg in 24 hours. 
  • Doxycycline can irritate your throat and esophagus if it doesn’t go down properly. Tablets should be swallowed with plenty of water, and you should avoid lying down immediately after taking them. 
  • Doxycycline is poorly absorbed if taken with dairy products or supplements/medications that contain calcium, magnesium, zinc, or iron, or with certain antacids. It is important to wait 1–2 hours between these substances and doxycycline. 
  • The most common side effects are gastrointestinal symptoms such as nausea, vomiting, and diarrhea. Taking doxycycline with food may reduce stomach discomfort. 
  • Doxycycline can make skin more sensitive to sunlight. Make sure to protect yourself from the sun while using it. 
  • Even when using doxyPEP, STI testing must be done regularly! Also, get tested immediately if your partner notifies you of a possible exposure to an STI. 
  • Regular STI testing is especially important for doxyPEP users because gonorrhea infections are increasing significantly, and doxyPEP is not effective against gonorrhea. 
  • If you notice any symptoms that could be related to an STI, see a doctor or get tested for STIs immediately. 
A Hand with two pills.
200 mg doxycycline (two 100 mg tablets at once)
should be taken preferably within 24 hours.

How can one get doxyPEP? 

Doxycycline is a prescription medication, so a doctor’s prescription is required. A doctor can only prescribe medicine after making a medical diagnosis and deciding whether the medicine is suitable for the patient. You should inform your doctor why and for what purpose you are requesting the drug. 

Please note that there is no official treatment guideline for doxyPEP in Finland, and not all doctors may be aware of using doxycycline for postexposure STI prevention. Each doctor will decide individually whether to prescribe doxycycline for STI prevention after exposure.

Improper use — e.g. too much or too little — or using expired medication may reduce the effectiveness of doxycycline against bacteria. It is important always to take medication according to given instructions.

Doxycycline used for preventing STIs after exposure is not reimbursed by Kela (The Social Insurance Institution of Finland). A pack of 10 tablets costs about 7–8 euros without reimbursement, and a pack of 50 tablets costs around 25 euros (prices checked in September 2025). 

You may check uptodate prices of medicines here (in Finnish)

Ordering doxycycline from online pharmacies outside the EU regulation is illegal and may expose you to risks: there is no guarantee the medicine is what it claims to be. More information on legal EU online pharmacies can be found at Fimea (Finnish Medicines Agency). 

Benefits and risks of doxyPEP 

Studies have looked at the benefits and risks of doxycycline to help create doxyPEP guidelines. Even though the results for using doxyPEP have been promising, experts in Finland and around the world have different opinions about using antibiotics to prevent STIs. There is concern about antibiotic resistance, which means bacteria become stronger and less affected by antibiotics. 

Using too much doxycycline or not following the instructions can increase antibiotic resistance and make doxycycline less effective. This also includes using expired medicine or taking too low a dose. For example, gonorrhea has already become mostly resistant to doxycycline and some other antibiotics. 

Antibiotic resistance is especially concerning because doxycycline is used to treat many diseases. Resistant bacteria could make it harder to treat infections like pneumonia. 

Doxycycline has been studied both as a preventive medicine before sex (preexposure) and as a postexposure medicine after unprotected sex. Both approaches may reduce chlamydia and syphilis infections. However, against gonorrhea, doxycycline shows very weak efficacy in Europe. 

Using doxycycline to prevent STIs is not part of the official treatment guidelines in Finland. Based on the benefits and risks, Finnish infectious disease and STI experts do not currently recommend doxyPEP for people at high risk of STIs. 

In the USA, Centers for Disease Control and Prevention (CDC) gave the first doxyPEP treatment recommendation in fall 2023. CDC recommends doxyPEP because bacterial STIs (syphilis, chlamydia, and gonorrhea) are increasing and affect gay and bisexual men, as well as transgender women, the most. 

CDC supports doxyPEP as part of sexual health counselling, which should include regular STI testing. People using doxyPEP should get tested for chlamydia, gonorrhea, and syphilis before starting the medication and every 3–6 months after. The need to continue doxyPEP should be reassessed every 3–6 months. CDC also recommends regular HIV testing for HIVnegative men who have sex with men and transgender women using doxyPEP. 

In the CDC’s study, 200 mg doxycycline given within 72 hours reduced syphilis and chlamydia infections by over 70 %, and gonorrhea infections by about 50 %. (Note: in Finland and Europe, doxycycline’s effect on gonorrhea prevention is extremely weak.) 

 
In the UK, British Association for Sexual Health and HIV (BASHH) published its doxyPEP guidance in June 2025. In the UK, the target group for doxyPEP is cisgender gay and bisexual men and transgender women, and doxyPEP is used primarily for syphilis prevention, though it also has efficacy against chlamydia. DoxyPEP is unlikely to prevent gonorrhea, as the resistance rate to doxycycline is extremely high (> 90 %). 

In the BASHH study, doxyPEP reduced chlamydia infections by 79 % and syphilis by 80 %. 
Participants reported improved quality of life and mental health, as doxyPEP reduced anxiety about STIs and gave a sense of better control over one’s sexual health. 

The doxyPEP guidance in both the USA and the UK is as follows: 200 mg doxycycline (two 100 mg tablets at once) taken within 72 hours after having unprotected sex. If you have unprotected sex on several days in a row, you can take one 200 mg dose at the end of the 72-hour period. Doxycycline should never exceed 200 mg in any 24hour period.