Nausea, headache may occur. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
This medication may cause your urine to turn dark yellow or brown in color. This is usually a harmless, temporary effect and will disappear when the medication is stopped. However, dark brown urine can also be a sign of rare side effects (liver problems or anemia). Therefore, seek immediate medical attention if you notice dark urine along with any of the following symptoms: persistent nausea/vomiting, stomach/abdominal pain, yellowing eyes/skin, tiredness, fast/pounding heartbeat.
Tell your doctor right away if any of these rare but very serious side effects occur: eye pain, vision changes, mental/mood changes, persistent/severe headaches, new signs of infection (e.g., fever, persistent sore throat), easy bruising/bleeding.
Seek immediate medical attention if you develop the following rare but very serious side effects: numbness/tingling of the hands/feet, unusual muscle weakness.
This medication may rarely cause very serious (possibly fatal) lung problems. Lung problems may occur within the first month of treatment or after long-term use of nitrofurantoin (generally for 6 months or longer). Get medical help right away if you develop symptoms of lung problems, including: persistent cough, chest pain, shortness of breath/trouble breathing, joint/muscle pain, bluish/purplish skin.
This medication may rarely cause a severe intestinal condition (Clostridium difficile-associated diarrhea) due to a resistant bacteria. This condition may occur during treatment or even weeks to months after treatment has stopped. Do not use anti-diarrhea or opioid medications if you have the following symptoms because these products may make them worse. Tell your doctor right away if you develop: persistent diarrhea, abdominal or stomach pain/cramping, blood/mucus in your stool.
Use of nitrofurantoin for prolonged or repeated periods may result in oral thrush or a new vaginal yeast infection. Contact your doctor if you notice white patches in your mouth, a change in vaginal discharge, or other new symptoms.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.