What Is Metronidazole? Uses, Dosage, and What You Need to Know in 2026

Metronidazole is one of the most prescribed antibiotics in the world. In the United States, it's most commonly known by the brand name Flagyl, though it's widely available as an affordable generic. Whether you've been prescribed it for a vaginal infection, a dental abscess, or a gut parasite, this guide covers everything you need to know about metronidazole in 2026.

What Is Metronidazole?

Metronidazole is a nitroimidazole antimicrobial agent. First FDA-approved in 1963, it has been used for over 60 years to treat bacterial and protozoal (parasitic) infections. It works by entering bacterial and protozoal cells and disrupting their DNA — killing the microorganism or preventing its reproduction.

Unlike broad-spectrum antibiotics, metronidazole is particularly effective against anaerobic organisms — bacteria and parasites that live and grow in environments without oxygen. This makes it the right tool for many infections in the gut, reproductive tract, deep tissues, and dental structures, where anaerobic organisms thrive.

What Is Metronidazole Used to Treat?

Metronidazole has an unusually broad range of approved uses:

Bacterial Vaginosis (BV): The most common use. Metronidazole (oral or vaginal gel) is one of two first-line treatments for BV, an overgrowth of anaerobic bacteria in the vagina. Affects millions of American women annually.

Trichomoniasis: A sexually transmitted infection caused by the parasite Trichomonas vaginalis. Metronidazole (typically a 2 g single dose) is the standard treatment.

Amebiasis: Infection caused by the parasite Entamoeba histolytica. Can cause intestinal illness or liver abscess.

Giardiasis: A parasitic GI infection caused by Giardia lamblia ("beaver fever"). Common after drinking contaminated water.

Clostridioides difficile (C. diff): A serious intestinal infection. Metronidazole may be used for mild cases, though oral vancomycin and fidaxomicin are now preferred per current guidelines.

Anaerobic bacterial infections: Includes skin and soft tissue infections, bone and joint infections, lung infections, brain abscess, and bloodstream infections caused by anaerobic bacteria like Bacteroides and Clostridium species.

Pelvic inflammatory disease (PID): Used as part of combination antibiotic regimens with ceftriaxone and doxycycline.

Helicobacter pylori eradication: Used as part of combination regimens (triple or quadruple therapy) to treat H. pylori, a bacterium that causes peptic ulcers.

Surgical prophylaxis: Given before colorectal, gynecological, and other surgery involving the GI tract to prevent post-operative anaerobic infections.

Rosacea (topical forms): Metrogel, Metrocream, and Metrolotion contain topical metronidazole and are used to treat inflammatory lesions of rosacea, leveraging metronidazole's anti-inflammatory properties.

What Forms Does Metronidazole Come In?

Oral tablets: 250 mg and 500 mg (most common)

Oral capsules: 375 mg

Extended-release tablets: 750 mg (Flagyl ER)

Intravenous (IV) solution: 500 mg/100 mL

Topical gel (Metrogel): 0.75% and 1%

Topical cream (Metrocream) and lotion (Metrolotion): 0.75%

Vaginal gel (Metrogel-Vaginal, Nuvessa): 0.75% and 1.3%

Typical Metronidazole Dosages by Condition

Bacterial vaginosis: 500 mg twice daily for 7 days, OR 2 g as a single dose (less preferred due to higher recurrence)

Trichomoniasis: 2 g single oral dose (both patient and partner treated simultaneously)

Amebiasis: 500–750 mg three times daily for 5–10 days

Anaerobic infections: 500 mg every 6–8 hours, orally or IV, for 7–10 days (or longer for serious infections)

Surgical prophylaxis: 15 mg/kg IV approximately 1 hour before surgery; may add 7.5 mg/kg at 6 and 12 hours after initial dose

Key Safety Rules for Metronidazole

No alcohol: Avoid alcohol during treatment and for at least 3 days after your last dose — a disulfiram-like reaction can occur.

Finish the full course: Even if symptoms improve early, complete your prescription to prevent antibiotic resistance and recurrence.

Pregnancy consideration: Generally avoided in the first trimester for trichomoniasis. Talk to your doctor if pregnant.

Report neurological symptoms immediately: Numbness, tingling, seizures, or confusion require prompt medical evaluation.

The Bottom Line

Metronidazole is a versatile, affordable antibiotic that has been treating bacterial and parasitic infections for over 60 years. For most patients, a short course of oral metronidazole is effective and well-tolerated. The most important rules to remember are: take with food to reduce nausea, don't drink alcohol, and finish the full course. Want to understand how it actually works in your body? See our deep dive on

how metronidazole works.