Metronidazole Side Effects

Medically reviewed by Drugs.com. Last updated on Jul 25, 2024.

Applies to metronidazole: intravenous solution.

Other dosage forms:

• oral capsule, oral powder for suspension, oral tablet

Important warnings This medicine can cause some serious health issues

Intravenous route (solution)

Metronidazole has been shown to be carcinogenic in mice and rats.

Its use, therefore, should be reserved only for conditions for which it is approved.

Serious side effects of metronidazole

Along with its needed effects, metronidazole may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur while taking metronidazole:

More common side effects

• agitation
• back pain
• blindness
• blurred vision
• burning, crawling, itching, numbness, pain, prickling, "pins and needles", or tingling feelings
• change in taste
• clay-colored stools
• confusion
• dark-colored urine
• decreased vision
• dizziness
• drowsiness
• eye pain
• fever
• headache
• irritability
• itching of the vagina or outside genitals
• light-colored stools
• loss of appetite
• loss of taste
• mood or mental changes
• nausea
• pain during sexual intercourse
• seeing or hearing things that are not there
• seizures
• stiff neck or back
• stomach pain
• thick, white curd-like vaginal discharge without odor or with mild odor
• uncontrolled eye movements
• unpleasant breath odor
• unsteadiness or awkwardness
• unusual tiredness or weakness
• vomiting
• vomiting of blood
• weakness in the arms, hands, legs, or feet
• yellow eyes or skin

Incidence not known

• black, tarry stools
• blistering, peeling, or loosening of the skin
• changes in skin color
• changes in speech patterns
• chest pain
• chills
• cough
• diarrhea
• fainting
• fast, pounding, or irregular heartbeat or pulse
• feeling of warmth
• itching
• joint or muscle pain
• lower back or side pain
• pain, tenderness, or swelling of the foot or leg
• painful or difficult urination
• pale skin
• red skin lesions, often with a purple center
• red, irritated eyes
• redness of the face, neck, arms, and occasionally, upper chest
• shakiness and unsteady walk
• slurred speech
• sore throat
• sores, ulcers, or white spots in the mouth or on the lips
• trouble with speaking
• unsteadiness, trembling, or other problems with muscle control or coordination
• unusual bleeding or bruising

Other side effects of metronidazole

Some side effects of metronidazole may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

• dry mouth
• hives or welts, skin rash
• redness of the skin
• stomach discomfort
• stuffy nose
• unpleasant metallic taste

For healthcare professionals

Applies to metronidazole: compounding powder, intravenous powder for injection, intravenous solution, oral capsule, oral suspension, oral tablet, oral tablet extended release.

General adverse events

The most serious side effects reported were convulsive seizures, encephalopathy, aseptic meningitis, optic neuropathy, and peripheral neuropathy (characterized by numbness/paresthesia of an extremity).^[Ref]

Nervous system

• Very common (10% or more): Headache (up to 18%)
• Common (1% to 10%): Dysgeusia/taste perversion (e.g., metallic taste, sharp unpleasant metallic taste, taste of alcoholic beverages modified), dizziness
• Rare (0.01% to 0.1%): Encephalopathy (e.g., confusion, fever, headache, hallucinations, paralysis, light sensitivity, disturbances in sight and movement, stiff neck), aseptic meningitis, seizure, somnolence, peripheral neuropathy, ataxia
• Very rare (less than 0.01%): Subacute cerebellar syndrome (e.g., ataxia, dysarthria, gait impaired, nystagmus, tremor), drowsiness, convulsions, incoordination
• Frequency not reported: Dysarthria, hypoesthesia, paresthesia, peripheral sensory neuropathy, transient epileptiform seizures, hearing impaired/hearing loss (including sensorineural), tinnitus, taste disorders/unpleasant taste in mouth, nystagmus, convulsive seizure, numbness, syncope, vertigo, paralysis^[Ref]

Gastrointestinal

• Very common (10% or more): Nausea (up to 10%)
• Common (1% to 10%): Abdominal pain, diarrhea, dry mouth, stomatitis, glossitis
• Rare (0.01% to 0.1%): Pancreatitis, upper abdominal pain/epigastralgia, vomiting
• Frequency not reported: Constipation, tongue discoloration, oral mucositis, furry/furred tongue, gastrointestinal disturbances (e.g., epigastric pain/distress), proctitis, sudden overgrowth of Candida in mouth, abdominal cramping, dyspepsia, pseudomembranous colitis, mucositis^[Ref]

Genitourinary

• Very common (10% or more): Vaginitis (up to 15%)
• Common (1% to 10%): Genital pruritus, abnormal urine, dysmenorrhea, moniliasis, urinary tract infection
• Rare (0.01% to 0.1%): Chromaturia
• Very rare (less than 0.01%): Darkened urine
• Frequency not reported: Vaginal dryness, vulva dryness, dysuria, vaginal candidiasis, dyspareunia, polyuria, incontinence, cystitis, pyuria, proliferation of Candida in vagina^[Ref]

Other

• Common (1% to 10%): Bacterial infection, influenza-like symptoms
• Uncommon (0.1% to 1%): Asthenia
• Rare (0.01% to 0.1%): Mucosal inflammation, pyrexia/fever
• Very rare (less than 0.01%): Flushing
• Frequency not reported: Malaise, face edema, peripheral edema, chest pain, chills, overgrowth of Candida, disulfiram-like reaction, weakness, sensation of pelvic pressure^[Ref]

Respiratory

• Common (1% to 10%): Upper respiratory tract infection, rhinitis, sinusitis, pharyngitis
• Frequency not reported: Dyspnea, nasal congestion, hiccup^[Ref]

Musculoskeletal

• Common (1% to 10%): Myalgia
• Very rare (less than 0.01%): Arthralgia
• Frequency not reported: Muscle spasms, fleeting joint pain, stiff neck^[Ref]

Hematologic

• Uncommon (0.1% to 1%): Leukopenia
• Rare (0.01% to 0.1%): Neutropenia, thrombocytopenia, pancytopenia, agranulocytosis
• Frequency not reported: Eosinophilia, bone marrow aplasia, bone marrow depression, blood dyscrasia^[Ref]

Dermatologic

• Rare (0.01% to 0.1%): Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema, erythema multiforme
• Very rare (less than 0.01%): Skin rash, pustular eruptions, acute generalized exanthematous pustulosis, pruritus
• Frequency not reported: Fixed drug eruption, swelling face, urticaria, hyperhidrosis, erythema, drug reaction with eosinophilia and systemic symptoms (DRESS), erythematosus rash, mild erythematous eruptions, pustulosis^[Ref]

Hepatic

• Rare (0.01% to 0.1%): Cholestatic hepatitis
• Very rare (less than 0.01%): Increased liver enzymes (AST, ALT, alkaline phosphatase), cholestatic/mixed hepatitis, hepatocellular liver injury, jaundice, liver failure requiring liver transplant, abnormal liver function tests
• Frequency not reported: Increased liver enzyme, hepatotoxicity/liver failure in patients with Cockayne syndrome, drug-induced hepatitis^[Ref]

Hypersensitivity

• Rare (0.01% to 0.1%): Anaphylaxis, anaphylactic shock, Jarisch-Herxheimer reaction
• Frequency not reported: Serum sickness-like reaction, immediate/delayed hypersensitivity reactions, anaphylactic reaction, hypersensitivity

Psychiatric

• Rare (0.01% to 0.1%): Hallucinations
• Very rare (less than 0.01%): Confusion/confusional state, psychotic disorders
• Frequency not reported: Depression, insomnia, depressed mood, decreased libido, irritability, psychosis, disorientation, psychotic reaction^[Ref]

Ocular

• Rare (0.01% to 0.1%): Optic neuropathy, diplopia, myopia
• Very rare (less than 0.01%): Vision disorders (e.g., diplopia, myopia)
• Frequency not reported: Optic neuropathy/neuritis, saccadic eye movement, blurred vision, decreased visual acuity, changed color vision, light sensitivity^[Ref]

Cardiovascular

• Frequency not reported: Flattening of T-wave on ECG, tachycardia, palpitations, QT interval prolonged on ECG^[Ref]

Metabolic

• Frequency not reported: Anorexia, decreased appetite^[Ref]

Oncologic

• Frequency not reported: Breast cancer, colon cancer, gastrointestinal cancer, certain extraintestinal cancers^[Ref]

An increased incidence of gastrointestinal and certain extraintestinal cancers have been reported in patients with Crohn's disease. Breast and colon cancer have been reported in medical literature in Crohn's disease patient treated with high doses of this drug for a prolonged duration; causality was not established.^[Ref]

Local

• Frequency not reported: Injection site reaction, thrombophlebitis^[Ref]

Frequently asked questions

• What happens if you drink alcohol with metronidazole?
• How long does it take for metronidazole to work?
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Further information

Metronidazole side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Medical Disclaimer