Phytates in bran and whole grains can reduce absorption. Anticonvulsants may reduce serum calcium levels. Use of cardiac glycosides with parenteral calcium preparations may increase the risk of cardiac arrythmias. Prolonged use of laxatives can reduce calcium absorption. Loop diuretics increase calcium excretion.
Tamoxifen use with calcium supplements can result in hypercalcemia.
Thiazide diuretics may reduce calcium excretion. Fluoride may reduce the absorption of calcium and vice-versa, should be given 2 hours apart. Calcium carbonate or calcium phosphate may reduce the absorption of iron, should be given 2 hours apart. Calcium may reduce the absorption of zinc. Anorexia, arrhythmia, arthralgia, bradycardia, confusion, constipation, depression, drowsiness, dry mouth, headache, hypertension, increased thirst, metallic taste, mild flatulence, myalgia, nausea, polyuria, skin rash, vomiting, weakness.