Metronidazole — what it treats and how to use it safely

Metronidazole is an antibiotic and antiprotozoal drug used for infections caused by anaerobic bacteria and some parasites. Doctors commonly prescribe it for bacterial vaginosis, trichomoniasis, giardiasis, amebiasis, dental infections, and certain abdominal or pelvic infections. You’ll see it as tablets, topical gels or creams, and IV form in hospitals.

The medicine works by damaging the DNA of the bacteria or protozoa, which stops them from multiplying. It only works against specific organisms, so it won’t help with viral infections like the common cold or flu. That’s why a correct diagnosis matters before taking it.

How to take metronidazole

Follow the exact dose and length your prescriber gives you. Typical adult doses include a single 2 g dose or 500 mg twice daily for trichomoniasis; 500 mg twice daily for 7 days for bacterial vaginosis; and 250–750 mg three times daily for 5–7 days for some parasitic infections. Don’t stop early even if you feel better — stopping can let the infection come back.

Take pills with food to reduce nausea. If you’re using a topical gel or cream, apply only to the affected area and avoid getting it in your mouth or eyes. For IV use, that’s managed by hospital staff — don’t try to self-administer intravenously.

Side effects, interactions, and important warnings

Common side effects are nausea, metallic taste, headache, and mild stomach upset. Less common but serious effects include numbness or tingling in hands or feet (peripheral neuropathy), seizures, or severe allergic reactions. If you get a rash, difficulty breathing, or sudden numbness, stop the drug and seek emergency care.

Never drink alcohol while taking metronidazole and for 48 hours after the last dose — alcohol can cause flushing, nausea, vomiting, and fast heartbeat. Metronidazole can also increase the effects of warfarin (a blood thinner), so doctors will monitor blood tests if you take both. Tell your prescriber about all medicines, including supplements.

Pregnancy and breastfeeding: many doctors use metronidazole in pregnancy when the benefit outweighs the risk, but always discuss it with your obstetrician. Small amounts pass into breast milk; short courses are often considered acceptable, yet check with your healthcare provider before nursing while on treatment.

Storage and buying tips: store at room temperature away from moisture. Metronidazole requires a prescription in most countries — buy from licensed pharmacies only. Avoid suspicious online sellers that don’t ask for a prescription. If cost or access is a problem, ask your pharmacist about generic options or patient assistance programs.

When to call a doctor: high fever, severe stomach pain, persistent diarrhea (two or more loose stools with blood or severe cramping), new numbness, or signs of an allergic reaction. For everyday questions about dosing and interactions, your pharmacist is a good, quick resource.

Metronidazole is effective when used correctly. Stick to your prescription, avoid alcohol, and consult your clinician if anything unusual appears.