Calcitonins

Peptide hormones that briefly stop osteoclasts and make the kidney lose calcium. Now used mainly to lower very high calcium quickly.

Updated Nov 1, 2026

What they are

Calcitonin is made by the parafollicular (C) cells of the thyroid. The therapeutic form is synthetic salmon calcitonin, which is more potent and lasts longer in humans than human calcitonin. It is injected for hypercalcaemic emergencies and Paget disease; a nasal spray exists for postmenopausal osteoporosis but is reserved for when other drugs cannot be used, because it has not been shown to reduce fractures and a possible link with cancer was found.

Mechanism of action

Calcitonin binds the calcitonin receptor, a G-protein–coupled receptor on osteoclasts. Osteoclasts shrink and stop resorbing within hours, so calcium and phosphate leave bone more slowly. In the kidney it lowers the tubular reabsorption of calcium, phosphate and sodium. The effect starts quickly but fades with continued use, partly because antibodies can form.

Target: Calcitonin receptor (CALCR), a G-protein–coupled receptor on osteoclasts

Drugs in this class

Calcitonin (salmon)Synthetic salmon calcitonin, injected to lower dangerously high calcium within hours and for Paget disease; a nasal…Calcitonin receptor (CTR), a G-protein–coupled receptor

Test yourself

Think of the answer, then tap the question to see it.

Why is calcitonin useful in a hypercalcaemic emergency?

It lowers serum calcium within hours by stopping osteoclasts and increasing renal calcium loss, while slower drugs such as bisphosphonates start to work.

Why is salmon calcitonin used instead of human calcitonin?

It is more potent and lasts longer in humans than human calcitonin.

Why is calcitonin no longer a preferred drug for osteoporosis?

It has not been shown to reduce fractures, its effect fades, and a meta-analysis suggested a higher rate of malignancy.

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