What it is
Teriparatide is a 34-amino-acid peptide drug: the first 34 amino acids of parathyroid hormone (PTH), which in full is 84 amino acids long. The Forteo label calls this front section the hormone's "biologically active region," and states that teriparatide binds the same receptors with the same affinity as the corresponding part of natural PTH.
Its sequence is identical to human PTH(1-34):
SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF
It is made by E. coli bacteria modified with recombinant DNA and weighs 4,117.8 daltons. Cutting the hormone to 34 amino acids also moves it across a regulatory line: at 84 amino acids PTH is a protein; at 34, teriparatide is a peptide.
How it works — the pulse is the point
Natural PTH is, in the label's words, the primary regulator of calcium and phosphate metabolism in bone and kidney: it regulates bone turnover, how much calcium and phosphate the kidney keeps, and calcium absorption from the gut.
What teriparatide does to bone depends on how it is given. The label states that its skeletal effects "depend upon the pattern of systemic exposure": a once-daily injection stimulates new bone formation, preferentially switching on osteoblasts (the cells that build bone) over osteoclasts (the cells that remove it). The pharmacokinetics make the pulse visible — after a 20 mcg injection, levels peak at about 30 minutes and fall below measurable levels within 3 hours, with a half-life of about an hour.
That is why teriparatide is described as anabolic: most osteoporosis drugs slow the removal of bone, while this one stimulates new bone to be laid down.
What it is approved for
| Who | Approved use (Forteo label) |
|---|---|
| Postmenopausal women | Osteoporosis at high risk for fracture, or after other treatments failed or were not tolerated; reduces vertebral and non-vertebral fractures |
| Men | Increasing bone mass in primary or hypogonadal osteoporosis at high fracture risk |
| Men and women on long-term steroids | Osteoporosis linked to daily prednisone 5 mg or more (or equivalent) at high fracture risk |
The trial record
The label's main study randomised 1,637 postmenopausal women with osteoporosis — 90% of whom already had at least one spine fracture — to daily teriparatide or placebo, with calcium and vitamin D for everyone. Median treatment was 19 months.
| Outcome | Placebo | Teriparatide 20 mcg |
|---|---|---|
| New vertebral fractures | 14.3% | 5.0% |
That is roughly nine fewer spine fractures per 100 women over the trial — counted on X-rays, so not all of them would have been felt as symptoms, as the label points out.
The osteosarcoma question
Rats given teriparatide developed osteosarcoma, a bone cancer, more often. The current Forteo label (Lilly, August 2026) handles it as a warning and precaution, not a boxed warning:
- osteosarcoma has been reported in patients after marketing;
- observational studies in humans have not found an increased risk;
- data on risk beyond 2 years of use are limited;
- it should be avoided in people at higher baseline risk — open growth plates (children and young adults), Paget's disease and other metabolic bone diseases, bone metastases or skeletal cancers, and prior radiation to the skeleton.
On duration, the label says use for more than 2 years in a lifetime should be considered only if the patient remains at, or has returned to, high fracture risk.
Where it stands
FDA application data list 4 teriparatide applications on 2026-09-24: Forteo (2002), Bonsity (2019) and two generics, the first approved in November 2023. PubMed indexes 4,012 records, 286 tagged as randomised controlled trials.
Related reading
Osteoporosis after menopause is one of the approved uses covered in peptides for menopause. For contrast with the many bone and tissue claims made for unapproved compounds, see peptides for joints and tendons. The 40-amino-acid line that makes teriparatide a peptide and PTH a protein is explained in the peptide-or-protein entry.