Romosozumab (Evenity)

Romosozumab is a genuinely different kind of bone drug from anything else in this site's osteoporosis cluster — a monoclonal antibody against sclerostin that builds new bone and slows its breakdown at the same time, rather than doing only one or the other the way teriparatide, abaloparatide, calcitonin and denosumab each do. It reached the market first in Japan in January 2019, but its US approval was delayed by more than a year after the FDA required a second, dedicated cardiovascular-safety trial — real, adjudicated evidence of a heart attack and stroke signal that shaped the drug's final US label from day one.

A dual-acting mechanism, not another antiresorptive

Every other drug in this site's osteoporosis cluster does one job: calcitonin and denosumab slow bone breakdown, while teriparatide and abaloparatide stimulate new bone formation. Romosozumab, developed by Amgen and UCB, does both from a single mechanism: it's a humanized monoclonal antibody against sclerostin, a protein secreted by bone cells that normally restrains osteoblast (bone-building) activity. Blocking sclerostin releases that brake, increasing bone formation, while simultaneously reducing bone resorption — a real, dual pharmacological action distinct from every other drug on this site's bone-density pages.

The FRAME trial

Romosozumab's core efficacy evidence comes from FRAME (Cosman F, Crittenden DB, Adachi JD, et al., "Romosozumab Treatment in Postmenopausal Women with Osteoporosis," N Engl J Med 2016;375(16):1532-1543, PMID 27641143, DOI: 10.1056/NEJMoa1607948), a randomized, double-blind, placebo-controlled trial of 7,180 postmenopausal women with a T-score of -2.5 to -3.5, given monthly 210mg subcutaneous romosozumab or placebo for 12 months, after which both groups switched to denosumab for a further 12 months. At 12 months, romosozumab reduced new vertebral fractures by 73% versus placebo (a real, large, statistically significant effect), and the fracture-risk reduction was largely preserved through the second year once both groups moved onto denosumab — the same drug covered on this site's own denosumab page.

The ARCH trial, and the signal that delayed US approval

A second Phase 3 trial, ARCH (Saag KG, Petersen J, Brandi ML, et al., "Romosozumab or Alendronate for Fracture Prevention in Women with Osteoporosis," N Engl J Med 2017;377(15):1417-1427, PMID 28892457, DOI: 10.1056/NEJMoa1708322), randomized 4,093 postmenopausal women with a prior fragility fracture to monthly romosozumab or weekly oral alendronate for 12 months, both followed by open-label alendronate. Romosozumab reduced fractures more than alendronate did — but during the first 12 months, adjudicated major adverse cardiovascular events (heart attack, stroke, cardiovascular death) occurred in 2.5% of the romosozumab group versus 1.9% of the alendronate group, an imbalance that hadn't appeared in the earlier, placebo-controlled FRAME trial. In July 2017, the FDA issued Amgen a Complete Response Letter declining to approve romosozumab as submitted, and required the ARCH cardiovascular data to be incorporated into a resubmitted application before it would reconsider — a real, substantive delay driven by a specific safety finding, not a routine administrative holdup.

Japan first, the US three months later — with a boxed warning

Romosozumab reached its first market anywhere in Japan, where the Ministry of Health, Labour and Welfare approved it (as Evenity, via the Amgen Astellas BioPharma joint venture) on 8 January 2019. The FDA followed three months later, approving Evenity (romosozumab-aqqg) on 9 April 2019 for postmenopausal women with osteoporosis at high risk of fracture — but only with a boxed warning stating that romosozumab may increase the risk of heart attack, stroke and cardiovascular death, and a contraindication against starting it in anyone who has had either event within the preceding year. An FDA advisory committee had voted 18-1 in January 2019 in favor of approval, but specifically recommended the boxed warning as a condition of that vote — a case where the drug's efficacy case was strong enough to clear an advisory panel even after a real cardiovascular signal, provided the label disclosed it plainly.

Current status

Evenity remains FDA-approved and actively co-marketed by Amgen and UCB, and is typically prescribed for a defined 12-month course — often followed by an antiresorptive drug such as denosumab or a bisphosphonate to preserve the bone gained, the same sequencing FRAME's own extension phase tested. Later pharmacovigilance analyses of real-world adverse-event reporting have produced mixed reassurance about the magnitude of the original ARCH cardiovascular signal, but the boxed warning and 12-month prior-cardiovascular-event contraindication remain on the current US label as of this review — worth checking directly if a current label change matters to you. As a specialty osteoporosis biologic administered by injection under medical supervision, romosozumab has no wellness, bodybuilding or grey-market presence of any kind.