This guide was researched, written and edited by Dr Benjamin Weil and Dr Will Nutland. The guide benefited from the advice and guidance of people from queer communities – including people who are already using DoxyPEP. 

What is DoxyPEP?

This guide was researched, written and edited by Dr Benjamin Weil and Dr Will Nutland. The guide benefited from the advice and guidance of people from queer communities – including people who are already using DoxyPEP. 

DoxyPEP – which stands for doxycycline post-exposure prophylaxis – is a tool for preventing certain sexually transmitted infections (STIs). It involves taking a dose of the antibiotic doxycycline (doxy) after sex, which can prevent infection by bacteria that cause STIs. This includes chlamydia, syphilis, gonorrhoea and common but lesser known bacteria like mycoplasma genitalium.

Doxycycline is good for STI PEP because it is relatively cheap, does not interact negatively with many common prescription drugs, is very safe to use for most people, and is already used as treatment for chlamydia and syphilis.

Who is currently using DoxyPEP, and how?

DoxyPEP is currently authorised for prescription in San Francisco and other parts of the US for cisgender men and transgender women who have had a bacterial STI in the past year and who also report having had sex (oral, anal, vaginal and/or frontal) without condoms with at least one cisgender male or transgender female partner in the past year.

DoxyPEP is not currently authorised for prescribed use in the UK. However, a number of studies have found that some people are already taking doxycycline as PEP.

Does DoxyPEP prevent all STIs or only some?

Because it is an antibiotic, DoxyPEP only prevents infection with bacteria and not other things that cause STIs like viruses (including HIV and hepatitis B) or parasites (including crabs and scabies).

The evidence currently available suggests that DoxyPEP is particularly effective at preventing chlamydia (~70-89% effective) and syphilis (~73-87%) infection. Two studies have shown that DoxyPEP is 51-57% effective at preventing gonorrhoea infection but one found that DoxyPEP had no effect on gonorrhoea.

Who might DoxyPEP be useful for?

DoxyPEP may be useful for anyone who is at an elevated risk of acquiring a bacterial STI. This will include people who are less likely to use condoms regularly. According to current UK data, the groups that are more likely to acquire a bacterial STI, and therefore might benefit from DoxyPEP, are: gay and bisexual men and other men who have sex with men (GBMSM); Black communities (especially the Black Caribbean community); and young people between the ages of 18 and 24 (especially young GBMSM).

The San Francisco Department of Public Health currently recommends DoxyPEP for anyone who has a history of bacterial STIs and condom less sex in the past year.

Are there any risks or side effects associated with DoxyPEP?

Doxy is used as STI PEP because it is generally well-tolerated and has very few negative interactions with other prescription drugs. Doxycycline is already prescribed for daily use in the UK to treat acne and also as a form of malaria prevention.

Some people may experience mild side effects when taking doxy as PEP. These include feelings of nausea, headaches, and mild gastrointestinal issues. Different people will experience and tolerate these side effects differently.

Doxycycline can also increase the sensitivity of the skin to sunlight. Wear sunscreen with SPF when using doxy.

Doxycycline use is associated with a loss of some of the ‘good bacteria’ that make up the microbiome of the gut. The microbiome of the human gut is important for a number of things in the body, including digestion and immune health.  No evidence yet links DoxyPEP use to significant declines in the health of the gut microbiome but, nonetheless, people using DoxyPEP should consider taking active steps to preserve their gut health by, for instance, taking probiotics.

Is there anyone who shouldn’t use DoxyPEP?

Doxycycline is generally well tolerated. However, anyone who has a known tetracycline allergy – the class of antibiotics to which doxycycline belongs – should not use DoxyPEP.

  • indigestion remedies (antacids)
  • stomach ulcer medicines that contain bismuth such as Pepto-Bism
  • other antibiotics, such as rifampicin
  • acne medicines containing vitamin A, such as isotretinoin
  • warfarin, a medicine to help prevent blood clots
  • medicines for epilepsy, such as phenytoin or carbamazepine
  • ciclosporin, a medicine that calms down your immune system

Some of these drugs are to be avoided when taking doxy because they can reduce the effectiveness of the antibiotic (e.g. indigestion remedies) while others are to be avoided because doxy can increase the risk of negative side effects associated with the other drug.

How well does DoxyPEP work? What evidence is there that it works?

he evidence base for DoxyPEP is constantly evolving as more studies.

As of June 2023, three initial clinical studies have suggested that DoxyPEP works well at preventing bacterial STIs, including chlamydia, syphilis, gonorrhoea and mycoplasma genitalium. These trials indicate that DoxyPEP is 70-89% effective at preventing chlamydia infection and 73-87% effective at preventing syphilis infection. Two out of the three studies found that DoxyPEP is 51-57% effective at preventing gonorrhoea infection.

The three initial clinical studies that assessed the efficacy of DoxyPEP are:

  1. IPERGAY: A 2017 study in France that examined men who have sex with men who use HIV PrEP.
  2. DoxyPEP: A 2022 study in Seattle and San Francisco (USA) that examined the effect of DoxyPEP in men who have sex with men who ha history of STI infections. Participants in this study either were HIV-negative and used HIV PrEP or were living with HIV.
  3. DoxyVAC: A 2022 study in France that examined the effects of DoxyPEP, as well as the meningococcal B vaccine, in men who have sex with men. Participants in this study were either HIV-negative and used HIV PrEP or were living with HIV.

The 2017 IPERGAY study found that DoxyPEP had no effect on gonorrhea infection.

Researchers have suggested that, when compared to other subsequent studies, the reason IPERGAY did not detect any effect of DoxyPEP on gonorrhea infection was because of high levels of doxycycline-resistant gonorrhea circulating in France. Gonorrhea in the UK generally has quite high levels of doxycycline resistance, so it is not clear how exactly effective it might be.

What about antibiotic/antimicrobial resistance?

Antibiotic/antimicrobial resistance is currently a widespread public health concern. The WHO has named it as “one of the biggest threats to global health, food security, and development today.” Antimicrobial resistance occurs when bacteria that cause infections acquire genetic material that means they are no longer affected by antibiotics that normally kill them.

Chlamydia and syphilis – two of the STIs that DoxyPEP is considered very effective at protecting against – currently show very few signs of resistance to tetracyclines.  However, there are some concerns about DoxyPEP causing an increase in antimicrobial resistance because:

  1. Some people consider long-term use of doxycycline to be a form of overuse
  2. Tetracyclines are commonly used antibiotics. Some common bacteria, including E. coli, have already developed widespread tetracycline resistance
  3. Some of the bacteria that cause gonorrhoea infection already demonstrate antimicrobial resistance.

It is important that we take seriously the possibility that DoxyPEP could have an effect upon antimicrobial resistance.However, there is no reason that the possibility of antimicrobial resistance should necessarily stop people using or having access to DoxyPEP today. There are a number of reasons for this.

  1. As has been suggested above, the effects of DoxyPEP on resistance are not a given and will vary depending on uptake. This requires monitoring rather than avoidance.
  2. DoxyPEP is only recommended for use in populations who are at elevated risk of STI infection, which will limit the use of the antibiotic.
  3. Given the current knowledge about levels of resistance, the benefits of offering DoxyPEP to people at elevated risks of STIs outweighs the costs.
  4. DoxyPEP is already commonly prescribed to prevent Lyme disease and leptospirosis.

The bottom line is that some people who are at higher risk of acquiring an STI may benefit from DoxyPEP – whether because it can give them peace of mind about having sex without condoms or because it will reduce the risk of them developing a symptomatic STI. Antimicrobial resistance is a real concern but, without clear ongoing evidence of DoxyPEP’s impact, this does not necessarily outweigh the potential benefits to individuals and communities that the tool might have.

How is Doxycyline usually used as PEP?

When DoxyPEP is used, it is recommended that you take 200 mg – two 100 mg pills – of doxycycline within 24 hours – and not later than 72 hours – after condomless oral, and anal sex. One 200 mg dose (2 x 100mg) of doxy will cover all of the sex you have had in a 72 hour period. That means if you had lots of sex on Saturday and Sunday – and you didn’t use doxy on those days – you could take a dose on Monday and it would provide some protection against STI infection for the sex that you had over the weekend.

If you have sex again soon after taking a dose, don’t take another dose immediately – wait another 24 hours after your last dose to take it. You shouldn’t take more than 200 mg of doxycycline in a 24 hour period.

As long as they use it within 72 hours of sex and no more than once in a 24 hour period, people can choose to use doxy as regularly or irregularly as they like. Some people might choose to use it to protect themselves every time they have sex and others might only choose to use it on particular occasions.

While you are using doxy it is strongly recommended that you continue to follow your usual sexual and reproductive health regimen, including (as applicable): taking your normal HIV medication; daily or event-based dosing of HIV PrEP; using condoms; using your usual contraceptives; and testing for STIs as regularly as every three months.

Doxy does not interfere with the action of any form of contraception

How often and for how long can DoxyPEP be used?

You can use DoxyPEP as often as every day but you shouldn’t take more than 200 mg of doxy in a 24 hour period.

Is DoxyPEP available on the NHS?

At the time of writing (August 2023), there are no clinical trials underway in the UK to assess the efficacy, safety or feasibility of DoxyPEP provision. Given the current international attention being paid to DoxyPEP, it is possible that NHS policy regarding prescribing of DoxyPEP will be reconsidered in the near future.

How much will it cost?

A prescription authorised by a private clinician may be paid for in any pharmacy. You will be charged the full cost price of the medication. This is likely to be more than the set cost of an NHS prescription, which is £9.65. The cost of private consultations varies between clinics (and some clinicians may require repeat consultations before prescribing). Prices cited to The Love Tank ranged from £60 – £295.

 How else can you access DoxyPEP in the UK?

We know that some people are getting doxy through high street pharmacies like Boots and Superdrug. To do this, people are using online services provided by these pharmacies and either self-reporting as having chlamydia or stating that they have had a sexual contact who has recently tested positive for chlamydia. Using these services, people are able to acquire a course of doxy prescribed for the treatment of chlamydia infection (usually 14 x 100 mg pills of doxycycline – or seven 200 mg doses) at a cost of around £18.

Can DoxyPEP be bought online?

Many people who are using DoxyPEP are doing so without a prescription by purchasing generic doxy from online suppliers (some of the same ones that people use to access generic HIV PrEP).

In 2016, PrEPster independently tested generic HIV PrEP to assess its legitimacy and safety. Regarding their tests of HIV PrEP purchased from Dynamix International; Green Cross Pharmacy; In House Pharmacy; and United Pharmacy, they concluded that “we can be very confident that the PrEP we’re buying online is safe and genuine, from the sources that were tested.” All of the websites named here also sell generic doxy at a relatively affordable price.

What does the law say about buying DoxyPEP online?

In the UK, it is legal to import up to 3 months worth of some classes of medication for personal use. This means it is legal to import up to 90 doses (or 180 100 mg capsules) of doxy* provided you do not share this with, intend to share this with, or sell this to others.

How do we know if doxycycline purchased online is legitimate or safe?

While PrEPster at The Love Tank have previously tested generic HIV PrEP purchased from online suppliers (which suggests they can be trusted), it is not entirely possible to know whether doxy purchased online is legitimate without conducting tests on the product. However, doxycycline is a fairly cheap drug to manufacture and purchase in generic form. Therefore, unlike other more expensive drugs, it is unlikely to be a target for counterfeits or tampering (as the profit margin would be low).

Doxycycline should always be stored at room temperature (below 30 degrees celsius) in an airtight container and protected from light. Although it is sometimes not possible to know, if you have reason to believe that one or more of the packets/containers of doxy you have purchased online have not been stored appropriately – for instance if the packaging is damaged, wet, or is loose in unsterile packaging (like an envelope) discard the packet(s)/container(s) and do not take any of the pills within it.

It is not safe to take doxycycline after its expiry date. Doxycycline taken past its expiry date can cause kidney damage. If your doxy is past its expiry date or does not have an expiry date labelled on it, discard it.

Can other antibiotics be used as STI PEP?

The only available evidence about the use of antibiotics as STI PEP is about doxycycline. Currently only 

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What is DoxyPEP?

DoxyPEP is a post-exposure preventative treatment for syphilis, chlamydia, and gonorrhea. Think of it as a morning-after pill but for bacterial STIs instead of pregnancy: take one dose after a condomless sexual encounter to greatly reduce your risk of contracting bacterial STIs.

DoxyPEP does NOT help prevent:

  • HIV
  • Mpox (monkeypox)
  • Other viral infections

Who should consider DoxyPEP?

You should consider DoxyPEP if you were assigned male at birth, are at least 12 years old, and:

  • Have been diagnosed with at least one bacterial STI (i.e., chlamydia, gonorrhea, syphilis) in the last 12 months
  • Have had condomless oral and/or anal sexual contact with at least one individual assigned male at birth in the last 12 months

Although current research has shown that DoxyPEP is only effective for people meeting these criteria, we know that people who haven’t had a recent STI or were assigned female at birth may still be interested in adding DoxyPEP to their STI prevention toolkit. We encourage anyone who believes they may benefit from DoxyPEP to discuss the risks and benefits with their Howard Brown provider to see if it may be an option for them.

How can I get DoxyPEP?

  1. Make sure you’re eligible to take DoxyPEP (see “Who should consider DoxyPEP?” above)
  2. Schedule a routine primary care visit at a Howard Brown Health location
  3. Tell your scheduler or indicate in your online submission that you’re interested in starting DoxyPEP
  4. Attend your appointment: the provider will do STI testing and basic bloodwork to confirm your eligibility
  5. Once your test results come back and your eligibility is confirmed, we will provide you with a doxycycline prescription
  6. Pick up your prescription at a Howard Brown pharmacy (or your local pharmacy)
  7. Keep the bottle in your medicine cabinet or on your nightstand until you need it!

How do I take DoxyPEP?

Just remember that it’s 3, 2, 1!

Within three days, take two tabs, just one time

In other words:

  • Within 3 days, or 72 hours, of a condomless sexual encounter
  • Take 2 tablets, or 200 mg, of Doxycycline
  • Just 1 time, or no more than one dose per day

When taking DoxyPEP, you should also keep in mind that:

  • It will be most effective if you take it within the first 24 hours, so treat it like a morning-after medication
  • Although it is safe to take daily, do not take more than 200mg in one day
  • Take it with 8 oz of water and food, if possible, to help decrease any potential side effects like nausea or headaches
  • Some people are more sensitive to the sun when they take it, so be sure to wear sunscreen and/or stay covered when spending extended time outdoors

What else should I know before starting DoxyPEP?

  • It is safe to take PrEP for HIV and DoxyPEP at the same time.
  • DoxyPEP treatment is not 100% protective, but recent studies have shown that it can decrease your likelihood of contracting syphilis, chlamydia, and gonorrhea by about 60%.
  • Since this treatment method is relatively new, we are still learning about the effects of DoxyPEP on the ‘good’ bacteria of the gut, the bacteria that live on our skin (for example, staph), and possible resistance to STIs such as gonorrhea.
  • Doxycycline is not a new medication, but this use of it is. Doxycycline has long been used as a common antibiotic due to its safety, mild potential side effects, and low cost.
  • Chlamydia and syphilis have shown no resistance to doxycycline, despite it having been used as a common antibiotic for decades.

What should I know for after I start DoxyPEP?

  • Patients taking DoxyPEP will need to follow-up with their primary-care provider every three months for routine STI testing, standard bloodwork, and refills on the DoxyPEP prescription.
  • If you are having symptoms of an STI while taking DoxyPEP or have a known exposure to an STI, please come in to get tested and treated – otherwise, continue your routine testing every three months.
  • We may reach out to you via MyChart at some point in the months after your start DoxyPEP to ask about your experience with it. This helps us to learn more about the patient experience with it so we can make any needed adjustments or improvements to how we offer DoxyPEP.