Doxycycline (Doxy) PEP and PrEP

As we receive new and up-to-date information about Doxycycline, we are committed to keeping this content current. We appreciate your understanding and encourage you to check back periodically for the latest updates.

What is Doxy?

Doxy, short for Doxycycline, is an antibiotic used to treat various bacterial infections, including sexually transmitted infections (STIs) such as chlamydia and syphilis.

What Is DoxyPEP and DoxyPrEP? 

Doxycycline used as post-exposure prophylaxis (PEP) and pre-exposure prophylaxis (PrEP) are tools that can prevent infection.

When taken before or after coming into contact with a pathogen (like a virus or bacteria), they can decrease a person’s chances of developing infection.

In our context, PEP involves taking medication after sex where we might come into contact with STIs.

PrEP involves taking medication regularly so it is already in our system when we come into contact with STIs.

Who is DoxyPEP for?

DoxyPEP is for anyone who is sexually active and might come in contact with syphilis and gonorrhea—this includes gay, bisexual, and queer men, as well as gender diverse people and trans folks (though more research is needed around its efficacy for trans men). DoxyPEP works for people living with HIV as well as people who are HIV-negative.

Is it Available Yet? 

As of December 1, 2023, post exposure prophylaxis doxycycline (doxyPEP) is available at no cost for some folks accessing HIV PrEP though the provincial HIV PrEP program offered by the BC Centre for Excellence (BC-CfE).

Persons meeting all of the following criteria are eligible to access Doxycycline for PEP through BC-CfE:

  • Currently accessing HIV PrEP, ARVs, or HIV medication, through the BC Center for Excellence, and
  • Identifies as gay, bisexual or other man who has sex with men, or transgender woman, and
  • Is at increased risk of B-STI as indicated either by having a history of B-STI such as syphilis, chlamydia, or gonorrhea within the past year, or being clinically assessed as being at increased risk
  • Current BC resident with BC Medical Services Plan coverage or Interim Federal Health coverage

For further information, contact the BC-CfE Drug Treatment Program office at 604-806-8515.

Other Ways to Access Doxy 

Some people have access to Doxycycline for PEP and/or PrEP because they are participating in research about DoxyPEP and/or PrEP. The DISCO study is comparing DoxyPEP to DoxyPrEP in participants across Canadian urban centres, including Vancouver.

If you are interested in participating in the DISCO study and want to learn more, visit:

How Effective is DoxyPEP? 

Research on DoxyPEP continues, but several studies to date have shown that it is highly effective against several bacterial STIs. It consistently reduced infections of chlamydia and syphilis by more than 70%, while also reducing infections of gonorrhea to a lesser degree.  

Is DoxyPEP Right for Me? 

Almost all of the research done on the effectiveness of DoxyPEP has focused on cis gay, bi, and other men who have sex with men, and transwomen, who are also, in general, disproportionately impacted by the bacterial STIs that DoxyPEP is effective at preventing. Those same bacterial STIs are easily transmitted by many kinds of sex without a condom, including anal, oral, and vaginal or fronthole sex, whether giving or receiving. We recommend speaking with your trusted healthcare professional or a nurse at a HIM Sexual Health Centre about whether DoxyPEP is a safer-sex tool that is best for you, especially if you’ve had a case of chlamydia, syphilis, or gonorrhea in the previous year. 

How Do I Take DoxyPEP? 

The trusted medical professional who prescribes you DoxyPEP is the best person to speak to about how to take DoxyPEP and whose guidance you should follow. Clinical guidelines have still not been published in Canada, but in the supporting research and according to guidelines that have been released elsewhere, DoxyPEP is taken as two 100mg pills of doxycycline (200mg total) no later than 72 (and ideally within 24) hours after oral, anal, or vaginal/front hole sex without a condom. It can be taken as often as once a day, taking no more than 200mg within 24 hours. 

DoxyPEP should be taken with a full glass of water and you should remain upright (don’t lay down) for 30 minutes afterward. Taking it with food may help to reduce indigestion, a more common possible side effect. It’s important not to take antacids or supplements that contain calcium, iron, or magnesium within two hours before or after taking DoxyPEP. People who are pregnant should not take doxycycline. 

What are Potential Side Effects of DoxyPEP? 

Doxycycline is a common antibiotic that has been widely used for decades, rarely resulting in any serious side effects. The most common are an upset stomach or indigestion and nausea, sensitivity to the sun, and irritation or inflammation of the throat. Taking DoxyPEP with a full glass of water and possibly something to eat, staying upright for 30 minutes afterward, and wearing sunscreen if you’ll be going outside all help to reduce these most common side effects if you find yourself facing them. 

There are no known, clinically relevant interactions between doxycycline and gender-affirming hormone therapy. 

Will DoxyPEP work for me, as a trans person?

Most of the studies on doxy did include trans women in their target populations. In this community, DoxyPEP did seem to be effective similar to the gbMSM population; however, the number of trans women enrolled in the studies were often small which limits the generalizability of the results to all trans women and trans feminine folks.

Unfortunately, the studies did not include (at least not explicitly) trans men who have sex with men, therefore, it is unclear from the evidence if DoxyPEP would be effective for trans men and transmasculine folks. It is theoretically possibly to conceive that trans masculine folks/men who have sex with men could have relatively similar effects, but this is an extrapolation to an unstudied population, therefore, it is less certain.

Will DoxyPEP work for me, as someone living with HIV?

Research shows that DoxyPEP remains highly effective regardless of someone’s HIV status. However, that same research also suggested a slightly lower efficacy for people living with HIV, compared to HIV-negative folks. People living with HIV should consult their doctor or other trusted healthcare professional to make sure it’s a good and safe option for them.

What Comes Next? 

While the results from research completed to date has been consistent and extremely promising, research into DoxyPEP remains ongoing. HIM is committed to making sure that members of our communities have access to the best and latest treatments available and are working with local partners as more results and guidelines are available. If you are interested in getting involved yourself, the DISCO study examining DoxyPEP and DoxyPrEP is recruiting participants in the Vancouver area; more information can be found at 

Other Questions You Might Have! 

What About DoxyPrEP? 

PrEP stands for ‘Pre-Exposure Prophylaxis’, a treatment taken before (‘Pre’) a possible exposure, and so DoxyPrEP refers to taking doxycycline before we have sex, as a daily pill. Most of the research conducted so far has focused on DoxyPEP, not PrEP, and so we still lack the specific data on its effectiveness and how to best take it. There are several studies on DoxyPrEP that are almost done or will soon be published, and as more solid guidance emerges HIM will be there to share that with our communities. 

Are DoxyPEP/PrEP and HIV PEP/PrEP the Same Thing? 

No. While they use the same acronyms of PEP and PrEP they are distinct treatments. Until recently, the only sexual health treatments referred to as PEP and PrEP have been HIV PEP and PrEP, treatments that are highly effective at preventing HIV transmission. Yet, while HIV PrEP and PEP are very effective at preventing HIV transmission they offer zero protection against any other STI. Doxy PrEP and PEP are still being studied, but while they appear to be highly effective at preventing certain bacterial STIs they provide zero direct protection against HIV. These treatments can be taken together to protect against both HIV and certain bacterial STIs, but one doesn’t offer the same kind of protection as the other! 

Could Widespread Use of DoxyPEP Result in Greater Antibiotic Resistance? 

One of the greatest remaining concerns about DoxyPEP is whether it could lead to increased resistance to doxycycline as treatment. While a possibility, the most harmful ways it could happen are not considered likely. Doxycycline is a primary treatment for both chlamydia and syphilis, neither of which have shown any evidence of developing resistance, and because of how those bacteria develop resistance it is not considered likely. Gonorrhea already has a high level of resistance to doxycycline, ranging from 25-70% across the world. For that reason, it is not used as a primary treatment for gonorrhea, and so increased resistance to doxycycline is not an immediate problem. 

We should also remember that doxycycline and other drugs of its class are already used as long-term treatments, ranging from weeks to months, to prevent malaria and Lyme disease and to treat acne, as well as for the treatment of the surging number of cases of chlamydia and syphilis. If there were good enough uptake of DoxyPEP to reduce the population levels of the STIs it helps to prevent it might lead to less doxycycline being consumed overall, due to the lower number of infections needing treatment.  

There are also questions around other bacteria developing resistance to doxycycline, including ‘commensal’ bacteria, those that naturally live on and inside of the human body, which could lead to transmitting the resistance they develop. Resistance in all of these bacteria is a topic that research to date has noted and that ongoing research continues to investigate. 


HIM honours the xʷməθkwəy̓əm (Musqueam), Skwxwú7mesh (Squamish), and səlil̓ilw̓ətaʔɬ (Tsleil-Waututh) Nations, and the territories of many nations on the west coast of Turtle Island, on whose unceded and stolen land we live and work. As uninvited inhabitants, we acknowledge that this space is and always will be Indigenous land.

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