Peptide Basics
Calcitonin: The Thyroid’s Calcium-Lowering Peptide, Its Gene Siblings and the Salmon Version Used as Medicine
Calcitonin is a 32-amino-acid peptide hormone made by the C cells of the thyroid gland. It lowers calcium and phosphate in the blood and slows the cells that break down bone. This page sets out what the molecule is, the precursor it shares with procalcitonin and katacalcin, its gene sibling CGRP, how human and salmon calcitonin compare, the receptors it acts on and the calcitonin medicines in FDA’s records. Every figure is taken from UniProt, PubChem, MeSH, MedlinePlus or FDA’s own databases and labels.
What calcitonin is
Calcitonin is one of the peptide hormones. MeSH, the U.S. National Library of Medicine’s subject index, describes it as a peptide hormone that lowers the concentration of calcium in the blood. In humans it is released by thyroid cells and acts to decrease the formation and absorptive activity of osteoclasts, the cells that break down bone. U.S. labels name the cells: the parafollicular cells of the thyroid gland, also called C cells.
UniProt records that calcitonin causes a rapid but short-lived drop in the level of calcium and phosphate in the blood by promoting the incorporation of those ions into bone. MeSH adds that its role in regulating blood calcium is much greater in children and in certain diseases than in normal adults.
The human sequence reads CGNLSTCMLGTYTQDFNKFHTFPQTAIGVGAP, 32 amino acids with an amide on the final proline. Cysteines 1 and 7 are joined by a disulfide bond, which closes the front of the molecule into a ring. PubChem gives it a molecular formula of C151H226N40O45S3 and a molecular weight of 3,417.9 (CID 45055432).
One gene, several peptides: procalcitonin, katacalcin and CGRP
Calcitonin is made from the CALCA gene as part of a precursor of 141 amino acids. UniProt maps it into four pieces:
| Piece | Positions | Amino acids | Note |
|---|---|---|---|
| Signal peptide | 1-25 | 25 | Steers the precursor into the secretory pathway; removed first. |
| N-terminal propeptide | 26-82 | 57 | Cut away during processing; not part of the hormone. |
| Calcitonin | 85-116 | 32 | The hormone. A seven-residue ring at the front, a proline amide at the end. |
| Katacalcin | 121-141 | 21 | A second peptide from the same precursor; UniProt records it as lowering plasma calcium. |
Procalcitonin is the prohormone that calcitonin is cut from. MeSH records that it is normally present in the blood at low levels, but is released into the bloodstream, mainly from neuroendocrine cells in the lungs and intestines, in response to inflammation and bacterial infections, and that it is a diagnostic marker for bacteria in the blood. The first piece is a signal sequence, explained on our signal peptides page.
CGRP, calcitonin gene-related peptide, comes from the same gene by a different route. MeSH describes it as a 37-amino-acid peptide produced by alternative processing of the calcitonin gene’s message, widely distributed in the brain, gut and the nerves around blood vessels, and a potent vasodilator. It is one of the neuropeptides; UniProt records that it widens blood vessels through a receptor built from CALCRL and RAMP1.
Sources: UniProt P01258 and P06881 (CALCA); MeSH D000077740 and D015740. Read 4 November 2026.
Human vs salmon calcitonin
Fish and birds make calcitonin too, in a separate organ, the ultimobranchial gland. Salmon calcitonin is the version most U.S. calcitonin medicines copy. The two molecules share their length, their ring and their proline amide, but half the sequence differs:
| Human calcitonin | Salmon calcitonin | |
|---|---|---|
| Sequence | CGNLSTCMLGTYTQDFNKFHTFPQTAIGVGAP-amide | CSNLSTCVLGKLSQELHKLQTYPRTNTGSGTP-amide |
| Length and shape | 32 amino acids; a ring closed by a disulfide between cysteines 1 and 7 | The same |
| Identical positions | 16 of 32 | 16 of 32 |
| Molecular formula (PubChem) | C151H226N40O45S3 | C145H240N44O48S2 |
| Molecular weight (PubChem) | 3,417.9 | 3,431.9 |
| Where it is made | Parafollicular (C) cells of the thyroid | The ultimobranchial gland, as in other fish and in birds |
| U.S. medicine | Cibacalcin, 1986; discontinued | Calcimar from 1978, Miacalcin and generics; injection still marketed |
Sources: UniProt P01258 and P01263 (calcitonin-1 of the chum salmon, compared position by position); PubChem CID 45055432 and 16220016; current U.S. calcitonin salmon labels (description); Drugs@FDA. Read 4 November 2026.
The calcitonin receptor and its partners
The calcitonin receptor, CALCR, is a G protein-coupled receptor of 474 amino acids that crosses the cell membrane seven times and, UniProt records, activates the cyclic AMP pathway. It does not work alone: three small partner proteins, RAMP1, RAMP2 and RAMP3, pair with it and change which hormones it answers to. The same family of partners turns a related receptor, CALCRL, into the receptor for CGRP:
| Receptor | Activated by | What UniProt records |
|---|---|---|
| Calcitonin receptor (CALCR) alone | Calcitonin, amylin and CGRP | UniProt records that calcitonin acts through CALCR. |
| CALCR + RAMP1 = AMYR1 | Amylin and CGRP | One of the three amylin receptors. |
| CALCR + RAMP2 = AMYR2 | Calcitonin and amylin | UniProt names this complex, with CALCR alone, as calcitonin's receptor. |
| CALCR + RAMP3 = AMYR3 | Amylin | The third amylin receptor. UniProt's CALCR entry adds that all three amylin receptors also respond to calcitonin and CGRP. |
| CALCRL + RAMP1 | CGRP | The CGRP receptor, built on a related receptor, CALCRL. |
This is why calcitonin, amylin and CGRP are studied as one family: they share receptor parts. MeSH notes that calcitonin receptors outside the nervous system carry out calcitonin’s role in calcium balance, while the role of those in the brain is not well understood.
Sources: UniProt P30988 (CALCR), Q16602 (CALCRL), O60894 (RAMP1), O60895 (RAMP2), P01258 and P06881; MeSH D018003. Read 4 November 2026.
Calcitonin as a blood test
Many people meet calcitonin as a lab result rather than a hormone. MedlinePlus, the National Library of Medicine’s health site, says a calcitonin test is most often used to help diagnose C-cell hyperplasia and medullary thyroid cancer in people with symptoms, to find out whether treatment for that cancer is working or whether it has returned, and to screen people with a family history of these conditions or of MEN 2, an inherited disorder caused by changes in the RET gene. Procalcitonin, its precursor, is measured for a different reason, as a marker of bacterial infection.
This page does not give or interpret reference ranges: they differ between laboratories, and a result belongs with the clinician who ordered it.
Sources: MedlinePlus, “Calcitonin test”; MeSH D000077740. Read 4 November 2026.
Calcitonin medicines: what FDA’s records show
Drugs@FDA holds records for calcitonin salmon, made by synthesis and once by recombinant DNA, and for one human-sequence product. The table gives the approval year the database records for each original application and what has happened to it since:
| Medicine | Application | Approved | What the record shows |
|---|---|---|---|
| Calcimar (calcitonin salmon) | NDA 017497 | — | The oldest calcitonin record in Drugs@FDA; the database gives it no approval date. Discontinued. |
| Calcimar (calcitonin salmon) | NDA 017769 | 1978 | The earliest dated approval: an injection. Discontinued. |
| Miacalcin injection (calcitonin salmon) | NDA 017808 | 1986 | Still marketed, with generic injections approved from 2021 to 2026. |
| Cibacalcin (calcitonin human) | NDA 018470 | 1986 | The human sequence as a medicine. Discontinued. |
| Miacalcin nasal spray (calcitonin salmon) | NDA 020313 | 1995 | Discontinued; generic nasal sprays were approved in 2008 and 2009. |
| Fortical (calcitonin salmon, recombinant) | NDA 021406 | 2005 | A nasal spray made by recombinant DNA rather than chemical synthesis. Discontinued. |
The current labels for calcitonin salmon injection name symptomatic Paget’s disease of bone and postmenopausal osteoporosis, both only when other treatments are not suitable, and high blood calcium. The nasal spray labels name postmenopausal osteoporosis in women more than five years past menopause, again when alternatives are not suitable. Both state that a reduction in fractures has not been demonstrated, and both carry the same limitation: because of a possible association between calcitonin salmon and malignancy, the need for continued therapy should be re-evaluated periodically. The injection labels cite a meta-analysis of 21 clinical trials that suggests an increased risk of malignancies overall.
Sources: Drugs@FDA via openFDA (original approval dates and marketing status); current U.S. labels for Miacalcin injection, the calcitonin salmon injection generics and calcitonin salmon nasal spray. Read 4 November 2026. Doses are not reproduced here.
Medibact does not manufacture or sell peptides. We supply USP-grade bacteriostatic water, made in the USA, for research use only, and publish reference material like this page.
Where this sits in the rest of the reference
FAQ
What is calcitonin?
Calcitonin is a peptide hormone of 32 amino acids made by the parafollicular cells, or C cells, of the thyroid gland. MeSH describes it as a hormone that lowers the concentration of calcium in the blood, acting to decrease the formation and activity of osteoclasts, the cells that break down bone. UniProt records that it causes a rapid but short-lived drop in blood calcium and phosphate.
What does calcitonin do in the body?
It lowers calcium and phosphate in the blood by moving those ions into bone, and it slows the osteoclasts that release calcium from bone. MeSH adds an important limit: its role in regulating blood calcium is much greater in children and in certain diseases than in normal adults.
Is calcitonin a peptide or a protein?
A peptide. Human calcitonin is 32 amino acids, CGNLSTCMLGTYTQDFNKFHTFPQTAIGVGAP with an amide at the end, and PubChem gives it a molecular weight of 3,417.9 (CID 45055432). Cysteines 1 and 7 are joined by a disulfide bond, which closes the front of the molecule into a ring. It is cut from a precursor of 141 amino acids.
What is the difference between calcitonin and procalcitonin?
Procalcitonin is the precursor that calcitonin is cut from. MeSH records that it is normally present in the blood at low levels, but is released, mainly from neuroendocrine cells in the lungs and intestines, in response to inflammation and bacterial infections, which is why it is used as a diagnostic marker for bacteria in the blood. Calcitonin itself is the finished hormone of the thyroid's C cells.
How is calcitonin related to CGRP?
Both come from the same gene, CALCA. The gene's message is processed in two ways: one gives the calcitonin precursor, the other gives calcitonin gene-related peptide (CGRP), 37 amino acids. MeSH describes CGRP as a neuropeptide found in the brain, gut and nerves around blood vessels, and a potent vasodilator. UniProt records that CGRP acts mainly through a different receptor, CALCRL with RAMP1.
Why is calcitonin from salmon used as a medicine?
The U.S. medicines are almost all calcitonin salmon: a synthetic polypeptide of 32 amino acids in the same sequence as calcitonin from salmon, as the labels describe it. Salmon and human calcitonin share the same length, ring and proline amide, but are identical at only 16 of 32 positions. A human-sequence product, Cibacalcin, was approved in 1986 and is discontinued.
What is calcitonin used for as a medicine?
Current U.S. labels for calcitonin salmon injection name three uses: symptomatic Paget's disease of bone and postmenopausal osteoporosis, both when other treatments are not suitable, and high blood calcium. The labels state that a reduction in fractures has not been demonstrated, and that because of a possible link between calcitonin salmon and cancer, continued use should be re-evaluated periodically; they cite a meta-analysis of 21 trials.
What is a calcitonin blood test for?
MedlinePlus, the U.S. National Library of Medicine's health site, says a calcitonin test is most often used to help diagnose C-cell hyperplasia and medullary thyroid cancer, to check whether treatment is working or the cancer has returned, and to screen people with a family history of these conditions or of MEN 2. This page does not interpret results; reference ranges vary by laboratory and belong with a clinician.
Is this medical advice?
No. This page explains what calcitonin is, from public scientific and regulatory sources. It gives no dose, schedule, test interpretation or recommendation; anyone treated with these medicines should follow their own clinician and product label. Peptides sold for research are labelled research use only, not for human use. Medibact supplies USP-grade bacteriostatic water, made in the USA, and is not affiliated with any manufacturer of the products named here.
References: UniProt P01258, P06881, P01263, P30988, Q16602, O60894, O60895; MeSH D002116, D000077740, D015740, D018003; PubChem CID 45055432, 16220016; MedlinePlus; Drugs@FDA via openFDA and the current U.S. labels named above. Read 4 November 2026.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.