Azithromycin for STIs: Which Infections It Treats and When It Isn’t Used
Where azithromycin fits in UK treatment of chlamydia, Mycoplasma genitalium and urethritis — and the infections it’s no longer used for.
Part of our Chlamydia condition guide.
Get urgent help first. Go to A&E or call 999 for sudden, severe pain in a testicle, or severe pain low in your tummy with a fever, fainting or any chance you could be pregnant. Contact NHS 111 (NHS 24 on 111 in Scotland) or your GP the same day for pelvic pain, pain during sex, bleeding between periods or after sex, or a fever with genital symptoms. Online treatment isn’t suitable in these situations.
The short answer: azithromycin still has a role in treating some sexually transmitted infections, but in the UK it’s no longer the first choice for any of them. The course depends on the infection, a single 1g dose is no longer recommended for urethritis or Mycoplasma genitalium, and it isn’t used for gonorrhoea or syphilis.
Tested Positive for Chlamydia? Get Treated Online
Access Doctor is a GPhC-registered pharmacy (#9011198). If you’ve tested positive for chlamydia, or a sexual partner has, a pharmacist independent prescriber reviews your online consultation and prescribes treatment if it’s suitable for you. Dispensed from our UK pharmacy. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start Chlamydia Consultation →Adults only online. Access Doctor’s online chlamydia service is for adults aged 18 and over who aren’t pregnant or breastfeeding. If you’re under 18, pregnant or breastfeeding, an NHS sexual health clinic or your GP can test and treat you free and in confidence — and under 25s can also get help from Brook.
Which STIs azithromycin is used for
Azithromycin is a macrolide antibiotic. It builds up inside cells and lingers in the body for several days after the last dose, which makes it handy against bacteria that live inside cells — chlamydia being the classic example. But resistance and newer evidence have changed its role. This table sets out current UK guidance.
| Infection | Usual UK first choice | Azithromycin’s role |
|---|---|---|
| Chlamydia (genitals or throat) | Doxycycline 100mg twice a day for 7 days | Alternative if doxycycline can’t be taken |
| Chlamydia (rectum) | Doxycycline 100mg twice a day for 7 days | Less effective; used only if doxycycline can’t be taken |
| Mycoplasma genitalium | Doxycycline for 7 days, then azithromycin for 3 days if the bacteria aren’t resistant | Second stage of treatment, guided by resistance testing |
| Non-gonococcal urethritis | Doxycycline 100mg twice a day for 7 days | Alternative 3-day course |
| Gonorrhoea | Ceftriaxone injection | Not used |
| Syphilis | Penicillin injection | Not used |
| Pelvic inflammatory disease | Ceftriaxone injection, then doxycycline and metronidazole for 14 days | Not part of the standard regimen |
Sources: BASHH guidelines for chlamydia (2026), Mycoplasma genitalium (2025), NGU (2026), gonorrhoea and PID; NICE CKS.
Chlamydia
Azithromycin was the go-to treatment for chlamydia until 2018, when UK guidance switched to doxycycline — it works slightly better for genital infection and clearly better for infection in the rectum. Azithromycin is now used for people who can’t take doxycycline, for example because of an allergy to tetracyclines.
NICE CKS and the national NHS patient group direction use a 3-day course: 1g on day 1, then 500mg once a day on days 2 and 3. The product licence gives a single 1g dose, so the 3-day course is prescribed off-label — which is common, accepted practice in sexual health. BASHH’s 2026 chlamydia guideline also allows a single 1g dose. Your prescriber will tell you exactly which course to take.
Our guide to azithromycin for chlamydia covers how to take it, side effects and what to do afterwards.
Mycoplasma genitalium
Mycoplasma genitalium (often called Mgen or MG) is a sexually transmitted bacterium that can cause urethritis in men, and cervicitis and PID in women. Many people who have it have no symptoms, and UK guidance is to test only people with symptoms, or the partners of people who have it.
Mgen has become very resistant to azithromycin. In England, about two-thirds of samples tested in 2025 carried genetic changes linked to macrolide resistance (UKHSA). That’s why azithromycin is no longer used on its own, and why a single 1g dose is out: it’s less likely to cure the infection and more likely to breed resistance.
Current UK treatment (BASHH Mgen guideline, 2025): for uncomplicated infection, doxycycline 100mg twice a day for 7 days, then, if the bacteria aren’t known to be resistant, azithromycin 1g on day 1 followed by 500mg once a day for 2 days. If resistance is found, or azithromycin doesn’t work, a different antibiotic, moxifloxacin, is used after the doxycycline. PID or epididymo-orchitis caused by Mgen needs a longer course.
Mgen is managed by sexual health clinics. It needs specialist testing, often including a resistance test, and follow-up. If you’ve been treated and your symptoms haven’t settled, don’t repeat azithromycin — go back to the clinic. Access Doctor doesn’t treat Mgen online.
Non-gonococcal urethritis (NGU)
NGU means inflammation of the urethra (the tube urine passes through) that isn’t caused by gonorrhoea. It usually causes stinging when peeing or discharge from the penis. Chlamydia and Mycoplasma genitalium are common causes, though often no cause is found.
Under the 2026 BASHH guideline, the first choice is doxycycline 100mg twice a day for 7 days. Azithromycin is an alternative, as a 3-day course of 1g then 500mg once a day for 2 days; a single 1g dose is no longer recommended. After azithromycin, avoid sex until 14 days after starting treatment, until your symptoms have gone, and until partners have been treated. NGU is diagnosed with a microscope test at a sexual health clinic, so that’s where it’s treated.
Infections azithromycin isn’t used for
Gonorrhoea
Gonorrhoea is now commonly resistant to azithromycin. UK treatment is a single ceftriaxone injection at a sexual health clinic, followed by a test to check it has gone.
Syphilis
Resistance to azithromycin is widespread in syphilis. Penicillin injections remain the treatment, given by a sexual health clinic.
Pelvic inflammatory disease
PID needs an examination and a broader combination: usually a ceftriaxone injection, then doxycycline and metronidazole for 14 days.
Viral STIs
Antibiotics don’t touch herpes, HPV (genital warts) or HIV. These need different treatments from a clinic or GP.
Pregnancy and breastfeeding
Doxycycline isn’t used in pregnancy, so azithromycin is one of the antibiotics NHS services use to treat chlamydia in pregnant women, with a test afterwards to check it worked. This is managed by your midwife, GP or a sexual health clinic. Access Doctor doesn’t treat chlamydia online during pregnancy or breastfeeding. See our chlamydia in pregnancy guide.
Why the right course matters
The azithromycin course for chlamydia, for Mycoplasma genitalium and for a chest or throat infection aren’t the same, and the wrong course can fail or encourage resistance. Never use leftover tablets, or tablets prescribed for someone else, to treat yourself or a partner. If your symptoms come back or don’t settle after treatment, get retested rather than taking another course: reinfection from an untreated partner, Mgen, gonorrhoea or trichomonas could be the cause.
Side effects and safety
Azithromycin is usually well tolerated. Diarrhoea is very common, and feeling sick, being sick, tummy pain and headache are common (product information). Rarely, it can affect heart rhythm, so tell your prescriber about any heart condition, a family history of sudden death, or other medicines you take. It can also interact with medicines such as warfarin, digoxin, colchicine and ciclosporin.
Our azithromycin guide covers side effects, interactions and who shouldn’t take it in full.
Getting treated
Access Doctor’s online service treats uncomplicated chlamydia in adults aged 18 and over who have tested positive, or whose sexual partner has. Doxycycline is the usual choice, with azithromycin for people who can’t take it. For urethritis, Mycoplasma genitalium, gonorrhoea, PID, or symptoms without a test result, please see an NHS sexual health clinic, which is free and confidential. Our chlamydia treatment online page explains how our service works.
UK safety, support and free NHS options
Doxycycline and azithromycin are prescription-only medicines in the UK. Before anything is prescribed, a GPhC-registered pharmacist independent prescriber reviews your consultation, including your allergies and the other medicines you take. Always read the patient information leaflet in the pack. Never share antibiotics with anyone else, even a partner with the same infection, and don’t keep leftovers for another time: return unused tablets to a pharmacy.
If you think you’ve had a side effect from a medicine, tell your pharmacist or doctor. You can also report it to the MHRA through the Yellow Card scheme, which helps keep medicines safe for everyone.
NHS sexual health clinics test and treat chlamydia free of charge across the UK, and you don’t need a GP referral: use the NHS website in England, NHS inform in Scotland, Sexual Health Wales in Wales and nidirect in Northern Ireland to find one. Our private chlamydia treatment online service is an alternative for adults aged 18 and over.
If anything about how you got this infection doesn’t feel right — for example, if sex wasn’t your choice, or a partner pressures or controls you — you can talk to someone in confidence. See support, if you need it for free, confidential helplines. If you’re in immediate danger, call 999.
Frequently Asked Questions
Can azithromycin treat gonorrhoea?
No. Gonorrhoea is now commonly resistant to azithromycin, and UK guidance is a single ceftriaxone injection given at a sexual health clinic. If you’ve been diagnosed with gonorrhoea, or a partner has, go to a sexual health clinic for treatment and a test afterwards.
Does azithromycin treat Mycoplasma genitalium?
Sometimes, but not on its own. UK guidance is doxycycline for 7 days first, then a 3-day azithromycin course if the bacteria aren’t resistant. About two-thirds of samples tested in England in 2025 showed resistance to azithromycin, so clinics often test for this and use moxifloxacin instead.
Why is doxycycline preferred over azithromycin for chlamydia?
Studies show doxycycline cures slightly more genital infections and clearly more rectal infections than azithromycin. Since 2018, UK guidance has recommended doxycycline 100mg twice a day for 7 days first, with azithromycin kept for people who can’t take doxycycline.
Is a single 1g dose of azithromycin still used?
It depends on the infection. For chlamydia, the product licence and BASHH’s 2026 guideline allow a single 1g dose, while NICE CKS and NHS services use a 3-day course. For non-gonococcal urethritis and Mycoplasma genitalium, a single 1g dose is no longer recommended. Your prescriber will tell you which course to take.
Can I take azithromycin for chlamydia if I’m pregnant?
Azithromycin is one of the antibiotics NHS services use for chlamydia in pregnancy, because doxycycline isn’t used. Treatment in pregnancy is managed by your midwife, GP or a sexual health clinic, with a test afterwards. Our online service doesn’t treat chlamydia during pregnancy.
What if my symptoms continue after azithromycin?
Don’t take another course. Ongoing symptoms can mean reinfection from an untreated partner, a different infection such as Mycoplasma genitalium, gonorrhoea or trichomonas, or a cause that isn’t an infection. See a sexual health clinic for retesting.
How long after azithromycin can I have sex?
For chlamydia, wait until you and your partner have both finished treatment, and until 7 days after your last azithromycin tablet. For urethritis or Mycoplasma genitalium, BASHH advises waiting until 14 days after starting treatment and until your symptoms have gone.
Chlamydia treatment from Access Doctor
If you’ve tested positive for chlamydia, or a sexual partner has, and you’re 18 or over and not pregnant or breastfeeding, our pharmacist independent prescribers can assess you online.
Antibiotic · Rx · usual first choice
Doxycycline 100mg capsules
7-day course: one capsule twice a day. Prescribed after an online consultation.
View product →Antibiotic · Rx · if you can’t take doxycycline
Azithromycin 500mg tablets
3-day course for people allergic to, or unable to take, doxycycline. Prescribed after an online consultation.
View product →References
- British Association for Sexual Health and HIV (BASHH). UK national guideline for the management of infection with Chlamydia trachomatis, 2026 (Saunders J, et al.). doi.org
- Soni S, Fifer H, Al-Shakarchi Y, et al. British Association for Sexual Health and HIV national guideline for the management of infection with Mycoplasma genitalium, 2025. Int J STD AIDS. doi.org
- UK Health Security Agency. Mycoplasma genitalium antimicrobial resistance surveillance (MARS) report, 2025. gov.uk
- Crofts M, Blee K, Evans C, et al. British Association for Sexual Health and HIV national guideline on the management of non-gonococcal urethritis (NGU), 2026. Int J STD AIDS. doi.org
- Fifer H, Saunders J, Soni S, et al. 2018 UK national guideline for the management of infection with Neisseria gonorrhoeae (BASHH). Int J STD AIDS. 2020;31(1):4–15.
- BASHH. UK national guideline for the management of pelvic inflammatory disease, 2019 interim update (Ross J, et al.).
- NICE Clinical Knowledge Summaries. Chlamydia – uncomplicated genital. cks.nice.org.uk
- Azithromycin for chlamydia: national patient group direction template, version 3.1, April 2026. communitypharmacy.org.uk
- Electronic Medicines Compendium. Azithromycin 500mg tablets: Summary of Product Characteristics. medicines.org.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.