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Evidence · for healthcare professionals

How osteoporosis drugs work: bone builders and bone savers

Dr Aditya Aggarwal, MS (Ortho), PMC 45581, Aggarwal Clinic, Patiala
Last reviewed · next review 18 October 2027

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On this page 5 sections
  1. Two kinds of bone drug
  2. Bone builders
  3. Bone savers
  4. What changes management
  5. Related evidence pages

Evidence summary for clinicians. For discussion, not a prescription. Grades are a GRADE-style reading of the cited sources unless a guideline grade is quoted.

Two kinds of bone drug

Bone is renewed all the time. Osteoclasts remove old bone and osteoblasts lay down new bone. Bone-building (anabolic) drugs push formation ahead of removal for a limited time. Bone-saving (antiresorptive) drugs slow removal. This difference explains the order of treatment covered in sequential and combination therapy.

Bone builders

Teriparatide: PTH(1-34), daily injection

A daily pulse of parathyroid hormone switches on osteoblasts, so bone formation runs ahead of resorption. In postmenopausal women with vertebral fractures, 20 µg daily cut new vertebral fractures from 14% to 5% (RR 0.35)1. The effect fades after 12 to 18 months, and the new bone is lost unless an antiresorptive follows2.

Abaloparatide: PTHrP(1-34) analogue

It binds the same PTH1 receptor in a conformation that gives a shorter signal3. Formation rises with less resorption and less high calcium (3.4% vs 6.4% with teriparatide), and it cut vertebral and non-vertebral fractures against placebo over 18 months4.

Romosozumab: anti-sclerostin antibody, monthly for 12 months only

Sclerostin from osteocytes brakes bone formation. Blocking it raises formation and lowers resorption at the same time, so BMD rises fast (spine +11.3% at 12 months)5. The building effect wanes sooner than with PTH drugs. Serious heart and stroke events were 2.5% vs 1.9% against alendronate in year 16, so this risk should be checked first7.

Evidence grade: High for fracture reduction with all three builders (RCTs).

Bone savers

Bisphosphonates: alendronate, zoledronate

They stick to bone mineral, are taken up by osteoclasts and block the enzyme FPPS, which osteoclasts need to work8. They stay in bone for years, so the effect fades slowly after stopping9. Zoledronate 5 mg yearly cut vertebral fractures by 70% over 3 years10.

Denosumab: anti-RANKL antibody, every 6 months

It blocks RANKL, the signal that makes and drives osteoclasts11. The effect is fully reversible. If a dose is missed, turnover rises above baseline by 6 months and BMD is back to baseline by 12 months. Vertebral fractures then rise to untreated rates, often several at once12.

Raloxifene: a SERM

It acts like oestrogen on bone and raises BMD, without stimulating the endometrium13. It lowers radiographic vertebral fractures but not clinical fractures14.

Evidence grade: High for bisphosphonates and denosumab; moderate for raloxifene (vertebral benefit only).

What changes management

  • Builder first in very high risk. Builders need active remodelling surfaces, and a potent saver given first blunts them. Hip BMD falls for up to 24 months when teriparatide follows denosumab15, 16.
  • Never stop denosumab abruptly. Give zoledronate 6 months after the last dose17.
  • Always follow a builder with a saver, planned at the start18.
DrugClassTargetOffset after stopping
TeriparatideBuilderPTH1 receptorNew bone lost unless a saver follows2
AbaloparatideBuilderPTH1 receptor (shorter signal)As teriparatide2
RomosozumabBuilder and saverSclerostinBuilding effect wanes sooner than with PTH drugs2
Alendronate, zoledronateSaverFPPS in osteoclastsSlow; drug stays in bone for years8
DenosumabSaverRANKLFast; turnover rebounds within 6 months12
RaloxifeneSaver (mild)Oestrogen receptorNot covered in the cited sources

Where the evidence is weak

  • Much of the data on the order of drugs is BMD, not fractures16, 15.
  • The abaloparatide mechanism comes from a laboratory study3.

Questions

Common questions

What is the difference between anabolic and antiresorptive drugs?
Anabolic drugs (teriparatide, abaloparatide, romosozumab) raise bone formation for a limited time. Antiresorptives (bisphosphonates, denosumab, raloxifene) slow the removal of bone by osteoclasts.
Why does the effect of denosumab end quickly?
Denosumab blocks RANKL and is fully reversible. If a dose is missed, bone turnover rises above baseline by 6 months and BMD returns to baseline by 12 months.
Why do bisphosphonates keep working after stopping?
They bind bone mineral and stay in bone for years, so their effect fades slowly after stopping.
What is the main safety check before romosozumab?
Heart and stroke risk. In ARCH, serious heart and stroke events in year 1 were 2.5% with romosozumab against 1.9% with alendronate.

For patients

Plain-language guides

References18 sources, linked to PubMed or DOI

Verified by PMID and DOI. Vancouver style.

  1. 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. PubMed 11346808 · doi:10.1056/NEJM200105103441904
  2. Ferrari S, Thouverey C, Gerbaix M. Mechanisms underlying the waning of osteoanabolic therapy effects in osteoporosis. J Bone Miner Res. 2026. PubMed 41841800 · doi:10.1093/jbmr/zjag053
  3. Hattersley G, Dean T, Corbin BA, et al. Binding Selectivity of Abaloparatide for PTH-Type-1-Receptor Conformations and Effects on Downstream Signaling. Endocrinology. 2016. PubMed 26562265 · doi:10.1210/en.2015-1726
  4. Miller PD, Hattersley G, Riis BJ, et al. Effect of Abaloparatide vs Placebo on New Vertebral Fractures in Postmenopausal Women With Osteoporosis: A Randomized Clinical Trial. JAMA. 2016. PubMed 27533157 · doi:10.1001/jama.2016.11136
  5. McClung MR, Grauer A, Boonen S, et al. Romosozumab in postmenopausal women with low bone mineral density. N Engl J Med. 2014. PubMed 24382002 · doi:10.1056/NEJMoa1305224
  6. Saag KG, Petersen J, Brandi ML, et al. Romosozumab or Alendronate for Fracture Prevention in Women with Osteoporosis. N Engl J Med. 2017. PubMed 28892457 · doi:10.1056/NEJMoa1708322
  7. Shoback D, Rosen CJ, Black DM, et al. Pharmacological Management of Osteoporosis in Postmenopausal Women: An Endocrine Society Guideline Update. J Clin Endocrinol Metab. 2020. PubMed 32068863 · doi:10.1210/clinem/dgaa048
  8. Russell RG, Watts NB, Ebetino FH, et al. Mechanisms of action of bisphosphonates: similarities and differences and their potential influence on clinical efficacy. Osteoporos Int. 2008. PubMed 18214569 · doi:10.1007/s00198-007-0540-8
  9. LeBoff MS, Greenspan SL, Insogna KL, et al. The clinician's guide to prevention and treatment of osteoporosis. Osteoporos Int. 2022. PubMed 35478046 · doi:10.1007/s00198-021-05900-y
  10. Black DM, Delmas PD, Eastell R, et al. Once-yearly zoledronic acid for treatment of postmenopausal osteoporosis. N Engl J Med. 2007. PubMed 17476007 · doi:10.1056/NEJMoa067312
  11. Cummings SR, San Martin J, McClung MR, et al. Denosumab for prevention of fractures in postmenopausal women with osteoporosis. N Engl J Med. 2009. PubMed 19671655 · doi:10.1056/NEJMoa0809493
  12. Cummings SR, Ferrari S, Eastell R, et al. Vertebral Fractures After Discontinuation of Denosumab: A Post Hoc Analysis of the Randomized Placebo-Controlled FREEDOM Trial and Its Extension. J Bone Miner Res. 2018. PubMed 29105841 · doi:10.1002/jbmr.3337
  13. Delmas PD, Bjarnason NH, Mitlak BH, et al. Effects of raloxifene on bone mineral density, serum cholesterol concentrations, and uterine endometrium in postmenopausal women. N Engl J Med. 1997. PubMed 9385122 · doi:10.1056/NEJM199712043372301
  14. Ayers C, Kansagara D, Lazur B, et al. Effectiveness and Safety of Treatments to Prevent Fractures in People With Low Bone Mass or Primary Osteoporosis: A Living Systematic Review and Network Meta-analysis for the American College of Physicians. Ann Intern Med. 2023. PubMed 36592455 · doi:10.7326/M22-0684
  15. Cosman F, Nieves JW, Dempster DW. Treatment Sequence Matters: Anabolic and Antiresorptive Therapy for Osteoporosis. J Bone Miner Res. 2017. PubMed 27925287 · doi:10.1002/jbmr.3051
  16. Cosman F, Kendler DL, Langdahl BL, et al. Romosozumab and antiresorptive treatment: the importance of treatment sequence. Osteoporos Int. 2022. PubMed 35165774 · doi:10.1007/s00198-021-06174-0
  17. Tsourdi E, Zillikens MC, Meier C, et al. Fracture risk and management of discontinuation of denosumab therapy: a systematic review and position statement by ECTS. J Clin Endocrinol Metab. 2020. PubMed 33103722 · doi:10.1210/clinem/dgaa756
  18. Gregson CL, Armstrong DJ, Avgerinou C, et al. The 2024 UK clinical guideline for the prevention and treatment of osteoporosis. Arch Osteoporos. 2025. PubMed 40921943 · doi:10.1007/s11657-025-01588-3

This article is for healthcare professionals. It is not medical advice for individual patients and doesn’t replace clinical judgement or a consultation.

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