Calcium carbonate-containing products reduce acidity in the stomach. The reduction of acid decreases the absorption of iron from the intestine. Therefore, doses of calcium and iron should be separated by a several hours.
Calcium products also bind to sodium polystyrene sulfonate (Kayexalate, a drug used to treat high levels of potassium) in the intestine and, therefore, may interfere with the action of Kayexalate. Doses of Kayexalate and calcium products should be separated by several hours.
NURSING MOTHERS: Calcium products appear in breast milk but are considered safe during breastfeeding.
SIDE EFFECTS: Calcium products rarely cause an upset stomach. However, excessive intake or absorption of calcium may lead to increased levels of calcium in the blood (hypercalcemia) which may cause nausea, vomiting, decreased appetite, abdominal pain, dry mouth and thirst. Severe hypercalcemia may cause confusion, delirium, stupor, and coma. Calcium supplements cause rebound stomach acidity.
Reference: FDA Prescribing Information
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