Key Takeaways
- Metronidazole is a nitroimidazole antibiotic that treats anaerobic bacteria and certain protozoa.[1]
- Its most common uses are trichomoniasis and bacterial vaginosis, plus certain dental, abdominal, and parasitic infections.[2][3]
- Complete the full prescribed course, even if symptoms improve early.[1]
- Avoid alcohol during treatment and for several days after, since the combination causes a distinctly unpleasant reaction.[1]
- Common side effects include a metallic taste and nausea; long-term or high-dose use can cause nerve symptoms.[1]
Metronidazole is one of those medicines prescribed for a surprisingly wide range of infections, from a sexually transmitted parasite to a tooth infection to a stomach ulcer. It is effective and generally safe when used correctly, but it comes with one unusual rule that catches people off guard: no alcohol while you take it. This guide explains what the drug is, what it treats, and the few things you genuinely need to know while taking it.
What Is Metronidazole?
Metronidazole is a nitroimidazole antimicrobial, meaning it works against a specific set of anaerobic bacteria, organisms that thrive without oxygen, and certain protozoa, single-celled parasites.[1] It is available by mouth, as a topical gel or cream, and as a vaginal gel. It is not a broad-spectrum antibiotic like penicillin; it targets a narrower range, which is why it is chosen for specific infections.
What It Treats
| Condition | Type | Notes |
|---|---|---|
| Trichomoniasis | Sexually transmitted infection | Curable; treat partners too[2] |
| Bacterial vaginosis | Vaginal bacterial imbalance | Common cause of discharge[3] |
| Anaerobic infections | Dental, abdominal, pelvic | Infections caused by oxygen-avoiding bacteria[1] |
| Parasitic infections | Amebiasis, giardiasis | Protozoal gut infections[1] |
How It Works
Once inside an anaerobic bacterium or parasite, metronidazole is converted into a reactive form that disrupts the organism's DNA, killing it.[1] Because this conversion only happens in oxygen-poor environments, the drug spares most normal aerobic bacteria in the body.
Dosing by Condition
| Condition | Typical adult regimen |
|---|---|
| Trichomoniasis (women) | 500 mg twice daily for 7 days[2] |
| Trichomoniasis (men) | 2 g single dose[2] |
| Bacterial vaginosis | 500 mg twice daily for 7 days[3] |
| Other anaerobic infections | Varies; prescribed by a clinician[1] |
The dose depends entirely on the infection, which is why it is never a good idea to reuse a leftover course. Always finish the full course as prescribed, even after you feel better.[1]
The Alcohol Warning
The rule everyone remembers about metronidazole is real: do not drink alcohol while taking it and for at least 48 to 72 hours after the last dose.[1] Combining metronidazole with alcohol can produce a disulfiram-like reaction, flushing, nausea, vomiting, a racing heart, and a throbbing headache. It is unpleasant rather than usually life-threatening, but it is simple to avoid.
Side Effects
The most common side effects are a metallic taste in the mouth and nausea.[1] Metronidazole also commonly turns urine darker, sometimes reddish-brown, which is harmless but worth knowing so it does not alarm. With prolonged or high-dose use, a more serious side effect is peripheral neuropathy, numbness, tingling, or pain in the hands and feet.[1]
Other Interactions
| Interaction | Effect |
|---|---|
| Alcohol | Disulfiram-like reaction[1] |
| Warfarin | Raised bleeding risk, needs monitoring[1] |
| Lithium | Raised lithium levels[1] |
Tell your clinician about all medicines you take, and about any history of nerve, liver, or blood problems, before starting metronidazole.
Pregnancy and Breastfeeding
Metronidazole is used in pregnancy when indicated and is considered low risk according to available data, but any infection during pregnancy should be managed by the obstetric team rather than through general telehealth care.[2] This guide's use of metronidazole assumes a non-pregnant adult.
When to Contact a Clinician
You develop numbness, tingling, or pain in the hands or feet, severe nausea that prevents completing the course, or signs of an allergic reaction such as a rash, swelling, or difficulty breathing.[1]
Frequently Asked Questions
No. Avoid alcohol during treatment and for 48 to 72 hours after the last dose, since the combination causes flushing, nausea, vomiting, and headache.[1]
It begins working quickly, but always complete the full prescribed course, even after symptoms improve, to fully clear the infection.[1]
A metallic taste is one of the drug's most common and harmless side effects, along with nausea. It resolves after finishing the course.[1]
Yes, it can turn urine a darker, reddish-brown color. This is harmless and expected.[1]
Metronidazole is used in pregnancy when indicated and is considered low risk, but pregnancy care is managed by the obstetric team.[2]
References
- Weir CB, Le JK. Metronidazole. StatPearls. Updated 2026. PubMed PMID 30969550
- Centers for Disease Control and Prevention. STI Treatment Guidelines, 2021: Trichomoniasis. cdc.gov
- Centers for Disease Control and Prevention. STI Treatment Guidelines, 2021: Bacterial Vaginosis. cdc.gov