Metronidazole 500 mg is a prescription antibiotic and antiprotozoal that treats bacterial vaginosis, trichomoniasis, certain intestinal parasites like giardia, dental infections, and other anaerobic bacterial infections. A typical course is 500 mg twice daily for 7 days, though dosing varies by condition. The one rule everyone remembers: no alcohol during treatment and for 3 days after.
Metronidazole (brand name Flagyl) has been a workhorse antibiotic since the 1960s, and it fills a niche most antibiotics can’t: it kills anaerobic bacteria (the kind that thrive without oxygen) and several parasites. Here’s the practical guide.
What metronidazole treats
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Bacterial vaginosis (BV): the most common prescription use, typically 500 mg twice daily for 7 days
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Trichomoniasis: a common, curable STI; current guidance for women is 500 mg twice daily for 7 days, and partners need treatment too or reinfection is near-certain
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Giardiasis: the “backpacker’s parasite” from contaminated water, a frequent culprit when traveler’s diarrhea drags past a week
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Dental and gum infections: anaerobes dominate the mouth, so dentists reach for metronidazole often, sometimes paired with amoxicillin
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Intra-abdominal and other anaerobic infections: usually in combination with other antibiotics under closer medical supervision
Notice what’s not on the list: colds, flu, standard UTIs, most skin infections. Metronidazole is a specialist, and using it against the wrong organism does nothing but generate side effects.
How to take it
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Detail |
Typical adult use |
|---|---|
|
Common dose |
500 mg tablet, twice daily (varies by condition) |
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Typical course |
7 days for BV and trichomoniasis; giardia often shorter |
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With food? |
Optional, but food reduces the nausea |
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Missed dose |
Take when remembered unless the next is close; never double |
Finish the full course. Metronidazole side effects tempt people to quit early more than most antibiotics, and partial treatment invites relapse.
The alcohol rule, and why it’s real
Metronidazole combined with alcohol can trigger a disulfiram-like reaction: flushing, pounding headache, nausea, vomiting, and a racing heart. It’s not dangerous for most people, but it’s memorably awful. The rule covers all alcohol including cooking wine that isn’t fully cooked off and some mouthwashes, from first dose until 3 days after the last dose, since the drug clears slowly.
Side effects
The common ones: nausea (up to 12% of patients), a metallic taste that’s practically metronidazole’s signature, headache, and dark urine (harmless). Less common but worth acting on: tingling or numbness in hands or feet on longer courses (peripheral neuropathy, report it promptly), and any signs of allergic reaction. Metronidazole also interacts with warfarin (raises bleeding risk), lithium, and should never be combined with mebendazole.
Yeast infections sometimes follow a course, since metronidazole clears bacteria but not yeast; fluconazole handles that if it happens.
Getting metronidazole prescribed
Metronidazole is prescription-only in the US, and “metronidazole over the counter” searches lead either to disappointment or to gray-market sites selling unverified product. The legitimate fast path is telehealth: complete OZIO’s online health assessment, a licensed physician reviews it, and if metronidazole is the right call, metronidazole 500 mg ships from a US pharmacy. BV and trichomoniasis are among the most telehealth-treatable conditions there are, and speed matters for both comfort and transmission.
FAQ
Is metronidazole available over the counter? No. All oral metronidazole in the US requires a prescription. An online provider evaluation is the fastest legitimate route.
How long until metronidazole works? Symptom improvement usually starts within 2 to 3 days for BV and trichomoniasis. The full course still needs finishing to prevent recurrence.
Can I take metronidazole while pregnant? It’s commonly prescribed in pregnancy for BV and trichomoniasis when indicated, but that decision belongs to your OB or provider, not a blog.
Why does everything taste like metal? Metronidazole is secreted in saliva and hits bitter/metallic taste receptors. It’s harmless and resolves after the course ends. Sugar-free gum helps.
This article is for informational purposes only and is not medical advice. Metronidazole requires an evaluation by a licensed healthcare provider. If you have an STI, partner treatment and testing matter as much as your own.
