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Teriparatide (Forteo)
Teriparatide is the drug that proved bone-building — rather than bone-preserving — therapy works in humans: a real PTH(1-34) analog, FDA-approved in 2002 on a large randomized trial showing major fracture reduction. It carried a boxed warning for osteosarcoma from day one, based entirely on a rat carcinogenicity finding, not a human case — and in November 2020, FDA actually removed that warning and the 2-year use limit, after nearly two decades of real-world surveillance found no confirmed human osteosarcoma signal. It's a rare example of a warning genuinely earning its own removal.
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In brief
Should you care? Yes if you've read this site's vosoritide or leuprolide pages — teriparatide is another case of a real, decades-tracked FDA safety signal that moved in a specific, documented direction as more human data came in.The short version
- FDA-approved in 2002 as the first anabolic (bone-forming) osteoporosis drug, versus prior therapies that only slowed bone loss.
- A real 1,637-patient randomized trial (Neer et al., NEJM 2001) backed the approval, cutting new vertebral fractures 65-69% and nonvertebral fractures 53% versus placebo.
- Its boxed warning for osteosarcoma was removed by FDA in November 2020 — based on 18 years of human surveillance data, not a reversal of the original rat finding.
What it is, and its real 2001 trial
Teriparatide is recombinant human parathyroid hormone, amino acids 1-34 — the biologically active fragment of full-length PTH. Unlike bisphosphonates, which slow bone resorption, intermittent PTH(1-34) dosing stimulates new bone formation. The pivotal trial (Neer et al., N Engl J Med 2001;344:1434-1441, PMID 11346808) randomized 1,637 postmenopausal women with a prior vertebral fracture to 20mcg or 40mcg teriparatide or placebo, daily, for a median of 21 months. Both doses cut new vertebral fractures by 65% and 69% respectively versus placebo, and nonvertebral fragility fractures by 53%. FDA approved it (as Forteo, Eli Lilly) in 2002 for osteoporosis in patients at high fracture risk.
Why it carried a boxed warning
Long-term rat carcinogenicity studies conducted during development found an increased incidence of osteosarcoma (a rare, aggressive bone cancer) at rat-relevant lifetime exposures well above human therapeutic dosing. Out of caution, FDA required a boxed warning at approval, plus a 2-year lifetime limit on use — even though no human osteosarcoma case had been linked to the drug in the trial data.
A warning built on rat data, not human cases
The original boxed warning was a precautionary response to an animal carcinogenicity signal, not evidence of harm actually observed in the thousands of patients in teriparatide's human trials.
The 2020 label change
Eli Lilly ran an FDA-required post-marketing surveillance program tracking osteosarcoma incidence in teriparatide-treated patients, including studies linking pharmacy claims data with state cancer registries across large patient cohorts. In November 2020, FDA approved label changes removing both the boxed warning and the 2-year treatment-duration limit, on the basis that 18 years of this surveillance data showed no increased osteosarcoma risk in humans compared with unexposed patients or background population incidence. This is a genuinely rare regulatory sequence — a warning imposed on animal data, tracked for nearly two decades in real patients, and then formally lifted.
What it's used for today
Teriparatide remains indicated for osteoporosis in postmenopausal women and men at high fracture risk, and for glucocorticoid-induced osteoporosis. It's typically prescribed for a defined treatment course (commonly around two years, by convention rather than a hard regulatory limit now) and often followed by an antiresorptive drug to preserve the bone gained. Generic teriparatide is now available alongside the branded product.
References
- Neer RM, Arnaud CD, Zanchetta JR, et al., "Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis," N Engl J Med 2001;344:1434-1441, PMID 11346808.
- FDA approval of Forteo (teriparatide), 2002; original boxed warning for osteosarcoma based on rat carcinogenicity findings.
- FDA label update, November 2020, removing the boxed warning and 2-year treatment limitation, based on ~18 years of post-marketing surveillance (pharmacy-claims/cancer-registry linkage studies) finding no increased human osteosarcoma risk.