Headache, nausea, vomiting, joint pain, diarrhea, abdominal pain, fever, sore throat, trouble sleeping, or loss of appetite may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.Remember that this medication has been prescribed because your doctor 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.Rarely, balsalazide can worsen ulcerative colitis. Tell your doctor right away if your symptoms worsen after starting this medication (for example, if you have increased abdominal pain, rectal bleeding).Tell your doctor right away if you have any serious side effects, including: nausea/vomiting that doesn't stop, signs of kidney problems (such as change in the amount of urine), yellowing eyes/skin, dark urine, unusual/extreme tiredness, severe stomach/abdominal pain, burning/painful urination, fast/pounding heartbeat.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: fever, swollen lymph nodes, 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.