What it is
Abaloparatide is a 34-amino-acid synthetic peptide that builds bone. It is sold as Tymlos, approved in the US on 28 April 2017 for postmenopausal women with osteoporosis at high risk of fracture, and later extended to men with osteoporosis.
Its template is not parathyroid hormone but a close relative: parathyroid hormone-related peptide (PTHrP), a hormone the body uses in growth, lactation and — when tumours overproduce it — in the high calcium of some cancers. The Tymlos label gives the family resemblance in numbers:
| Compared with | Sequence identity |
|---|---|
| PTHrP(1-34) | 76% |
| Parathyroid hormone (1-34) | 41% |
One position is not a natural amino acid at all. Position 29 is Aib — aminoisobutyric acid — a building block the body never puts into proteins, and a common trick for making a peptide hold its shape. The molecule ends in an amide and weighs 3,961 daltons.
How it works
Abaloparatide switches on the PTH1 receptor, the same receptor parathyroid hormone uses. The paradox of this receptor is that a constant signal breaks bone down, while a short daily pulse builds it up. Abaloparatide is built for the pulse: it peaks about half an hour after injection and has a half-life of about 1 hour, with 36% bioavailability under the skin (Tymlos label). The label describes new bone formed on both trabecular (spongy, inner) and cortical (dense, outer) surfaces.
That makes it one of the few anabolic osteoporosis drugs. Most treatments — bisphosphonates such as alendronate, for example — slow the cells that remove bone; they do not add it.
The evidence
The approval rests on one large trial in women and one smaller trial in men, both described on the label.
| Trial | People | Length | Result |
|---|---|---|---|
| Study 003, postmenopausal women | 1,645 | 18 months | New spine fractures 0.6% vs 4.2% with placebo |
| Study 003, non-spine fractures | 1,645 | 19 months | 2.7% vs 4.7%, relative reduction 43%, p = 0.049 |
| Study 019, men | 228 | 12 months | Bone density endpoint; no fracture endpoint |
The spine result is strong: an 86% relative reduction and an absolute one of 3.6 percentage points. The non-spine result only just crossed the line of statistical significance, and the men's approval rests on bone density rather than fractures — both limits the label itself makes visible. After the trial, 1,139 women continued on alendronate for up to 24 more months in an open-label extension (Study 005), which is how the label follows what happens once the course stops.
Doses on the label
Reported as the Tymlos label states it, not as guidance: 80 mcg under the skin of the abdomen once a day, with calcium and vitamin D if the diet falls short. Each pen holds 3.12 mg and is designed to deliver 30 doses of 80 mcg, in 40 microlitres each. Thirty doses come to 2.4 mg, so about 0.72 mg — roughly a quarter of what the cartridge holds — is never delivered; that is the pen's overfill, not a dose.
Safety
The label lists hypersensitivity (including anaphylaxis), osteosarcoma, orthostatic hypotension, hypercalcaemia, and hypercalciuria with kidney stones as warnings. The osteosarcoma warning comes from rat studies of this drug class; the label advises avoiding abaloparatide in people at raised risk of that bone cancer — open growth plates, Paget's disease, bone metastases, prior radiation to the skeleton. The label version dated 11 August 2026 carries no boxed warning. The commonest effects in women were hypercalciuria, dizziness, nausea, headache and palpitations.
Where it stands
FDA application data list one presentation, the 3.12 mg pen, as a current prescription product, with no generic application (2026-09-28). ClinicalTrials.gov holds 25 records with abaloparatide as an intervention. Europe PMC's MEDLINE index holds 367 records naming it in the title or abstract, 31 of them tagged as randomised controlled trials.
Related reading
Abaloparatide's nearest relative in the library is teriparatide, the first 34 amino acids of parathyroid hormone itself and the first anabolic osteoporosis drug; the two act on the same receptor through different templates. For how a chain of amino acids like this one is joined together, see the peptide bond entry.