Metronidazole: what it treats and how to use it safely

Metronidazole is a prescription antibiotic that fights anaerobic bacteria and some parasites. Doctors commonly use it for bacterial vaginosis, trichomoniasis, giardiasis, amebiasis, certain abscesses, and as part of H. pylori treatment. You’ll see it as pills, gel, or IV depending on how serious the infection is.

This drug works differently from penicillin-type antibiotics, so it’s chosen when those won’t help. It kills the germs that live where oxygen is low (like deep tissues or the gut) and eliminates protozoa that cause intestinal or genital infections.

Common doses and how to take it

Exact dose depends on the infection. Typical adult examples you may hear about:

- Trichomoniasis: 2 g single oral dose or 500 mg twice daily for 7 days.
- Bacterial vaginosis: 500 mg twice daily for 7 days or a single 2 g dose.
- Giardiasis: 250–500 mg three times daily for 5–7 days.
- Severe anaerobic infections (IV): 500 mg every 8 hours, switched to oral when stable.

Take oral metronidazole with food to cut down on stomach upset. Finish the full course even if you feel better early—stopping can let the infection come back. Don’t split or crush extended-release forms unless your pharmacist says it’s okay.

Side effects, interactions, and safety tips

Common side effects are nausea, metallic taste, headache, and mild stomach upset. Less common but serious: seizures, severe allergic reactions, or signs of liver trouble (yellowing skin, dark urine). If you notice worrying symptoms, contact your provider right away.

Avoid alcohol while taking metronidazole and for 48 hours after finishing the pills. Drinking alcohol can cause flushing, nausea, vomiting, and fast heartbeat. Also watch for drug interactions: metronidazole can increase warfarin effects (higher bleeding risk) and interact with certain diabetes meds and other antibiotics. Tell your doctor about all medicines and supplements you take.

Pregnancy and breastfeeding: talk with your clinician. In some cases metronidazole is used during pregnancy, but decisions depend on the situation. If you are breastfeeding, ask about timing or alternatives so the infant’s safety is considered.

Other quick tips: don’t share your prescription, store tablets in a cool dry place, and use a licensed pharmacy if ordering online—always keep a valid prescription. If symptoms persist after treatment or return, see your provider for testing and possible alternative care.