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.
Key fact: Two rules do most of the work — take every dose with food, and no alcohol until 48 hours after the last one.
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Order Metronidazole →Dosage for BV
The standard UK dose for bacterial vaginosis is metronidazole 400mg twice daily for five to seven days. This is the NICE CKS first-line recommendation and the regimen most women are given.
400mg
Standard dose per tablet
Twice daily
Roughly 12 hours apart
5–7 days
Standard course length
A single 2g dose exists as an alternative and is occasionally used where adherence to a week-long course is unlikely. It is less effective at preventing early recurrence, so it is not routinely recommended in UK practice. 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 the most common reason courses get abandoned.
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 five to seven 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, so it is worth setting out 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 at consultation rather than skipping doses. Dalacin 2% cream contains clindamycin and carries no alcohol restriction at all.
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 — but the alcohol rule still applies, because a small amount is absorbed through the vaginal wall.
Tampons must not be used during a gel course, as they absorb the product. 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.
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Order Metronidazole →Frequently Asked Questions
What is the dose of metronidazole for BV?
The standard UK dose is metronidazole 400mg twice daily for five to seven days. A single 2g dose is an alternative in some circumstances but is less effective at preventing early recurrence and is not routinely recommended.
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?
Yes. A small amount of metronidazole is absorbed through the vaginal wall, which is enough for the interaction to apply. 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.
Completing the treatment
Metronidazole is available from Access Doctor following an online consultation with a pharmacist independent prescriber. If the alcohol restriction is the sticking point, tell us — Dalacin cream is the alternative without one.
Bacterial vaginosis · Rx
Metronidazole 400mg Tablets
First-line oral antibiotic for BV, taken twice daily for five to seven days.
View product →Bacterial vaginosis · Rx
Dalacin 2% Cream
Clindamycin vaginal cream — the option with no alcohol restriction.
View product →Bacterial vaginosis · Rx
Zidoval Vaginal Gel
Metronidazole 0.75% gel applied nightly for five nights.
View product →Self-test · Pharmacy
Canestest Self-Test
Checks vaginal pH at home to help distinguish BV from thrush before you treat.
View product →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.