Teriparatide vs Abaloparatide: How Bone Building Peptides Work and What the Fracture Trials Found

Teriparatide (Forteo) and abaloparatide (Tymlos) are the two FDA approved peptides that build new bone. Both are daily injections that activate the parathyroid hormone type 1 receptor, and both cut new vertebral fractures sharply in randomized trials of women with postmenopausal osteoporosis.

Most osteoporosis drugs you have probably heard of, such as alendronate, risedronate and denosumab, are antiresorptive, which means they slow the cells that break bone down. Teriparatide and abaloparatide are anabolic, meaning they switch on the cells that lay new bone down, and that difference is why endocrinologists often reach for them when someone has already fractured or has very low bone density. This article walks you through how the two peptides work, what each major trial measured, how they compare on side effects and dosing, and why the drug that follows them matters almost as much as the peptide itself. It is educational content about published research and is not medical advice.

Bone building peptides work by stimulating osteoblasts, the cells that form new bone, while most other osteoporosis drugs work by restraining osteoclasts, the cells that resorb it. Your skeleton is remodeled constantly, with osteoclasts digging small cavities and osteoblasts refilling them, and in osteoporosis the digging outpaces the refilling until bone becomes thinner and more porous.

Antiresorptive drugs work by slowing the digging, which preserves what is there and lets bone density creep up a little, but they do not rebuild much of the architecture that has already been lost. Teriparatide and abaloparatide add new bone tissue on top of existing surfaces, which is why bone mineral density at the spine rises faster on these peptides than on most antiresorptive drugs.

The bone building effect depends on timing, because parathyroid hormone that stays high all day, as it does in the disease primary hyperparathyroidism, drains calcium from the skeleton, whereas a short daily pulse of the same signal does the opposite and favors bone formation. A once daily injection of teriparatide or abaloparatide produces that brief pulse and then clears from your body.

Teriparatide is a recombinant copy of the active end of human parathyroid hormone, known as PTH(1-34). According to the current FDA label, Forteo is approved for postmenopausal women with osteoporosis at high risk for fracture, for men with primary or hypogonadal osteoporosis at high risk for fracture, and for men and women with osteoporosis linked to long term glucocorticoid (steroid) therapy.

The labeled dose of teriparatide is 20 mcg injected under the skin of the thigh or abdomen once a day, and each Forteo pen delivers 28 daily doses.

The Neer trial, published in the New England Journal of Medicine in 2001, established that teriparatide prevents fractures. Neer and colleagues randomized 1637 postmenopausal women who already had vertebral fractures to teriparatide 20 or 40 mcg daily or placebo, with a median observation period of 21 months.

New vertebral fractures occurred in 14% of women on placebo, 5% on the 20 mcg dose and 4% on the 40 mcg dose. The relative risks were 0.35 and 0.31, which works out to roughly a two thirds reduction in new spine fractures. New nonvertebral fragility fractures (wrist, hip, rib and similar breaks from minor falls) fell from 6% on placebo to 3% in each teriparatide group.

Bone density moved in the same direction as the fracture results. Compared with placebo, teriparatide 20 mcg and 40 mcg raised lumbar spine bone mineral density by 9 and 13 more percentage points and femoral neck density by 3 and 6 more points. The 40 mcg dose built more bone but did not prevent more fractures and caused more side effects, which is why 20 mcg became the approved dose.

Abaloparatide is a synthetic peptide modeled on parathyroid hormone related protein (PTHrP), a close cousin of parathyroid hormone that acts on the same receptor. The FDA label describes Tymlos as a PTHrP analog and lists an initial US approval in 2017.

Tymlos is approved for postmenopausal women with osteoporosis at high risk for fracture and, since a later label expansion, to increase bone density in men with osteoporosis at high risk for fracture. The labeled dose is 80 mcg injected under the skin of the abdomen around the navel once daily, and each pen delivers 30 doses.

Abaloparatide was designed to favor the bone building side of PTH receptor signaling while producing a smaller rise in blood calcium, and the ACTIVE trial supports the calcium part of that design goal.

The ACTIVE trial, published in JAMA in 2016, compared abaloparatide with placebo and included an open label teriparatide arm. ACTIVE enrolled 2463 postmenopausal women with a mean age of 69 at 28 sites in 10 countries, and participants received placebo (n=821), abaloparatide 80 mcg (n=824) or teriparatide 20 mcg (n=818) daily for 18 months.

According to the Tymlos prescribing information, new vertebral fractures at 18 months occurred in 0.6% of women on abaloparatide and 4.2% on placebo. That is an absolute risk reduction of 3.6% and a relative risk reduction of 86%, and the JAMA paper also reports that the Kaplan Meier rate of nonvertebral fractures was lower with abaloparatide than with placebo.

The safety comparison with teriparatide is the most useful head to head signal ACTIVE offers. Hypercalcemia (high blood calcium) occurred in 3.4% of women on abaloparatide and 6.4% on teriparatide. Because the teriparatide arm was open label and the trial was not designed to compare fracture rates between the two peptides, ACTIVE does not show that one peptide prevents more fractures than the other.

In women with severe osteoporosis, the VERO trial showed that teriparatide prevented more fractures than risedronate. VERO, published in The Lancet in 2018, was the first osteoporosis trial to compare two drugs using new fractures as the primary outcome. It randomized 680 women to each arm, giving either teriparatide 20 mcg daily plus a weekly placebo pill or risedronate 35 mg weekly plus daily placebo injections for 24 months, and every participant had at least two moderate or one severe vertebral fracture at entry.

At 24 months, new vertebral fractures occurred in 28 women (5.4%) on teriparatide and 64 women (12.0%) on risedronate, a risk ratio of 0.44. Clinical fractures, meaning fractures that caused symptoms, occurred in 4.8% versus 9.8% (hazard ratio 0.48). Nonvertebral fragility fractures were 4.0% versus 6.1%, but that difference (hazard ratio 0.66, p=0.10) was not statistically significant.

VERO was funded by Lilly, which makes Forteo. It remains the strongest direct evidence that an anabolic peptide outperforms a standard first line pill in people at very high fracture risk.

Both peptides are approved for men, although the male evidence is based on bone density rather than fracture counts. The ATOM trial, published in the Journal of Bone and Mineral Research in 2022, randomized 228 men aged 40 to 85 with osteoporosis 2:1 to abaloparatide 80 mcg (n=149) or placebo (n=79) for 12 months, and the men had a mean age of 68.3.

At 12 months, lumbar spine bone mineral density rose 8.48% on abaloparatide versus 1.17% on placebo. Total hip density rose 2.14% versus 0.01%, and femoral neck density rose 2.98% versus 0.15%. The trial was too small and too short to measure fracture reduction, which is why the Tymlos label for men says "to increase bone density" rather than promising fewer fractures.

The bone you gain on teriparatide or abaloparatide is not locked in when the injections stop, so an antiresorptive drug is usually needed afterward to hold and extend the gains. Both labels also limit how long these peptides are typically used: the Tymlos label says use for more than 2 years during a lifetime is not recommended, and the Forteo label says use beyond 2 years should only be considered if fracture risk remains high.

The ACTIVExtend study tested that handoff directly. Women who finished ACTIVE on abaloparatide (558 women) or placebo (581 women) were switched to alendronate for up to 24 months. Over the full 43 months, 0.9% of the abaloparatide then alendronate group had a new vertebral fracture versus 5.6% of the placebo then alendronate group, an 84% relative risk reduction, and a supplemental analysis found no hip fractures in the abaloparatide then alendronate group versus five in the placebo then alendronate group.

The order of the drugs also appears to matter. The DATA-Switch study, published in The Lancet in 2015, followed women who switched between teriparatide and denosumab. Over 48 months, total hip bone mineral density rose 6.6% when teriparatide came first and denosumab followed, but only 2.8% when denosumab came first and teriparatide followed. Spine density rose 18.3% versus 14.0%, a difference that was not statistically significant. Because DATA-Switch was small (it grew out of a 94 woman trial), it measured bone density rather than fractures.

The most common side effects of both peptides are dizziness, nausea, headache, palpitations and injection site reactions, and both can cause a temporary drop in blood pressure when you stand up. The Tymlos label says this orthostatic hypotension typically appears within 4 hours of an injection, which is why both labels advise taking the first doses somewhere you can sit or lie down.

In the abaloparatide trial in women, dizziness was reported by 10% of participants on Tymlos versus 6% on placebo, and adverse reactions of orthostatic hypotension by 1% versus 0.5%. Calcium related effects are the other main category, since both peptides can raise blood and urine calcium. Both labels advise avoiding use in people with an underlying hypercalcemic disorder such as primary hyperparathyroidism, and the Forteo label advises weighing the risk in people with active or recent kidney stones.

The osteosarcoma boxed warning on teriparatide was removed in 2020. Forteo was originally approved with a boxed warning about osteosarcoma, a rare bone cancer, and a 2 year lifetime limit on use, because rats given high doses for most of their lives developed the tumor.

Human data did not bear the concern out. A 15 year US postmarketing surveillance study (Gilsenan and colleagues, Journal of Bone and Mineral Research, 2021) tracked osteosarcoma cases diagnosed from 2003 to 2016. With a background rate of about 2.5 cases per million adults aged 40 or older each year, the study expected 4.17 cases among people previously treated with teriparatide and found 3, a standardized incidence ratio of 0.72. A Lilly authored review (Krege and colleagues, JBMR Plus, 2022) describes how this and other real world data led to the 2020 label update, which removed the boxed warning and revised the 2 year limit.

Both current labels still advise avoiding these peptides in people with a raised baseline risk of osteosarcoma, including children and young adults with open growth plates, people with Paget's disease of bone, bone metastases or prior skeletal cancer, people who have had radiation therapy involving the skeleton, and people with hereditary conditions that predispose to osteosarcoma.

The table below puts the labeled details and the main trial results for the two peptides next to each other so you can see where they differ.

No trial was designed to compare fracture prevention between teriparatide and abaloparatide, so the choice between them usually comes down to calcium tolerance, label indication, insurance coverage and which drug will follow.

Teriparatide and abaloparatide are not research peptides; they are FDA approved prescription drugs with labeled doses, manufacturing standards and decades of trial data behind them. They are prescribed after a bone density scan and a fracture risk assessment, and they come with lab monitoring for calcium. The fracture results above apply to those approved products used in the populations studied, mostly postmenopausal women with established osteoporosis, and they do not carry over to unregulated peptides sold online, to people with normal bone density, or to uses such as injury recovery.

If you or someone you love has osteoporosis with a prior fracture or very low bone density, teriparatide and abaloparatide are the peptides with the strongest fracture evidence in this whole field. Both cut new spine fractures sharply in randomized trials, teriparatide beat a standard bisphosphonate head to head in VERO, and abaloparatide caused less hypercalcemia in ACTIVE. The part that is easy to overlook is what comes next, because the gains need an antiresorptive drug afterward to last, so a good plan with your doctor covers the full sequence rather than the injections alone.

Neer RM and colleagues, Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis, New England Journal of Medicine, 2001, doi.org/10.1056/NEJM200105103441904. Miller PD and colleagues, Effect of Abaloparatide vs Placebo on New Vertebral Fractures in Postmenopausal Women With Osteoporosis (ACTIVE), JAMA, 2016, doi.org/10.1001/jama.2016.11136. Kendler DL and colleagues, Effects of teriparatide and risedronate on new fractures in post menopausal women with severe osteoporosis (VERO), The Lancet, 2018, doi.org/10.1016/S0140-6736(17)32137-2. Bone HG and colleagues, ACTIVExtend, Journal of Clinical Endocrinology and Metabolism, 2018, doi.org/10.1210/jc.2018-00163. Czerwinski E and colleagues, The Efficacy and Safety of Abaloparatide in Men With Osteoporosis (ATOM), Journal of Bone and Mineral Research, 2022, pubmed.ncbi.nlm.nih.gov/36190391. Leder BZ and colleagues, Denosumab and teriparatide transitions in postmenopausal osteoporosis (DATA-Switch), The Lancet, 2015, doi.org/10.1016/S0140-6736(15)61120-5. Gilsenan A and colleagues, Teriparatide Did Not Increase Adult Osteosarcoma Incidence in a 15 Year US Postmarketing Surveillance Study, Journal of Bone and Mineral Research, 2021, doi.org/10.1002/jbmr.4188. Krege JH and colleagues, Teriparatide and Osteosarcoma Risk, JBMR Plus, 2022, doi.org/10.1002/jbm4.10665. TYMLOS (abaloparatide) and FORTEO (teriparatide) US prescribing information, FDA, accessed October 2026. This article is educational and is not medical advice.