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. Doxycycline is also already commonly prescribed as PEP in the USA to prevent Lyme disease and leptospirosis after suspected exposure. Long-term use of doxycycline is also prescribed as a treatment for acne and as a form of malaria prevention.

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. A survey of European men who have sex with men using HIV PrEP found that 8% of them are already using DoxyPEP. A 2019 survey of men who have sex with men in the UK found that 9% of HIV PrEP users had purchased antibiotics to prevent STI infections. In the absence of a prescription, it is likely that these people are purchasing doxy online to protect themselves against STIs.

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. One proposed explanation for this difference is that DoxyPEP may be less effective in areas where doxycycline-resistant strains of gonorrhoea are common.

Defining ‘effective’: The efficacy of DoxyPEP is typically measured by comparing the rates of bacterial STIs in a group of people taking DoxyPEP compared to a similar group of people not taking DoxyPEP. When we say DoxyPEP is 79% effective at preventing syphilis, we mean that a study found that there were 79% fewer cases of syphilis among people taking DoxyPEP than people not taking it.

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). Based on this data, DoxyPEP may also be useful for transgender women who have sex with GBMSM (and there is evidence to suggest doxy works as PEP in trans women).  

In the UK, the British Association of Sexual Health and HIV (BASHH) currently recommends DoxyPEP for preventing syphilis for people who are most likely to get it. This includes gay and bisexual men and some trans women but also other individuals who might be at higher risk of getting syphilis (See: 11. Is DoxyPEP available on the NHS?) 

A history of bacterial STI diagnosis might be a useful way for someone to assess whether DoxyPEP might be beneficial to them, especially people who may be more likely to acquire an STI but who may not be captured in population data (like sex workers). 

***A note for people with vaginas or front holes (including cis women and trans men) who consider themselves more likely to acquire a bacterial STI: There is currently less evidence about the efficacy of doxy at preventing STIs acquired through receptive vaginal or frontal sex but some studies are starting to show that it works. Because of the lack of data from clinical trials, BASHH (in the UK) does not currently explicitly recommend DoxyPEP for people whose risk of getting an STI is through vaginal/frontal sex (though exceptions might be made on a case-by-case basis. See 11. Is DoxyPEP available on the NHS?). However, in May 2026, on the strength of new studies of DoxyPEP, the San Francisco Department of Health has started to recommend DoxyPEP for cis women, trans men, and other people with vaginas/front holes.*** 

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. One way to minimise the risk of these side effects is to drink a large glass of water with a dose of doxycycline and also to take it alongside a meal or with food. It is also recommended to remain upright (sitting or standing) for 30 minutes after taking a dose to prevent reflux.

Please be aware that if you experience stomach upset (vomiting or diarrhoea, for instance) after using doxy and you take oral contraception (the pill), the pill might not protect you from pregnancy.

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. Some studies have linked declines in the diversity of the human gut microbiome with certain chronic diseases - like diabetes - and weight gain. 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.

Doxycycline use can cause vaginal yeast infections. It is thought that this is also a product of doxy disrupting the normal balance of ‘good’ bacteria in the body. Taking probiotics can help combat the loss of these bacteria and stave off yeast infections. If you do experience a yeast infection while using doxy, you can use normal over-the-counter anti-fungal remedies to help combat this.

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. 

Doxycycline has very few negative interactions with other prescribed drugs but there are some that are significant. Based on NHS guidance about doxycycline, you should avoid taking DoxyPEP or speak to a clinician if you are taking any of the following medications: 

• indigestion remedies (antacids)

• stomach ulcer medicines that contain bismuth such as Pepto-Bismol

• 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 (e.g. isotretinoin and warfarin) 

At the moment, the evidence base for DoxyPEP is primarily based on studies conducted with cisgender gay, bisexual and other men who have sex with men, and transgender women. In both of these demographics, DoxyPEP has been assessed in HIV-negative people who are using PrEP and people who are HIV-positive. Efficacy has been proven for both HIV-positive and HIV-negative people. 

There is currently less data supporting the efficacy of DoxyPEP in people whose risk of STIs comes from vaginal/frontal sex – including cis women and some trans men. However, at the time of writing (May 2026), two new studies involving cis women have recently concluded that DoxyPEP can help protect against STIs. Based on the strength of these findings, the San Francisco Department of Health has started to recommend DoxyPEP for cis women, trans men, and other people with vaginas/front holes. 

Having less data about effectiveness for the kind of sex that you have does not mean DoxyPEP is unsafe to use – but individuals may wish to know what the evidence currently says about the action of doxy as an STI prevention tool for them. For more on this, see section 7: How well does DoxyPEP work? What evidence is there that it works? 

Doxycycline is considered by many clinicians to be safe to use if you are or suspect that you are pregnant but you might want to know that some studies link the use of tetracyclines (the class of antibiotics that doxycycline belongs to) during pregnancy to certain risks to the foetus. You can read more about DoxyPEP and pregnancy below under “25. Can I use DoxyPEP if I’m pregnant or suspect I am?”

he evidence base for DoxyPEP is constantly evolving as more studies - including clinical trials - are conducted. We endeavour to keep this section updated with new, pertinent information as often as is feasible.  

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. Both cisgender men who have sex with men and transgender women have been represented in these trials. 

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

1. IPERGAY: A 2017 study in France that examined the effect of DoxyPEP among 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 and transgender women who had a 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 gonorrhoea infection (i.e. that there were similar proportions of cases of gonorrhoea infection in people who used DoxyPEP and people who didn’t use DoxyPEP in the study). Researchers have suggested that, when compared to other subsequent studies, the reason IPERGAY did not detect any effect of DoxyPEP on gonorrhoea infection was because of high levels of doxycycline-resistant gonorrhoea circulating in France at the time (though, the more recent (and bigger) DoxyVAC study in France did find that DoxyPEP worked in preventing about half of gonorrhoea cases). In contrast, there is little evidence to suggest that chlamydia or syphilis bacteria have developed significant resistance to tetracyclines (the class of antibiotics that doxycycline belongs to), which would explain why estimates of efficacy for these infections does not vary so largely between studies. Gonorrhoea in the UK generally has quite high levels of doxycycline resistance, so it is not clear how exactly effective it might be.  

Studies also found that where DoxyPEP was effective at preventing gonorrhoea infection, it was marginally less effective at preventing gonorrhoea infection in the throat when compared to infection in the rectum or genitals. It is thought that this is because when doxy is excreted from the body, it passes through the rectum or genitals and this is a primary mode of preventing bacterial infection. In studies where people took doses more regularly (e.g. 4 times a week), DoxyPEP was more effective at preventing gonorrhoea infection in the throat - presumably because doxycycline reached higher concentrations in these tissues. 

As of May 2026, there is still less evidence that shows DoxyPEP works to protect people having vaginal/frontal sex against STIs. One study with cisgender women in Kenya, published in 2023, suggested that DoxyPEP may not be effective for cisgender women and, possibly, other people with vaginas or front holes. Since then, however, two further studies with cis women – one in Kenya and one in Japan – found that doxyPEP was effective at preventing bacterial STIs. These studies involved slightly different dosing advice for participants, suggesting that other, flexible ways of using DoxyPEP may be more acceptable (and, therefore, more effective!) in groups other than cis gay and bisexual men. Based on the strength of these findings, the San Francisco Department of Health has started to recommend DoxyPEP for cis women, trans men, and other people with vaginas/front holes. 

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. When antibiotics are overused - for instance, in intensive animal farming or when they are wrongly prescribed - this heightens the risk of bacteria becoming resistant to antibiotics. Widespread antibiotic resistance will make it hard to treat common infections with existing medications.

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 (the class of antibiotics to which doxycycline - the antibiotic used in Doxy PEP - belongs). 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. As the results of IPERGAY - which found that DoxyPEP did not protect against gonorrhoea infection - show, tetracycline resistance could limit the efficacy of DoxyPEP.

Because of this, it is important that we take seriously the possibility that DoxyPEP could have an effect upon antimicrobial resistance. Although experts agree that it is likely to have some impact, the scale and nature of the effect of DoxyPEP uptake is not knowable in advance or guaranteed. This is something that requires careful and ongoing monitoring. Existing studies of DoxyPEP efficacy have already begun to do this. The 2022 Seattle/San Francisco trial, for instance, found an 8% increase in tetracycline resistance in Staphylococcus aureus in DoxyPEP users, a bacteria that lives on the skin and is the cause of staph infection.

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. Even if DoxyPEP does have an impact on antimicrobial resistance in some bacteria, this is not necessarily an immediate cause for concern. For example, while the Seattle/San Francisco trial found evidence of a small increase of tetracycline resistance in Staphylococcus aureus, tetracyclines are not typically used to treat staph infection anyway.

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. For instance, as well as offering protection from a range of STIs, DoxyPEP may also have the added benefit of saving additional costs and resources for healthcare providers needed to treat diagnosed STIs. DoxyPEP used today may prevent an infection that needs to be treated by a longer course of doxycycline tomorrow.

4. DoxyPEP is already commonly prescribed to prevent Lyme disease and leptospirosis. When anxieties are expressed about some uses of DoxyPEP - to prevent sexual transmission of infection in minoritised communities – and not others, this may be because of other, unspoken or unconscious concerns (for instance, moralising about gay sex or sex without condoms or an assumption that certain people care more about things like sex than important issues like antibiotic resistance)

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 (see section 26 of this guide for more on this).

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, anal, vaginal and/or frontal 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 (for instance, after sex parties or when they are having sex with someone who is not their regular partner).

Both doxycycline hyclate and doxycycline monohydrate are appropriate to use. These are the two forms that doxy is available in and they typically come as 100 mg pills (meaning you would take 2 pills as a single dose).

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 - including the contraceptive pill or emergency contraception. If you are going to use DoxyPEP and you use any form of contraception, it is advised that you continue to do so as normal while using DoxyPEP. Please be aware that if you experience stomach upset (vomiting or diarrhoea, for instance) after using doxy and you take oral contraception (the pill), the pill might not protect you from pregnancy.

If you are or suspect you are pregnant, it is strongly advised to discontinue using doxy. Doxycycline used during pregnancy can affect the bone and tooth development of the foetus.

It is recommended that you take your doxy with a big glass of water to help avoid stomach upset. It can also help to take your dose with a meal or some food and to avoid drinking alcohol when using DoxyPEP. Staying upright - sitting or standing - for 30 minutes after taking a dose can also prevent reflux caused by irritation in the oesophagus that some people get when taking doxycycline.

After taking a dose of DoxyPEP, avoid ingesting dairy, calcium, antacids (indigestion remedies) or multivitamins for 2 hours. These can reduce the absorption of doxycycline by the stomach (which would reduce its effectiveness).

Doxycycline can increase the skin’s sensitivity to sunlight. If you’re using DoxyPEP regularly, you should consider using a high SPF sunscreen to prevent burning or rashes caused by sun exposure.

Using doxy can disrupt the normal balance of ‘good’ bacteria in your body and this can have an impact on your gut health and cause vaginal yeast infections. If you are using DoxyPEP regularly, it’s a good idea to consider taking a probiotic to help counter this.

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.

In June 2025, the British Association for Sexual Health and HIV (BASHH) published national clinical guidelines recommending the use of DoxyPEP for people at the highest risk of getting syphilis - especially gay, bisexual and other men who have sex with men (GBMSM) and trans women who have sex with GBMSM. Based on the current evidence (see: 7. How well does DoxyPEP work? What evidence is there that it works?) the BASHH guidelines do not currently explicitly recommend DoxyPEP for people with vaginas or front holes (including many women and trans men). However, the guidance does suggest that DoxyPEP should be made available to anyone who considers themselves to be at an elevated risk of syphilis infection subject to discussion with a prescribing clinician. This could include, for instance, trans men who have sex with men and some sex workers. 

This guidance makes the UK one of only a handful of countries worldwide to have published national and evidence-based clinical guidelines about DoxyPEP. The publication of the BASHH guidelines means that DoxyPEP will likely be made widely available at sexual health clinics soon for people at the highest risk of getting syphilis. Certain clinics - like Mortimer Market Centre in London - are already offering DoxyPEP to eligible patients. If you are interested in getting DoxyPEP from a clinic, we recommend speaking to your preferred sexual health provider to ask whether they have begun to implement BASHH's guidelines.  

The Love Tank conducted our own, informal survey of private medical practices in London to ascertain whether DoxyPEP can be accessed through private clinics. Overall, responses indicated that private prescriptions of DoxyPEP may be provided at the discretion of the clinician but some clinics refuse outright to prescribe. It is recommended that, if you wish to access DoxyPEP privately, you make your own enquiries at your chosen clinic(s) before booking an appointment.

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.

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.

However, it should be noted that acquiring doxy this way requires people to state things about their medical history that may be untrue.

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 2018, 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.

Note that listing of any of the above sites is not an endorsement or recommendation of these sites, nor an indication that The Love Tank has a preferred relationship with any of these sites. These sites were chosen for testing of HIV PrEP because these were the main sources of online HIV PrEP in the UK when testing was undertaken, according to community PrEP surveys.

In addition to purchasing doxycycline through online pharmacies without a prescription, doxycyline can also be purchased at online pharmacies that offer doxycyline as an anti-malarial regimen for people travelling to countries where malaria is a risk. You will not be asked your medical history, only asked to state that you intend to travel to a country where malaria is a risk. You should answer any questions about potential contraindications (e.g. medicines that might negatively interact with doxycycline) as honestly as possible for your safety.

At the time of writing, prices of doxy per 100 mg pill purchased online without a prescription ranged from 0.27p per pill to 0.43p per pill. This puts the cost of 30 doses of doxy (two 100 mg pills) at between £16.20 and £25.80. As of August 2023, prices of doxy at online suppliers were as follows:

PRICE CHART

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.

*This is assuming that 3 months worth of medication is equivalent to taking one dose of doxy (two 100 mg pills) every 24 hours.

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. Doxycycline capsules are less stable than tablets so it is important to act with particular caution if this is the form your doxy arrives in.

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.

The only available evidence about the use of antibiotics as STI PEP is about doxycycline. Currently only doxycycline is recommended and being considered for use as STI PEP by researchers and clinicians.

It is thought that other antibiotics are unlikely to be suitable as STI PEP and, therefore, it is recommended that you don’t use them.

Doxycycline is generally safe to take every day. As such, people who don’t experience significant side effects, or who can tolerate it well, could use Doxy as PrEP (pre-exposure prophylaxis). What this means is, unlike with DoxyPEP where doxy is taken only after sex, people could plausibly take doxy daily so that they are always protected against STI infection. Some researchers think that if doxy is used as daily PrEP, only a 100 mg dose might be neede (instead of a 200 mg dose as is used in DoxyPEP) because of the rate that doxy builds up in and leaves body tissues.  

In January 2025, Canadian researchers published findings from a randomised control trial (a pilot study) that showed a 74% reduction in bacterial STIs in GBMSM and trans women using doxyPrEP (100mg of doxycyline every day) compared to those who weren’t.  

For some people, DoxyPrEP (daily doxycycline) might be a more convenient or suitable option than DoxyPEP (doxycyline after sex). However, more research is required to understand who might benefit from using doxycycline every day (compared to the flexible dosing schedule offered by DoxyPEP), how effective it is compared to DoxyPEP, as well as how more widespread daily use of antibiotics might affect antimicrobial resistance. In part because of this, DoxyPrEP has not yet been formally recommended for use in the UK or elsewhere. 

Yes. HIV PrEP (pre-exposure prophylaxis) is a pill that, if taken every day or before and after sex, can prevent someone who is HIV-negative from acquiring HIV (but not other STIs). You can read more about HIV PrEP, including how to take it and where to access it, here.

We recommend that people who are having, planning or wanting to have sex without condoms consider whether they might want to use HIV PrEP. We think HIV PrEP might be particularly helpful for people who might be more at risk of acquiring HIV through sex - like gay, bisexual and other men who have sex with men and transgender women.

HIV PEP (post-exposure prophylaxis) is also available. If you believe you might have been exposed to HIV - for instance, you had anal sex without a condom and you aren’t on HIV PrEP - you can use HIV PEP to reduce your chances of acquiring the virus. You need to start PEP within 72 hours - three days - of exposure to HIV. It involves taking HIV medication every day for one month after exposure. You can access PEP either at the A&E department of a hospital or a sexual health clinic.

Doxycycline does not interfere with usual hormone treatments (e.g. hormone replacement therapy) in cisgender or transgender people.

Doxycycline does not interfere with the action of contraceptives. However, please be aware that if you use an oral contraceptive (the pill) and experience stomach upset (vomiting or diarrhoea, for instance) after using doxy, the pill might not protect you from pregnancy.

Doxycycline is considered by many clinicians to be safe to use if you are or suspect that you are pregnant. However, if you are pregnant or suspect you are, you might find it important to know that the use of tetracyclines - the class of antibiotics to which doxycycline belongs - is associated with some risks during pregnancy, including impact on the bone and teeth development of the foetus.

 The evidence that specifically links doxycycline to these adverse outcomes during pregnancy is mixed or weak. Some researchers therefore believe it is safe to prescribe doxycycline to people who are pregnant, while others think we need more evidence before we can draw a strong conclusion about this.

Ultimately, if you are pregnant, or suspect you are, you might wish to consider whether the benefits of using DoxyPEP for you outweigh the risks associated with doxycycline. If it’s relevant, you might wish to discuss this with the clinician or doctor who is providing your prenatal care.

You are not under any legal obligation to tell your/a sexual health clinic that you are using DoxyPEP.

You might wish to tell a clinician you are using DoxyPEP if you are prescribed a medication or new medication and you want to make sure that this will not negatively interact with using doxy (this includes medication that you might receive if you test positive for an STI).

If you develop symptoms and subsequently test positive for and receive treatment for an STI while using DoxyPEP, it is recommended that you stop using DoxyPEP until you have completed the treatment provided to you by a clinician (this includes doxycycline prescribed as treatment for an STI).

As well as helping protect individuals from acquiring an STI, DoxyPEP may benefit communities and the wider population by helping limit STI transmission. If doxy stops someone from acquiring an STI this also means they won’t pass it on through sex either. This may be particularly important right now because we have seen increasing numbers of STI diagnoses in the UK in recent years.