What it is
Calcitonin is a 32-amino-acid hormone made by the thyroid gland. It comes from the thyroid's parafollicular cells, often called C cells, which sit between the follicles that make thyroid hormone. UniProt's record for human calcitonin (P01258) places it at residues 85–116 of a 141-residue precursor:
- sequence CGNLSTCMLGTYTQDFNKFHTFPQTAIGVGAP;
- a ring closed by a disulfide bond between the cysteines at positions 1 and 7;
- an amidated proline at the end.
The same precursor yields a second peptide, katacalcin (21 amino acids), which UniProt also annotates as lowering plasma calcium.
What it does
UniProt's function annotation: calcitonin causes a rapid but short-lived drop in blood calcium and phosphate by promoting their incorporation into bone. It acts through the calcitonin receptor (CALCR) and through a receptor complex of CALCR with the accessory protein RAMP2 — one of the receptors amylin also uses. Calcium is otherwise managed mainly by parathyroid hormone, whose drug fragments are recorded in teriparatide and abaloparatide.
Why the medicine is salmon's
The medicine is calcitonin salmon, a synthetic copy of the hormone fish make in their ultimobranchial gland (Miacalcin label). Set side by side, the two are the same length with the same ring, but differ at 16 of 32 positions:
| Sequence (1–32) | |
|---|---|
| Human (UniProt P01258) | CGNLSTCMLGTYTQDFNKFHTFPQTAIGVGAP |
| Salmon (UniProt P01263) | CSNLSTCVLGKLSQELHKLQTYPRTNTGSGTP |
Because it is a foreign sequence, the label warns that circulating antibodies to calcitonin salmon may develop and may cause loss of response.
What the label says
Miacalcin injection (NDA 017808; label effective 2024-09-15) contains 200 USP units per mL for injection under the skin or into muscle. Its label lists:
| Indication | Stated limit |
|---|---|
| Symptomatic Paget's disease of bone | Moderate to severe disease; when alternatives are not suitable |
| Hypercalcaemia | — |
| Postmenopausal osteoporosis | When alternatives are not suitable; fracture reduction not demonstrated |
The label's doses are 100 USP units daily for Paget's disease and osteoporosis, and a weight-based schedule starting at 4 USP units/kg every 12 hours for hypercalcaemia.
Two warnings stand out. Malignancy: in a meta-analysis of 21 randomised controlled trials of calcitonin salmon (nasal spray or investigational oral forms), malignancies were reported in 4.1% of treated patients against 2.9% on placebo, and the label asks for periodic re-evaluation of continued therapy. Hypersensitivity: serious reactions, including deaths from anaphylaxis, have been reported.
Where it stands
Calcitonin salmon remains FDA-listed as Miacalcin injection and as generic injections and nasal sprays (openFDA, 2026-10-04). PubMed returns 41,327 records for calcitonin, 1,031 tagged as randomised controlled trials. The human hormone itself is not sold as a medicine.
Related reading
Calcitonin's closest relative is amylin, whose altered copy pramlintide is an approved drug. For the other side of calcium control, see the parathyroid-hormone fragment teriparatide.