Metronidazole (Flagyl, Likmez) - Uses, Side Effects, and More

What are the most common side effects of metronidazole?

The most common side effects of metronidazole are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

• Nausea and vomiting
• Headache
• Loss of appetite
• Diarrhea
• Stomach pain or cramps
• Constipation
• Unpleasant metallic taste

There may be other side effects of metronidazole that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of metronidazole?

While less common, the most serious side effects of metronidazole are described below, along with what to do if they happen.

Severe Allergic Reactions. Metronidazole may cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for Drug Reaction with Eosinophilia and Systemic Symptoms. It is also sometimes called multiorgan hypersensitivity. This is a reaction that can affect multiple parts of the body, including your liver, kidneys, and heart. Stop taking the medicine and get help right away if you have any of the following symptoms of this serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching, skin rash, or pale red bumps on the skin called hives
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain
• Dark-colored urine
• Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Severe Skin Reactions. Metronidazole may cause severe skin reactions called Stevens-Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), and acute generalized exanthematous pustulosis (AGEP), which can lead to death if not treated. If you develop a rash or pus-filled pimples, stop taking metronidazole and immediately call your healthcare provider. Get emergency help right away if you have any of the following symptoms of a severe skin reaction.

• Painful red or purple skin that looks burnt and peels off
• Flat red rash or blisters on your skin, mouth, nose, and genitals
• Red, painful, watery eyes

Nerve Problems. Nerves are the fibers that carry sensations from your body to the brain. Damage to these nerves, called peripheral neuropathy (including nerves in your eyes) may happen in people who are taking metronidazole. Stop taking metronidazole and call your healthcare provider if you develop pain, burning, tingling, numbness, or weakness in your arms, hands, legs, or feet or if you develop blurred or reduced vision or pain in your eyes.

Brain or Spinal Cord Problems. Metronidazole may cause meningitis (inflammation of the protective membranes surrounding the brain and spinal cord) or a rare but potentially serious condition that affects the brain, called encephalopathy. Stop taking the medicine and get help right away if you have any of the following symptoms of encephalopathy.

• Trouble with balance or coordination
• Dizziness
• Slurred or slow speech
• Confusion, memory problems, or difficulty concentrating
• Severe headache
• Stiff neck
• Fever

Seizures. Some people who have taken metronidazole have reported having seizures. There are many different types of seizures and some of them are not easy to recognize. Stop taking metronidazole and call your healthcare provider if you have any of the following signs that a seizure is happening or could happen.

• Muscle twitching, jerking, spasms, tremors, or other uncontrolled movements
• Stiffening of your arms and legs
• Feeling anxious, nervous, confused, or a sense of dread
• Feeling dizzy or lightheaded
• Falling or losing consciousness

Inflammation of the Pancreas (Pancreatitis). Metronidazole may cause inflammation of the pancreas, which is called pancreatitis. Stop taking metronidazole and call your healthcare provider right away if you have symptoms of pancreatitis, including vomiting or severe pain in the upper part of your belly that travels to your back.

Oral Thrush or Vaginal Yeast Infections. A yeast infection may happen during or after treatment with metronidazole. This infection can be in your mouth and throat (oral thrush), or in the vaginal area (vaginal yeast infection). Metronidazole does not treat yeast infections. You may need treatment with an antifungal medicine. Contact your healthcare provider if you have any of the following symptoms.

• Cracking in the corners of the mouth
• Loss of taste
• Red or white patches in the mouth or throat
• Raised white spots in the mouth or throat
• Vaginal discharge, itching, or discomfort

Heart Rhythm Changes. Metronidazole may cause a rare dangerous heart rhythm problem called QT prolongation and torsade de pointes. Some people have a higher risk for this, including people who are older, have other people in their family who have had these conditions, have low potassium or magnesium, or who take some medicines for other heart rhythm problems. Tell your healthcare provider right away if you faint or have changes in your heart rate or rhythm such as a fast or skipped heartbeat.