Side effects of metronidazole

Metronidazole is a prescription antibiotic medication used to treat amebic liver abscess, intestinal amoebiasis, trichomoniasis, bacterial vaginosis, pelvic inflammatory disease (PID) and to prevent infection after colorectal surgery.

This type of medication is ineffective against viral infections, such as colds and the flu, as are all antibiotics. The brand names for metronidazole are Flagyl, Flagyl 375 and Flagyl ER.


Metronidazole is available as a capsule, tablet and extended-release tablet. The tablet and capsule form of this medication should be taken by mouth with food. The extended-release form of this medication should be taken one hour before or two hours after meals. You should take the full prescribed dose of this medication and should not discontinue metronidazole without physician guidance.

Side Effects

Metronidazole therapy can cause side effects such as sun sensitivity leading to sunburn, vomiting, diarrhoea, loss of appetite, upset stomach, dry mouth, metallic taste in mouth, yeast infections, mouth or tongue irritation and reddish-brown or dark urine. Another side effect of metronidazole use is a "furry tongue." This is a temporary condition in which the finger-like projections on the tongue don't fall off like normal, but instead grow and produce a "furry" appearance. Contact your physician for further advice if these side effects become bothersome.

Serious Side Effects

Serious side effects of metronidazole use can include a rash, itching, stuffy nose, fever, seizures, tingling or numbness in the hands or feet, and joint pain. Contact your physician, or emergency medical services if the side effects are severe, immediately if you experience any of these side effects.


Metronidazole should not be used in conjunction with alcohol due to the potential side effects of vomiting, stomach cramps, upset stomach, headaches, flushing and sweating. You should not consume alcohol for at least three days after completing this medication. This medication interacts with certain prescription medications, so you should inform your physician of any prescription or over-the-counter medications you are taking.


Metronidazole has caused cancer in laboratory mice and rats, so this medication should be prescribed only if necessary. Your physician will weigh the risks and benefits of prescribing this medication. This medication should not be taken the first trimester of pregnancy.