metronidazole
Brand names: Flagyl
Metronidazole is an antibiotic medicine. It fights bacteria and certain parasites in your body.
Drug Shortage Alert
metronidazole is currently listed as in shortage by the FDA. Affected manufacturer: InfoRLife SA. Status: Limited Availability.
View all drug shortages →Drug Pricing (NADAC)
Generic Price
$0.25/unit
Generic Available
Yes (35 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Metronidazole treats infections like trichomoniasis, amebiasis, and certain anaerobic bacterial infections.
Common side effects
Nausea, Headache, Loss of appetite
Key warnings
Metronidazole can cause cancer in mice and rats.
How It Works
Metronidazole works by entering the bacteria or parasite and damaging its DNA. This damage stops the bacteria or parasite from growing and multiplying. Eventually, the infection is cleared.
How to Take It
Take metronidazole exactly as your doctor tells you. For trichomoniasis, you may take a single dose or a 7-day course. For amebiasis, you will likely take it three times a day for 5 to 10 days. If you have liver problems, your doctor may lower your dose by 50%.
Pregnancy & Breastfeeding
Do not take metronidazole during the first three months of pregnancy. Talk to your doctor if you are pregnant or breastfeeding before taking this medicine.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule.
Storage
Store metronidazole at room temperature, away from moisture and heat.
Side Effects (from patient reports)
Based on 36,964 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 63,731 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 1999–2025.
Total Reports
63,731
Death-Related Reports
6,727
Hospitalization Reports
26,693
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DRUG INEFFECTIVE | 5,470 |
| 2 | NAUSEA | 4,693 |
| 3 | DIARRHOEA | 4,116 |
| 4 | OFF LABEL USE | 4,054 |
| 5 | VOMITING | 3,283 |
| 6 | PYREXIA | 3,224 |
| 7 | DRUG HYPERSENSITIVITY | 3,138 |
| 8 | PAIN | 3,129 |
| 9 | ABDOMINAL PAIN | 2,980 |
| 10 | HEADACHE | 2,882 |
| 11 | FATIGUE | 2,876 |
| 12 | DYSPNOEA | 2,238 |
| 13 | DIZZINESS | 2,201 |
| 14 | CONDITION AGGRAVATED | 2,107 |
| 15 | MALAISE | 2,017 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Metronidazole can cause cancer in mice and rats. Only use it for the conditions listed in this leaflet. Do not drink alcohol or use products with propylene glycol while taking this medicine, and for 3 days after.
Known Drug Interactions
albuterol, systemic and inhaled mebendazole amoxicillin medroxyprogesterone ampicillin, with or without sulbactam methylprednisolone atenolol metronidazole azithromycin metoprolol caffeine, dietary ingestion nadolol cefaclor nifedipine co-trimoxazole (trimethoprim and sulfamethoxazole) nizatidine diltiazem norfloxacin dirithromycin ofloxacin enflurane omeprazole famotidine prednisone, prednisolone felodipine ranitidine finasteride rifabutin hydrocortisone roxithromycin isoflurane Sorbitol (purgative doses do not inhibit theophylline absorption) isoniazid sucralfate isradipine terbutaline, s...
Mechanism: Metronidazole may reduce the speed at which your liver clears theophylline from your blood. This can cause the drug to reach levels that are toxic to your body.
What to do: Your doctor should monitor your theophylline levels while you are on this medication. Tell your doctor if you experience a persistent headache or feel very dizzy.
Lithium In patients stabilized on relatively high doses of lithium, short-term metronidazole therapy has been associated with elevation of serum lithium and, in a few cases, signs of lithium toxicity. Serum lithium and serum creatinine levels should be obtained several days after beginning metronidazole to detect any increase that may precede clinical symptoms of lithium intoxication.
Mechanism: Metronidazole can cause lithium to build up in your body, which may lead to lithium poisoning.
What to do: Your doctor should check your lithium and kidney levels a few days after you start metronidazole to ensure they stay in a safe range.
Drug Interactions Disulfiram Psychotic reactions have been reported in alcoholic patients who are using metronidazole and disulfiram concurrently. Metronidazole should not be given to patients who have taken disulfiram within the last two weeks (see CONTRAINDICATIONS ).
Mechanism: Combining these two medicines can cause serious mental health problems, such as confusion or psychotic reactions.
What to do: Do not take metronidazole if you have taken disulfiram within the last two weeks.
Drugs that Inhibit CYP450 Enzymes The simultaneous administration of drugs that decrease microsomal liver enzyme activity, such as cimetidine, may prolong the half-life and decrease plasma clearance of metronidazole.
Mechanism: Cimetidine slows down how fast your liver breaks down metronidazole, which causes the medicine to stay in your body longer.
What to do: Your doctor may need to monitor you more closely for side effects since the drug will leave your system more slowly.
Drugs that Induce CYP450 Enzymes The simultaneous administration of drugs that induce microsomal liver enzymes, such as phenytoin or phenobarbital, may accelerate the elimination of metronidazole, resulting in reduced plasma levels; impaired clearance of phenytoin has also been reported.
Mechanism: Phenytoin makes your liver clear metronidazole out of your body too quickly, while metronidazole can cause phenytoin to build up to unsafe levels.
What to do: Your doctor should monitor your blood levels closely because both medications may need dosage adjustments to work safely and effectively.
Common Questions
Can I drink alcohol while taking metronidazole?
What should I do if I experience numbness or tingling in my extremities?
Can metronidazole affect my liver?
Does metronidazole interact with other medications?
Can metronidazole cause a yeast infection?
How long does it take for metronidazole to start working?
What if my symptoms get worse while taking metronidazole?
Can metronidazole cause my urine to change color?
Is it safe to take metronidazole if I have kidney problems?
What if I am allergic to metronidazole?
What are the common side effects of metronidazole?
Does metronidazole interact with other medications?
What drug class is metronidazole?
Is metronidazole safe during pregnancy?
Is metronidazole currently in shortage?
Related Medications in Nitroimidazole Antibiotic
Other drugs grouped near metronidazole — same-class peers and common alternatives.
amikacin
Amikin
Amikacin is an antibiotic medicine.
Compare with metronidazole →
amoxicillin
Amoxil
Amoxicillin and Clavulanate Potassium is a combination medicine used to fight bacterial infections.
Compare with metronidazole →
amoxicillin/clavulanate
Augmentin
Augmentin is a combination of two medicines, amoxicillin and clavulanate.
Compare with metronidazole →
ampicillin/sulbactam
Unasyn
Unasyn is a combination of two antibiotics that fights bacteria in your body.
Compare with metronidazole →
azithromycin
Zithromax, Z-Pack
Azithromycin is an antibiotic that fights bacteria.
Compare with metronidazole →
Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
Why some drugs demand precise dosing and monitoring
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Related Health & Safety Data
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What the FDA Data Shows for metronidazole
The FDA label for metronidazole (sold under brand names such as Flagyl) classifies it as a prescription-only medication in the Nitroimidazole Antibiotic class. Metronidazole treats infections like trichomoniasis, amebiasis, and certain anaerobic bacterial infections. Official labeling lists 8 commonly reported side effects, including Nausea, Headache, Loss of appetite.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 36,964 voluntary reports. The database also lists 10 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated major severity. NADAC pricing from CMS shows a generic unit cost of $0.25.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC). Shortage status: FDA Drug Shortages Database.
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: March 3, 2023
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages