Constipation or stomach upset may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. If your doctor has directed you to use this medication, remember that 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. Tell your doctor right away if you have any serious side effects, including: nausea/vomiting, loss of appetite, unusual weight loss, mental/mood changes, signs of kidney problems (such as change in the amount of urine), bone/muscle pain, headache, increased thirst, increased urination, weakness, tiredness, 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: 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.

Some products that may interact with this drug include: digoxin, phosphate binders. Calcium can decrease the absorption of other drugs such as tetracycline antibiotics (for example, doxycycline, minocycline), bisphosphonates (such as alendronate), estramustine, levothyroxine, and quinolone antibiotics (such as ciprofloxacin, levofloxacin). Also, certain medications can decrease the absorption of vitamin D (bile acid sequestrants such as cholestyramine/colestipol, mineral oil, orlistat). Separate your doses of these medications as far as possible from your doses of calcium/vitamin D. Ask your doctor or pharmacist about how long you should wait between doses and for help finding a dosing schedule that will work with all your medications. Check the labels on all your prescription and nonprescription/herbal products (such as antacids, laxatives, vitamins) because they may contain calcium, phosphate, or vitamin D. Ask your pharmacist about using those products safely. Vitamin D is very similar to calcitriol. Do not use medications containing calcitriol while using vitamin D. This product may interfere with certain lab tests (such as cholesterol tests), possibly causing false test results. Make sure lab personnel and all your doctors know you use this product.