Calcitonin is a 32 amino acid single chain polypeptide hormone produced by the thyroid gland which interacts with parathyroid hormone in the regulation of bone turnover and hence in the maintenance of calcium balance. Calcitonin acts to lower the serum levels of calcium and phosphate.

Secretion of calcitonin is stimulated by hypercalcaemia. However, high levels of calcitonin are not associated with hypocalcaemia.

There are two forms of calcitonin commercially available, salmon and porcine. The former is more suitable for long-term drug treatment because antibodies form more readily to the porcine form of the preparation.