DoxyPEP (doxycycline post-exposure prophylaxis)

DoxyPEP is an antibiotic pill taken after sex to help reduce the risk of getting sexually transmitted infections (STIs) like syphilis and chlamydia. ‘Doxy’ means doxycycline, an antibiotic, and ‘PEP’ means post-exposure prophylaxis or for taking after sex.

The main active ingredient in doxyPEP is doxycycline. Doxycycline belongs to a family of antibiotics known as tetracyclines. Doxycycline was originally produced by Pfizer but is now globally produced as a generic antibiotic.

It is commonly used to treat different bacterial infections in the body, but is now being repurposed as a new prophylaxis (disease prevention) treatment to help lower STI risk in the following higher risk groups:

• cisgender gay, bisexual, or other men who have sex with men and transgender women who have sex with men who are high risk due to: a positive STI test in the last year, or having multiple new sexual partners or one off partners, chemsex or group sex in the last 3 months
• transgender men who have sex with men
• Cisgender gay, bisexual, or other men who have sex with men, and transgender women who have both male and cisgender female sexual partners, with a womb and ovaries
• sex workers

Using doxyPEP in this new way does not offer protection against HIV, herpes, hepatitis or other STIs. You should still use condoms for prevention and get tested for STIs if you are experiencing symptoms or you think you might have been exposed to these STIs.

The doxycycline in doxyPEP works by blocking an important protein in bacterial cells from working properly, which stops them from growing and multiplying in the body and causing an infection.

When you take doxyPEP as prescribed within 72 hours of exposure (having unprotected sex), it immediately starts working to stop the bacteria that can cause STIs like syphilis and chlamydia from growing and multiplying in the body.

DoxyPEP works very well in providing protection against STIs like syphilis and chlamydia, and it also works for gonorrhoea, though not as effectively.

A new UK guideline published by BASHH (British Association for Sexual Health and HIV) in 2025 has shows real world data for how well DoxyPEP reduced infection risk. The guideline identifies that doxyPEP lowers:

· syphilis infection risk by 80%

· chlamydia infection risk by 79%

· gonorrhoea infection risk as well, but not as extensively

The effectiveness of doxyPEP for gonorrhoea is not as significant because the bacteria causing gonorrhoea (Neisseria gonorrhoea) has shown an increase in doxycycline antibiotic resistance in recent years.

The effectiveness of doxyPEP can be limited by:

• taking the wrong dose too late or too soon – always take the correct dose as soon as possible. This should be 200mg taken at once (two 100mg pills), within 72 hours of unprotected sex, but preferably within the first 24 hours.
• food and other medications – avoid taking doxyPEP with food and other medications, especially iron supplements and antacids. You should plan to take it on an empty stomach or 2 hours before or after meals.
• drinking large amounts of alcohol – this can reduce its effectiveness and increase the chances of side effects.

DoxyPEP is designed to be taken as a ‘dose on demand’ plan after exposure (having unprotected sex) and not as a continuous daily prescription.

You should take a 200mg dose (two 100mg pills) of doxycycline at once and with plenty of water, sitting upright for at least 30 minutes afterwards to reduce irritation in your throat. It has a higher chance of working better if you take it within 24 hours of unprotected sex but can still be taken up to 72 hours.

DoxyPEP works well when you take it on an empty stomach. Avoid taking it within 2 hours of iron tablets, or antacids. You should also avoid drinking a lot of alcohol when taking doxyPEP as this can reduce how well it works.

If you take more doxyPEP pills than you should, it can increase your risk of side effects. Speak to your doctor as soon as possible if this happens.

How often can you take doxyPEP?

You should not take more than 200mg of doxycycline in a 24-hour period.

If you have taken doxyPEP and have unprotected sex more than once within a 72-hour period, you should take one dose at the end of this time frame rather than multiple doses.

What if doxyPEP doesn’t work?

DoxyPEP is not 100% effective at preventing STIs and doesn’t offer protection against all STIs. This means you should get tested for STIs if you develop symptoms or you think you might have been exposed to a viral STI, even after taking doxyPEP.

You should also check you are taking doxyPEP as prescribed by your doctor, and within 72 hours of unprotected sex.

DoxyPEP dosage

The prescription for doxyPEP is 200mg (two 100mg pills) of doxycycline to be taken at once within 72 hours of unprotected sex. You should not take more than this dosage in a 24-hour period.

You can request doxyPEP online from UK-registered providers like ZAVA. Simply complete our brief online consultation form for one of our doctors to review and check if the treatment is suitable for you. If it is right for you, our doctors will prescribe the treatment, and we can deliver it to your door.

Can I buy doxyPEP over the counter?

No, you cannot buy doxyPEP over the counter. It is an antibiotic, which means you will need a prescription from a doctor first. A doctor can review your circumstances and health and check if it is suitable for you before giving you a prescription.

Can I get doxyPEP on the NHS?

DoxyPEP is currently being rolled out across NHS sexual health clinics in the UK, but it will still take some time to be available in all regions. Speak to your local sexual health clinic to find out if it is available in your region.

Like all medicines, doxyPEP may cause some side effects but not everyone will get them.

Some common doxyPEP side effects are:

• headaches
• nausea
• vomiting
• signs of photosensitivity, like rashes and heightened skin reactions
• heart inflammation
• a systemic lupus erythematosus flare up, which is an autoimmune condition

Some uncommon and rare doxyPEP side effects are:

• anxiety
• heartburn
• bowel inflammation
• flushing of the skin
• tinnitus, which is a ringing in ears
• itching in the genital area
• change in appetite
• skin discolouration
• stomach pain
• liver inflammation
• diarrhoea

If you experience any of the following serious side effects when taking doxyPEP, stop taking the medication and seek immediate medical attention:

• very severe headache which may be accompanied by double or blurred vision
• severe stomach pain
• bloody diarrhoea
• severe blisters of the skin, mouth, eyes and genitals
• low blood pressure and fast heartbeat (palpitations)
• symptoms of a blood disorder including bruising easily, fatigue, and frequent infections
• hypersensitive skin reaction to sunlight – severe sunburn
• yellowing of your skin or eyes
• symptoms of a severe allergic reaction including sudden wheeziness, difficulty in breathing, chest pain, fever, swelling of eyelids, face or lips, rash, or itching, especially affecting the whole body

The full list of known doxyPEP side effects can be found in the patient information leaflet included with your medication.

What to do if you get doxyPEP side effects

Some doxyPEP side effects may resolve sooner as it is taken ‘on demand’ and when you need it, and not continuously or every day.

There are a few things you can try to help manage some side effects at home, for:

• headaches – try increasing water intake and taking painkillers like paracetamol or ibuprofen. If they persist or become severe, speak to your doctor.
• nausea (feeling sick) – eat plain foods and avoid food triggers.
• heartburn – avoid food triggers like spicy foods and caffeine, try taking antacids.

Speak to your doctor if you are unable to manage any side effects at home or if they are bothering you.

DoxyPEP is now recommended if you are:

• over 18
• a gay, bisexual, trans man, or any other man who have sex with other men
• a trans woman who has sex with men, cisgender women, or other other partners with a womb and ovaries
• living with HIV
• at increased risk of getting STIs, for example if you have group sex, chemsex (sex on drugs), multiple sexual partners, or regular or occasional one-off partners
• a sex worker
• at increased risk of syphilis

You should not take doxyPEP if you are:

• under 18
• pregnant
• breastfeeding
• allergic to doxycycline or any other tetracycline family of antibiotics

Tell your doctor about any medical conditions you have been diagnosed with before taking doxyPEP as it may not be suitable for you if you have:

• a liver or kidney condition
• systemic lupus erythematosus or myasthenia gravis
• problems with alcohol dependence
• oesophagitis
• systemic lupus erythematosus (SLE)
• HIV
• benign intracranial hypertension
• porphyria
• proctitis

DoxyPEP and other medications

You should tell your doctor about all medications you are currently taking including herbal or over-the-counter medications before taking doxyPEP. This is because doxyPEP may affect how well some medications work, and some medications may affect how well doxyPEP works.

Before taking doxyPEP, you should tell your doctor if you are on treatment for acne, epilepsy, take warfarin, lithium or rifampicin, or take medications that lower the immune system.

You should tell your doctor if you are taking antacids as you will need to adjust when you take them when you take doxyPEP.

You should not take doxyPEP if you:

• are taking penicillin for infection
• have the anaesthetic methoxyflurane

The full list of known cautions and medicine interactions linked with doxyPEP can be found in the patient information leaflet that comes with your medication.

Some other approaches to help reduce the risk of STIs and transmission include:

• using condoms
• speaking to your doctor or local sexual health clinic about HIV pre- and post-exposure prophylaxis treatments
• regular STI testing
• STI treatment if you test positive
• Vaccinations, such as hepatitis, HPV and Bexsero, if eligible

At ZAVA we offer post exposure prophylaxis (PrEP) treatment service as well as STI testing services.

Can you take doxyPEP and PrEP at the same time?

Yes. DoxyPEP is taken as an ‘on demand’ pill after having unprotected sex to reduce the risk of getting STIs like syphilis and chlamydia. PrEP (pre-exposure prophylaxis) is a daily or ‘on demand’ pill taken by at-risk, HIV-negative people to reduce the risk of getting HIV.

People taking PrEP or living with HIV can also take ‘on demand’ doxyPEP to reduce their risk of getting bacterial STIs like chlamydia and syphilis. If you have HIV, chat to your specialist team about whether doxyPEP would be right for you.

Is doxyPEP the same as doxycycline?

Yes. ‘Doxy’ means doxycycline and ‘PEP’ means post exposure prophylaxis. Doxycycline is the medication and PEP is the method of treatment – emergency treatment after exposure during sex.

Can I take doxyPEP if I have symptoms of an STI?

DoxyPEP is taken after unprotected sex to reduce the risk of getting STIs. If you notice you have symptoms of an STI, you should get tested as soon as possible so you can get the right treatment course. If you have a fever, unexpected vaginal bleeding or stomach or bottom pain or discharge contact your GP or local sexual health clinic promptly as these can be symptoms of a more serious infection.

We offer a range of STI test kits at ZAVA, which you can buy online.

Do I still need STI testing?

Yes. Taking doxyPEP does not offer protection against all STIs. If you are experiencing symptoms of an STI or have unprotected sex, you should get tested as soon as possible for STIs.

You can find more information on STI symptoms in our guides:

• STI symptoms in men
• STI symptoms in women

We offer a range of testing services at ZAVA, which you can request online. Test discreetly at home with an STI test kit from ZAVA. Our range of test kits include:

• extended STI test kits – full STI testing kits for chlamydia, herpes, gonorrhoea and more
• chlamydia and gonorrhea test kits
• syphilis test kits
• chlamydia test kits
• anal chlamydia and gonorrhea test kits
• oral chlamydia and gonorrhea test kits
• MSM test kits, for men who have sex with men
• STI test kits for women

Will doxyPEP treat viral STIs?

No. DoxyPEP does not treat or offer protection against viral STIs as it is an antibiotic. It mainly offers protection against bacterial STIs like syphilis and chlamydia.