What are the Side Effects of Metronidazole

ANTIBIOTICS & INFECTIONS Sep 26, 2025
Metronidazole is an antibiotic commonly used to treat anaerobic bacterial infections, protozoan infections, Crohn’s disease, and Helicobacter-associated gastritis. It works by targeting and destroying the germs responsible for the infection. Available in various forms, such as tablets and gels, Metronidazole comes with different side effects depending on its form. Below, we outline the common, serious, and rare side effects associated with this medication.

White round tablets in a transparent medicine bottle close-up

Side Effects of Metronidazole Tablets:

Gastrointestinal Issues
When taken orally as tablets, Metronidazole is generally well-tolerated. However, gastrointestinal side effects are common, including nausea, which may be accompanied by anorexia, headache, diarrhea, vomiting, constipation, abdominal cramping, oral mucositis, taste disorders, and epigastric pain. A metallic or unpleasant taste is not normal and should be reported. Crohn’s disease patients are at higher risk for developing certain extraintestinal cancers. Pancreatitis is also a possible side effect, but it usually resolves after stopping the medication. If alcohol is consumed during treatment, patients may experience flushing, nausea, headache, vomiting, or abdominal distress.

Patients may also notice glossitis, tongue discoloration, stomatitis, or a furry tongue, which could be due to Candida overgrowth during effective treatment.

Unwell person resting with medication bottle nearby

Body as a Whole
Metronidazole may cause hypersensitivity reactions like urticaria, angioedema, pruritus, rash, fever, and anaphylactic shock. Dryness of the mouth and nasal congestion are other potential side effects. It can also cause mild erythematous eruptions and fleeting joint pain. In rare cases, more serious conditions such as toxic epidermal necrolysis and Stevens-Johnson syndrome may develop.

Central Nervous System (CNS) Disorders
CNS-related side effects are a concern with Metronidazole and include convulsive seizures, vertigo, headache, dizziness, and incoordination. Confusion and hallucinations have also been reported. Other symptoms include insomnia, depression, weakness, irritability, ataxia, tremor, gait impairment, nystagmus, and dysarthria. These side effects may resolve once the medication is discontinued.

Hepatic Issues
Metronidazole increases the risk of developing cholestatic or mixed hepatitis, liver injury, and elevated liver enzymes. Cases of liver failure have been reported, especially when taken in combination with other antibiotics.

Eye Disorders
Eye-related side effects, including myopia, decreased visual acuity, changes in color vision, and diplopia, have been noted in some patients.

Genitourinary Tract Issues
Metronidazole use may cause dryness of the vagina, cystitis, pruritus, pelvic pressure, and dysuria. Rare side effects include polyuria, proctitis, pyuria, fever, incontinence, dyspareunia, and decreased libido. Candida proliferation in the vagina may also occur.

Haematologic Disorders
Leucopenia is a potential side effect, as well as rare occurrences of bone marrow depression. Other risks include neutropenia, agranulocytosis, or thrombocytopenia.

Ear Disorders
Some patients have reported ear-related issues, including tinnitus, impaired hearing, or hearing loss.

Graph and medical explanation of Metronidazole side effects

If any of these side effects become bothersome or troubling, it is important to contact your healthcare specialist for advice and further management.
What are the Side Effects of Metronidazole - ZARVY Blog