Constipation may occur. This could lead to other problems such as hemorrhoids and bowel obstruction. If constipation persists or worsens, contact your doctor or pharmacist promptly.If your doctor has directed you to use this medication, remember that 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.To minimize constipation, drink plenty of fluids and exercise. Using an antacid that contains magnesium along with this product can help prevent constipation. Stool softeners may also be helpful. Ask your doctor or pharmacist about other antacids, stool softeners and laxatives.Aluminum-containing antacids bind to phosphate, an important body chemical, in the gut. This can cause low phosphate levels if your kidneys are normal, especially if you use large doses for a long time. Tell your doctor immediately if you have any of the following symptoms of low phosphate: loss of appetite, unusual tiredness, muscle weakness.Seek immediate medical attention if any of these rare but very serious side effects or symptoms of a serious medical problem occur: black/tarry stools, mental/mood changes (e.g., confusion, deep sleep), pain with urination, stomach/abdominal pain, vomit that looks like coffee grounds.A very serious allergic reaction to this drug is rare. However, seek immediate medical attention 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.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.