The most common side effects of metronidazole are nausea, diarrhea, abdominal pain, headache, skin reactions, photosensitivity, and anemia. These symptoms usually go away after stopping the medication but may be cause for concern if they do not. Your risk of developing these side effects will be higher if you have a history of any of the following: bone marrow problems, liver disease, kidney disease, heart disease, seizure disorder, stroke, tuberculosis, viral infection, or immune system problem. Rare but serious side effects include irritability, depression, anxiety, confusion, hallucinations, sudden mood changes, trouble sleeping, loss of appetite, weight loss, dry mouth, tingling hands and feet, blue-black colored urine, lightening of the skin, and eyes. If you experience any of these symptoms, call your doctor immediately.