How to Take Metronidazole: Dosage, Timing and Alcohol

Part of the Access Doctor Bacterial Vaginosis guide. New to this medicine? See what metronidazole is and what it treats.

Dosage and How to Take It

The dose and length of a metronidazole course depend on the infection being treated — your prescriber will set the exact regimen. These are the usual adult doses:

• Swallow tablets whole with a glass of water — do not chew
• Take them with or after food to reduce the chance of nausea
• Space your doses evenly through the day to keep steady levels in the body
• Finish the whole course, even once you feel better, to fully clear the infection
• Doses for children are worked out by age or weight — never use adult dosing for a child

Metronidazole and Alcohol

Do not drink any alcohol while taking metronidazole, or for at least 48 hours after your final dose. This is one of the most important rules with this medicine — it is not a minor caution.

Combining the two causes a disulfiram-like reaction (sometimes called the "antabuse effect"). Metronidazole blocks the enzyme that breaks down acetaldehyde, a toxic by-product of alcohol, so acetaldehyde builds up and causes:

• Nausea and vomiting (metronidazole can already cause nausea — alcohol makes it much worse)
• Stomach pain and cramps
• Hot flushes and sweating
• A pounding heartbeat (palpitations)
• Headache and dizziness

When Will I Feel Better?

Metronidazole works quickly. For bacterial vaginosis, symptoms often improve within 2–3 days, though you should still finish the 5–7 day course. More complex infections (such as a dental abscess with swelling) can take longer to settle. If you are not improving after finishing the course, or symptoms worsen, contact your prescriber.

Food and Driving

Food: take metronidazole with or after food to minimise stomach upset. Beyond avoiding alcohol, there are no special dietary restrictions.

Driving: metronidazole does not usually affect driving or cycling. Very rarely it can cause drowsiness or blurred vision — if that happens, do not drive or operate machinery until you are fully alert and your vision is clear.

If You Miss a Dose

Take the missed dose as soon as you remember — unless it is almost time for your next one, in which case skip it and carry on as normal. Never take a double dose to make up for a missed one. A daily phone alarm helps you stay on schedule through the course.

Interactions With Other Medicines

Tell your prescriber about every medicine you take — including over-the-counter products, herbal remedies and vitamins — before starting metronidazole. Key interactions include:

• Warfarin (blood thinner) — metronidazole can increase its effect, raising bleeding risk
• Lithium — metronidazole can raise lithium levels, risking toxicity
• Disulfiram (Antabuse) — combining can cause severe reactions; avoid
• Some antidepressants and anti-epileptics — declare these during your consultation

Pregnancy and Breastfeeding

Use in pregnancy and breastfeeding should be discussed with your prescriber. Metronidazole is generally avoided in the first trimester unless necessary, though it may be prescribed for infections like BV where the benefit outweighs the risk. It passes into breast milk, so breastfeeding is usually not recommended during treatment and for a period after. Your prescriber will advise for your situation.

Side Effects (Brief)

The most common side effects are a metallic taste, nausea, loss of appetite, diarrhoea and headache — usually mild. For the full list, how long they last, and the rare-but-serious signs to watch for, see our dedicated guide: metronidazole side effects and what to do about them.