Doxy-PEP for syphilis prevention: What is it, does it work and how can we overcome barriers to access?


For years, gay, bisexual, trans, Two-Spirit and queer (GBT2Q) communities have been experiencing unacceptably high rates of syphilis with limited action taken by others outside the work of community-based sexual health organizations. However, provincial and federal responses have been stoked due to an increase in heterosexual transmission and a rise in cases of babies born with syphilis, also known as congenital syphilis. When acquired by a fetus during pregnancy, syphilis can result in miscarriage, stillbirth or permanent disability of the newborn. Consequently, efforts to leverage innovative syphilis interventions have accelerated, alongside interest in new prevention options for GBT2Q men. One promising development is doxy-PEP, but many people are still uninformed about this intervention, including who could benefit from it and how to access it.  

What is doxy-PEP?

Doxy is short for doxycycline, which is an antibiotic used to treat bacterial infections, including bacterial sexually transmitted infections (STIs) like syphilis and chlamydia. Doxycycline is also used to prevent infections like malaria.

PEP stands for post-exposure prophylaxis, which refers to medication used to prevent an infection after a possible exposure, like how HIV PEP is used to prevent HIV.

Doxy-PEP is a medication containing doxycycline, which is taken after sex to prevent syphilis, chlamydia and some other STIs. It requires a prescription from a healthcare provider and would generally be prescribed in advance. It must be taken within three days (72 hours) of a potential exposure but ideally as soon as possible. An individual takes a dose of two 100 mg pills, no more than one time per day. Only one dose is needed for every day of condomless sex. A helpful way to remember this is the 3-2-1 rule.

Does doxy-PEP work?

Multiple studies of doxy-PEP have demonstrated that it is effective at reducing syphilis and chlamydia among trans women and gay, bisexual and other men who have sex with men (gbMSM).

Similar to how daily HIV PrEP is used to prevent HIV, doxycycline can also be taken daily as pre-exposure prophylaxis (doxy-PrEP) to prevent syphilis. There is less evidence available for doxy-PrEP and we are looking forward to data on the effectiveness of doxy-PrEP among cis and trans gbMSM and trans women to emerge from the DISCO study, currently underway in Canada.

Unfortunately, research evidence is limited concerning doxy-PEP’s effectiveness for cis women, trans men and gender-diverse people. One study of doxy-PEP among cis women in Kenya did not demonstrate effectiveness, but this was possibly because of low adherence among study participants. However, given the historic disparities in HIV and STI research, the growing impacts of increased heterosexual syphilis transmission in Canada and the alarming rise in congenital syphilis, we cannot simply take this at face value. We are in dire need of high-quality research studies on the effectiveness of doxy-PEP for STI prevention among cis women, trans men and gender-diverse people.

Should we be concerned about treatment resistance?

Despite doxycycline having been used for years to treat and prevent infections, some have raised concerns about antimicrobial resistance (AMR) in response to doxy-PEP use. AMR occurs when bacteria gain the ability to resist antimicrobial medicines, rendering them ineffective. While this must be carefully considered, no evidence of AMR has emerged through decades of antibiotic use in the treatment of syphilis and chlamydia. AMR has been observed with many antimicrobial medicines, including doxycycline use for gonorrhea, however doxycycline is not a common gonorrhea treatment in Canada.

What are barriers to doxy-PEP access and how can we address them?

Despite being new to many in the community-based sexual health sector, doxy-PEP is already being used in Canada. The 2022 edition of CBRC’s Sex Now Survey, Canada’s longest-running health survey of gay, bi, queer, and trans men, and Two-Spirit and non-binary people, demonstrated that 25% of respondents were already aware of doxy-PEP, 36% were interested in taking it and 6% had already used it.

As in the early days of HIV PrEP, queer and trans communities are demonstrating leadership addressing syphilis and other STIs by educating themselves about doxy-PEP and taking action to improve their health and well-being. However, many community members are facing barriers to accessing doxy-PEP, including a lack of provider knowledge and an unwillingness to prescribe, which also recalls the early days of HIV PrEP. This deprives community members of an effective health intervention at a time when it could do so much good.

We cannot repeat the mistakes from Canada’s HIV PrEP rollout. We urgently need national doxy-PEP guidelines to provide guidance for service providers working with communities affected by syphilis. We need increased and ongoing investment in doxy-PEP education, as well as capacity-building for service providers and affected communities. This must include intentional and meaningful investments in communities who were too often left behind in HIV PrEP efforts, including Indigenous, Black, and racialized queer and trans people, as well as queer and trans people who use drugs. Finally, we must avoid burdensome and unnecessarily complicated delivery models that restrict doxy-PEP access like those that continue to inhibit HIV treatment and HIV PrEP access in multiple jurisdictions across the country.

We are still in the early days of doxy-PEP use and we need service providers to join with communities affected by Canada’s syphilis epidemic in order to improve access, just like a small yet impactful group of service providers emerged as early HIV PrEP advocates uplifting the health of queer and trans communities. Building upon lessons learned from Canada’s HIV PrEP rollout, you too can step up for the health of our communities, increase doxy-PEP awareness and help decrease syphilis transmission. Faced with the choice between upholding the status quo or acting as an agent of change, I hope you choose change. Our communities are counting on it.


Brook Biggin (he/him) is the director of education, knowledge mobilization and policy at Community-Based Research Centre. Brook is based in Edmonton, Alberta, on Treaty Six Territory, where he has worked in 2SLGBTQIA+ health, HIV, and sexually transmitted and blood-borne infections for the past decade. As a queer person living with HIV, Brook believes in centring the experiences and strengths of 2SLGBTQIA+ communities in our collective efforts to address the syphilis epidemic.


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