• Live about 0.3 years longer
• Spend one fewer year in severe dementia
• Gain 0.37 disability-free years
• Spend 0.63 additional years in the community rather than in care

Those gains translated to a lifetime societal value of $104,900 per person. About half came from improved health-related quality of life ($52,300). Reductions in unpaid caregiving added $23,800. Medical cost offsets, mostly captured by Medicaid, contributed $22,200. On an annual basis, Medicaid spending fell by about $1,640, a 13% reduction.

What changes if treatment starts earlier?

Starting donanemab two years sooner, after initial symptoms but before a typical clinical diagnosis, lifted gains across every measure. Lifetime value rose 32%, to $138,300 per person.

The researchers also modeled a more optimistic scenario, reflecting emerging evidence that earlier treatment may slow decline more sharply. In that case, lifetime value reached $179,400, 71% above the clinical-trial group.

Even under conservative assumptions, where donanemab's effect lasts only four years rather than the patient's lifetime, the value roughly halved to $49,100. Earlier treatment still produced 15% more value, or $56,400.

Why earlier matters now

On average, doctors diagnose Alzheimer's about 3.5 years after symptoms first appear. That delay shrinks the window in which treatment can do the most.

"New therapies and diagnostic tools are making it possible to alter the course of Alzheimer's disease, but they come with considerable costs," Chapel said. "Our research suggests that investments in early detection could help ensure that patients start treatments when they're more likely to provide the greatest benefit to patients and society."

Chapel is a USC Schaeffer scholar and assistant research professor at the USC Price School of Public Policy.

Several FDA-approved blood-based biomarker tests, released in the past year, plus digital cognitive tools, could make earlier detection more practical. Coverage rules, drug costs, and the difficulty of identifying eligible patients have so far limited uptake.

What could future treatments achieve?

The model also tested hypothetical drugs. A therapy that slows decline by 50% would generate $208,700 to $276,700 in lifetime societal value, depending on timing. A drug that halts progression altogether would produce $530,000 to $648,300. More than 150 Alzheimer's drugs are currently in clinical testing.

"As therapies and diagnostic tools continue to improve, the case for finding and treating people sooner only gets stronger," Chapel said. "Every year between the first symptoms and a diagnosis is value lost for patients, their families and the public programs that ultimately pay for dementia care."

What are the caveats?

The projections rely on assumptions about how trial results extend across a full lifetime. Donanemab is new, so how long its benefits persist remains uncertain. The model omits drug costs and screening expenses, which would shrink the net financial value. Researchers describe the work as a tool for policy planning rather than a prediction for any individual patient.

Alzheimer's and related dementias will cost the United States an estimated $818 billion in 2026. As the population ages, that burden is expected to grow, sharpening the case for earlier intervention.