Calcitonin is a 32-amino-acid peptide hormone. In humans it is made by the parafollicular cells (also called C cells) of the thyroid gland, and it gets released when blood calcium runs high. Its job is to push calcium back down. It does that mainly by shutting down the cells that dissolve bone.
That single action is the whole story of the drug. The cell it targets is the osteoclast, the bone-resorbing cell. When calcitonin binds its receptor on an osteoclast, the cell pulls in its ruffled border, retracts, and stops chewing on bone within minutes. The effect runs through a Gs-coupled, cyclic-AMP pathway. Calcitonin also nudges the kidney to excrete more calcium in urine. Both effects lower serum calcium (StatPearls, NCBI Bookshelf; Physiological Reviews, 2018).
Why salmon, not human
Most calcitonin given as a drug is salmon calcitonin (also written salcatonin). Salmon calcitonin differs from the human version across roughly amino acids 10 to 27, and that difference makes it bind the human receptor more tightly and last longer in the body. So it is more potent as a medicine than human calcitonin, which is the practical reason the salmon form took over (StatPearls).
One quirk: the effect fades. Within a few days of dosing, osteoclasts downregulate their calcitonin receptors, so the calcium-lowering punch weakens. Clinicians call this tachyphylaxis, and it limits how useful calcitonin is for anything long-term.
What it was used for
Salmon calcitonin reached the market as an injection and later as a nasal spray, sold under names like Miacalcin (Novartis) and the recombinant Fortical. Approved uses have included:
- Paget's disease of bone, where bone turnover is abnormally fast
- Hypercalcemia, including the high calcium seen in some cancers
- Postmenopausal osteoporosis, historically its biggest market
For osteoporosis, the evidence was always thin. Trials suggested salmon calcitonin could cut the rate of new spine fractures in postmenopausal women, but it never showed a benefit for hip or other non-spine fractures, which are the fractures that matter most (Bone Health & Osteoporosis Foundation).
The cancer signal and the regulatory turn
The osteoporosis story ended badly. In 2012 the European Medicines Agency reviewed pooled trial data and found that patients on calcitonin for long stretches developed cancer more often than those on placebo. The excess ran from about 0.7% with oral formulations to 2.4% with the nasal spray. The EMA concluded calcitonin should not be used for osteoporosis at all, and that any calcitonin use should be short-term, for indications like Paget's disease, immobilization-related bone loss, and cancer-related high calcium (EMA review, 2012).
The US followed. In 2013 a joint FDA advisory committee voted 12 to 9 against continued marketing of calcitonin-salmon nasal spray for osteoporosis, citing weak benefit and the cancer concern. A supporting meta-analysis put the relative risk of any malignancy at roughly 1.5 times that of controls (Medscape, 2013). The mechanism behind the association was never pinned down, and researchers have described the link as weak rather than proven. But the risk-benefit math no longer worked for a non-life-threatening condition with better alternatives.
Buyer and quality notes
Proper calcitonin-salmon products are prescription drugs made by pharmaceutical manufacturers, not research-grade powders. Peptide labeled "calcitonin" sold outside that channel as a research chemical is not approved for human consumption, and there is no reliable way to confirm its identity or purity without a certificate of analysis (COA) from third-party testing of that specific lot. Identity and purity matter especially for a 32-residue peptide, where folding and the internal disulfide bridge affect whether the molecule is even active.
Nothing here is medical or dosing advice. Calcitonin's own regulatory history is a reminder that "natural hormone" does not mean "safe to take indefinitely."