Calcitonin is a peptide that is produced and secreted by the chief cells of the thyroid gland. This peptide has a direct effect on osteoclasts by decreasing their size and inhibiting their ability to resorb bone.

Calcitonin is directly regulated by serum calcium level. When serum calcium levels are high, the chief cells respond by producing and secreting more calcitonin in order to decrease bone breakdown and thereby decrease the mobilization of calcium. Calcitonin has been used to treat several diseases in which osteoclast resorption of bone is uncontrolled. It also may have a role in decreasing the longterm effects of osteoporosis.