What it is
Parathyroid hormone is an 84-amino-acid hormone made by four pea-sized glands in the neck. Its sequence begins SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF… and runs to 84 residues (full sequence in the strip above). It is cut from a 115-residue precursor: a 25-residue signal peptide and a 6-residue propeptide are removed first (UniProt P01270). The drug labels agree on which part does the work — the Yorvipath label calls the first 34 amino acids "the biologically active region."
At 84 residues PTH is more than twice the 40-amino-acid line in 21 CFR 600.3, so US regulation counts it as a protein. That is visible in how its drugs were filed: full-length PTH (Natpara) as a biologic licence, BLA 125511; the 34-residue teriparatide as a drug application. See peptide vs protein.
How it works
PTH has one job: keep calcium in the blood within a narrow range. MedlinePlus describes the loop plainly — when blood calcium is too low, the parathyroid glands release PTH, which tells bone to release calcium, helps the intestine absorb it and acts on the kidneys. UniProt's summary adds the machinery:
| Target | What PTH does |
|---|---|
| Receptor | Binds PTH1R, activating cAMP/PKA and PLC/PKC signalling |
| Bone | Acts on osteoblast-lineage cells, raising RANKL and lowering OPG, which drives osteoclasts to resorb bone and free calcium |
| Kidney | Keeps calcium in the blood (MedlinePlus); removes the phosphate transporter from kidney cells, so more phosphate is excreted (UniProt, inferred from animal data) |
| Vitamin D | Switches on the kidney enzyme CYP27B1, raising active vitamin D (1,25-dihydroxyvitamin D3), which increases calcium absorption from food (UniProt, inferred from animal data) |
The body's partner hormone pulling the other way is calcitonin, from the thyroid. A second, related peptide, PTHrP, shares PTH1R; its drug copy is abaloparatide, 41% identical to PTH(1-34) (Tymlos label).
The paradox the drugs exploit
Continuously high PTH, as in an overactive gland, removes bone to supply calcium. A brief daily pulse of the 34-residue front end does the reverse on balance: teriparatide cut new spine fractures from 14.3% to 5.0% in its main trial and is gone from the blood within about three hours (Forteo label, covered in that entry). The timing of exposure, not a different molecule, separates the two effects.
Drugs made from PTH
| Drug | What it is | Use | First US approval |
|---|---|---|---|
| Natpara | Recombinant full-length PTH (84 residues) | Hypoparathyroidism | 2015-01-23 (BLA 125511) |
| Teriparatide (Forteo and others) | PTH(1-34) | Osteoporosis at high fracture risk | see the teriparatide entry |
| Yorvipath (palopegteriparatide) | PTH(1-34) on a 40 kDa PEG carrier, released slowly | Hypoparathyroidism in adults | 2024-08-09 (NDA 216490) |
Two status notes, both as read: Drugs@FDA still lists Natpara as Prescription (data 2026-10-16), yet DailyMed returns no current label for it (search 2026-10-17); the library records both and makes no inference about supply. In Yorvipath's 26-week phase 3 trial (NCT04701203), 42 of 61 adults (68.9%) met a composite endpoint — calcium in the normal range with no active vitamin D and no more than 600 mg/day of calcium — vs 1 of 21 on placebo (4.8%) (label). Its label warns of hypersensitivity reactions and of serious high and low calcium, and limits use to one injection a day. Dosing in every case is titrated by the treating endocrinologist against calcium results.
The PTH blood test
PTH is also one of the commonest peptide lab tests. MedlinePlus describes the PTH test as measuring "the level of parathyroid hormone (PTH)" in blood, read together with calcium to work out whether the glands are over- or under-active or responding to something else. The interpretation of any single result belongs to the clinician who ordered it; the library's other lab-test peptides are BNP and NT-proBNP and procalcitonin.
Where it stands
- Approved forms: full-length PTH as Natpara (2015); PTH(1-34) as teriparatide and, PEG-linked, as Yorvipath (2024).
- Research record: PubMed indexes 50,522 records for "parathyroid hormone", 1,892 tagged as randomised controlled trials; ClinicalTrials.gov lists 625 studies naming it as an intervention (2026-10-17).
Related reading
The 34-residue drug cut from PTH is teriparatide; the PTHrP-based alternative is abaloparatide; PTH's opposite number in calcium control is calcitonin.