What Is Metronidazole and What Is It Used For?

Part of the Access Doctor Bacterial Vaginosis guide.

What Is Metronidazole?

Metronidazole is a potent antibiotic used to treat a variety of bacterial and parasitic infections. It belongs to a class of medicines called nitroimidazoles. It is available only with a prescription, which can be obtained following a consultation with a qualified healthcare professional — including via Access Doctor’s GPhC-regulated online consultation service. Metronidazole comes in several forms — tablets, a topical gel (such as Zidoval), and a cream — making it a versatile treatment across a broad range of infections.

What Does Metronidazole Treat?

Metronidazole targets anaerobic bacteria and protozoa — organisms that thrive in environments with little to no oxygen. This makes it effective across a wide spectrum of infections:

How Does Metronidazole Work?

Once inside a bacterial or parasitic cell, metronidazole is chemically reduced by anaerobic organisms — creating unstable, reactive intermediate compounds. These compounds damage the organism’s DNA, disrupting essential cellular functions and causing cell death.

This mechanism makes metronidazole particularly effective against anaerobic pathogens and certain protozoa, distinguishing it from many other antibiotics that require oxygen-dependent processes. It acts as both an antibacterial and an antiparasitic agent — hence its wide range of clinical uses.

Key Facts About Metronidazole

• Avoid alcohol during treatment and for at least 48 hours after. Combining metronidazole with alcohol can trigger a disulfiram-like reaction — see how to take metronidazole (dosage & alcohol).
• Common side effects include nausea, a metallic taste, diarrhoea, and occasionally headache or dizziness — see the full metronidazole side effects guide.
• Treatment length varies by condition — from a single dose for some infections to several weeks for rosacea.
• Complete the full course — always finish it even if symptoms improve, to prevent recurrence and resistance.

Dosage Overview

The dose and duration depend on the infection being treated. This is a general overview — for detailed dosing, timing and the alcohol interaction, see our dedicated guide on how to take metronidazole.

Tablets should be swallowed whole with a glass of water, preferably after eating to minimise stomach upset. Always follow the dose and duration your clinician prescribes.

Interactions With Other Medications

Always tell your prescriber about every medicine you take — including over-the-counter products, herbal supplements and vitamins. Key interactions include warfarin (increased bleeding risk), lithium (elevated blood levels), disulfiram, 5-fluorouracil, and ciclosporin. The full interactions detail is in our metronidazole side effects and interactions guide.

Pregnancy and Breastfeeding

Use during pregnancy and breastfeeding should be discussed with your prescriber. Metronidazole is sometimes used in pregnancy — particularly for BV, where untreated infection carries its own risks — but is generally avoided in the first trimester unless necessary. It passes into breast milk, so breastfeeding is typically not recommended during treatment and for a period after. Your prescriber will advise based on your circumstances.

Antibiotic Resistance

Overuse or misuse of antibiotics drives resistance — one of the biggest global health challenges today. To minimise the risk: only take metronidazole when prescribed; complete the full course even if you feel better; and never share your medication or self-medicate with leftover antibiotics.