How to Take Metronidazole: Dosage, Timing and Alcohol
The practical rules for getting through a course — when to take it, what to avoid, and what to do if you slip up.
Part of the Bacterial Vaginosis condition guide.
Get medical help first. Contact NHS 111 (NHS 24 on 111 in Scotland) or your GP the same day if you have pain in your lower tummy or pelvis, a high temperature or you feel unwell. If you’re pregnant, speak to your midwife about any change in discharge. Visit a sexual health clinic if you have bleeding between periods or after sex, sores or blisters, or your symptoms started after sex with a new partner. Online treatment is not suitable in these situations.
Key fact: Two rules do most of the work — take every dose with food, and no alcohol until 48 hours after the last one.
Get BV Treatment Online
Access Doctor’s GPhC-registered pharmacist independent prescribers assess BV symptoms online and, where treatment is suitable, supply it from our UK pharmacy. Approved before 3pm, Monday to Friday? Dispatched the same day in plain packaging, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start BV Consultation →Adults only online, and not in pregnancy or breastfeeding. Access Doctor’s online BV service is for adults aged 18 and over who aren’t pregnant or breastfeeding. If that isn’t you, your GP, midwife or a local sexual health clinic can assess and treat BV free of charge. Under 18? NHS sexual health clinics see young people confidentially.
Dosage for BV
The usual UK dose for bacterial vaginosis is metronidazole 400mg twice a day for 7 days, which is 14 tablets. That’s the dose in the product licence, it’s the NICE CKS first-line option, and it’s the course Access Doctor supplies. Some guidance allows a shorter course, so always follow the dose on your label.
400mg
Standard dose per tablet
Twice daily
Roughly 12 hours apart
7 days
The course we supply (14 tablets)
A single 2g dose exists as an alternative and is occasionally used where adherence to a week-long course is unlikely. BV comes back sooner after it, so it is not routinely recommended in UK practice, and Access Doctor only supplies the 7-day course. Extended courses of ten to fourteen days are sometimes used for recurrent BV.
Always follow the regimen on your own label. Doses differ between conditions — a dental infection and a course of BV treatment are not the same prescription. If your label differs from what is described here, follow the label and ask your pharmacist if you are unsure.
How and when to take each dose
1
Take it with or after food
This is the single most useful thing you can do to reduce nausea. Metronidazole on an empty stomach is noticeably harder to tolerate, and nausea is a common reason people stop early.
2
Swallow whole with a full glass of water
Do not crush or chew the tablets — they are extremely bitter. Stay well hydrated across the course.
3
Space doses about twelve hours apart
Pick two anchors around meals and keep to them — 8am with breakfast and 8pm with dinner works for most people. Even spacing keeps drug levels steadier.
4
Set a reminder for the whole course
A repeating phone alarm for the full 7 days is a small effort that prevents the most common cause of treatment failure — missed and forgotten doses.
The alcohol rule in full
This is the rule people most want to negotiate. We get it: a week is a long time if there’s a birthday in the middle. So here it is properly.
Do not drink alcohol during your metronidazole course, or for 48 hours after your final dose. The reaction can include facial flushing, a throbbing headache, severe nausea, vomiting, abdominal cramps and a racing heartbeat. It is not dangerous in most healthy people, but it is genuinely unpleasant and can be frightening.
Why it happens
Metronidazole interferes with the enzyme that breaks down acetaldehyde, an intermediate product of alcohol metabolism. Acetaldehyde accumulates, and it is the accumulation that produces the symptoms — the same mechanism deliberately exploited by disulfiram, the medicine used to deter drinking in alcohol dependence.
The hidden sources
Alcohol appears in more places than the obvious ones, and these catch people out mid-course.
- Some cough and cold liquid medicines contain alcohol — check the label before taking one.
- Mouthwashes frequently contain alcohol; use an alcohol-free version during the course.
- Some tonics and herbal preparations are alcohol-based.
- Low-alcohol beers and wines still contain alcohol; alcohol-free versions labelled 0.0% are the safer choice.
- Alcohol used in cooking largely evaporates, but dishes with substantial uncooked alcohol are best avoided.
What to do if you have already had a drink
Do not panic and do not stop the antibiotic. Stop drinking, drink water, and wait it out — symptoms usually settle within a few hours. Continue the course as prescribed. Seek medical advice if you have chest pain, severe or persistent vomiting, or feel very unwell.
If a week without alcohol is genuinely impractical — a wedding, a holiday already booked — say so rather than skipping doses. Dalacin 2% cream contains clindamycin and carries no alcohol restriction. It’s currently out of stock with us, but your GP or a sexual health clinic can prescribe it.
Missed doses
Missing an occasional dose is common and easily handled.
| Situation | What to do |
|---|---|
| Remembered within a few hours | Take it now, then continue as normal |
| Next dose nearly due | Skip the missed dose and take the next one at the usual time |
| Missed a whole day | Resume the normal schedule — do not double up. Mention it if symptoms have not settled by the end of the course |
| Vomited within an hour of a dose | Take a replacement dose if you can keep it down; contact your pharmacist if vomiting continues |
| Vomited more than an hour after | The dose has most likely been absorbed — do not repeat it |
Never take two doses together to make up for a missed one. Doubling up increases side effects without improving the outcome.
Finishing the course
Most women feel substantially better by day two or three, with several days of tablets still to take. Finishing anyway is important.
Symptoms resolve when the anaerobic overgrowth drops below the threshold that produces noticeable odour and discharge — which happens well before the population has been reduced as far as the course is designed to reduce it. Stopping at that point leaves a larger surviving reservoir, and that reservoir regrows faster.
Our guide to how long BV takes to clear up sets out the expected timeline day by day, including what genuinely counts as treatment not working.
Taking it with other medicines
Paracetamol and ibuprofen are fine alongside metronidazole. A small number of medicines are not, and these should be declared at consultation.
Warfarin
Metronidazole enhances its effect and increases bleeding risk. INR monitoring is usually required.
Lithium
Levels can rise, risking toxicity. Monitoring or an alternative antibiotic may be needed.
Phenytoin and phenobarbital
Levels can be affected, which may alter seizure control. Specialist advice needed.
Disulfiram
Should not be taken within two weeks of metronidazole — the combination can cause confusion and psychotic reactions.
The full interaction list and the complete side effect picture are in metronidazole side effects and warnings.
If you are using the vaginal gel instead
Zidoval delivers the same antibiotic locally. The dosing is different — one applicator at bedtime for five nights rather than tablets twice daily — and very little reaches the bloodstream. The Zidoval leaflet says a reaction with alcohol is unlikely but can’t be ruled out, so it’s sensible to avoid alcohol during the course and for 48 hours afterwards. The leaflet also advises against using the gel during your period or having sex during treatment.
Avoid tampons during a gel course, as they can soak up the gel. Step-by-step application is covered in Zidoval vaginal gel for BV: how to use it, and the two routes are compared in BV treatment options compared.
Get BV Treatment Online
Complete a short online consultation and our GPhC-registered pharmacist independent prescribers will check suitability before dispensing. Approved before 3pm, Monday to Friday? Dispatched the same day in plain packaging, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start BV Consultation →UK safety and getting treatment
Every antibiotic treatment for BV in the UK, whether tablets, gel or cream, is a prescription-only medicine. 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, and don’t keep leftover tablets for next time: return unused medicine 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.
You can get BV treatment free from your GP or a sexual health clinic, and many clinics offer walk-in appointments and STI testing at the same visit. Our private online service is an alternative for adults aged 18 and over who aren’t pregnant or breastfeeding. You can see all our BV treatment online options on one page.
Frequently Asked Questions
What is the dose of metronidazole for BV?
The usual UK dose is metronidazole 400mg twice a day, about 12 hours apart, for 7 days, which is 14 tablets. A single 2g dose is sometimes used, but BV comes back sooner after it, so it isn’t routinely recommended and Access Doctor doesn’t supply it.
How long after metronidazole can I drink alcohol?
Wait at least 48 hours after your final dose. Alcohol must also be avoided throughout the course. Drinking too soon can cause flushing, a throbbing headache, severe nausea, vomiting and palpitations.
Should metronidazole be taken with food?
Yes. Take each dose with or immediately after a meal and swallow the tablet whole with a full glass of water. Taking it on an empty stomach makes nausea considerably more likely.
What should I do if I miss a dose of metronidazole?
Take it as soon as you remember, unless your next dose is nearly due — in which case skip the missed one and carry on as normal. Never take two doses together to make up for a missed dose.
Can I stop metronidazole early if my symptoms have gone?
No. Symptoms settle before the bacterial overgrowth is fully suppressed, so stopping early leaves a larger surviving population and makes early recurrence more likely. Finish every dose in the course.
Does the alcohol rule apply to Zidoval vaginal gel?
To be safe, yes. Very little metronidazole is absorbed from the gel, so the product information says a reaction is unlikely, but it can’t be ruled out. Avoid alcohol during the five-night course and for 48 hours after the last application.
Can I take painkillers with metronidazole?
Paracetamol and ibuprofen can be taken alongside metronidazole. Check the label of any liquid medicine, though, as some cough and cold preparations contain alcohol, which should be avoided during the course.
How many hours apart should I take metronidazole twice a day?
About 12 hours apart, for example 8am with breakfast and 8pm with your evening meal. It doesn’t need to be exact to the minute, so a little either way to fit your meals is fine. What matters most is taking both doses every day for the full 7 days.
Completing the treatment
Metronidazole tablets are available from Access Doctor after an online consultation with a pharmacist independent prescriber. If the alcohol restriction is the sticking point, clindamycin cream is the alternative without one. It’s currently out of stock with us, so ask your GP or a sexual health clinic.
Bacterial vaginosis · Rx
Metronidazole 400mg Tablets
The usual first-choice BV treatment: one tablet twice a day for 7 days, after an online consultation.
View →Bacterial vaginosis
BV Treatment Online
All our BV options in one place, including when to see your GP or a sexual health clinic instead.
View →References
- National Institute for Health and Care Excellence. Clinical Knowledge Summaries: Bacterial vaginosis. 2025. cks.nice.org.uk
- British National Formulary. Metronidazole. bnf.nice.org.uk
- Electronic Medicines Compendium. Metronidazole 400mg Tablets — Summary of Product Characteristics. medicines.org.uk
- NHS. Metronidazole: how and when to take it. nhs.uk
- Electronic Medicines Compendium. Zidoval 7.5mg/g Vaginal Gel — 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.