“This is the first time we’ve seen a meaningful clinical benefit from an amyloid-targeting therapy,” said Dr. Christopher van Dyck, principal investigator of the lecanemab trial and a researcher at Yale School of Medicine. The drug slowed cognitive decline by 27 percent in people with early Alzheimer’s disease, according to results published in the New England Journal of Medicine.
Eisai and Biogen developed lecanemab. It goes after protofibrils, an intermediate form of amyloid beta that appears to be especially toxic to brain cells. Earlier attempts to clear amyloid plaques had failed.
What the trial found
The Phase 3 trial, called Clarity AD, enrolled 1,795 people with early Alzheimer’s across several countries. Each received lecanemab or a placebo by intravenous infusion every two weeks for 18 months. The main measure was the Clinical Dementia Rating-Sum of Boxes, a combined score of cognitive and everyday function.
People on the drug held on to their abilities for about five months longer than those on placebo. The gains showed up in memory, orientation, language and problem-solving. Brain scans showed amyloid plaques down by as much as 68 percent from baseline.
Van Dyck was frank about the size of the effect. “The 27% reduction in decline may seem modest, but for families dealing with Alzheimer’s, this could mean months of preserved independence and quality time together,” he said. Lecanemab does not cure the disease or undo damage already done.
Side effects
About 21 percent of patients on lecanemab developed brain swelling or bleeding, known as ARIA. Most cases were mild and caused no symptoms. Severe cases needed hospital treatment, and the trial recorded several deaths that may have been linked to these side effects.
Approval and cost
The FDA gave lecanemab accelerated approval in January 2023, based on early data showing plaque reduction. The Clarity AD results support full approval, which would widen insurance coverage. European regulators took a harder line. The European Medicines Agency first declined approval over the balance of risk and benefit, though it has agreed to look again with more safety data and tighter rules on who gets the drug.
Dr. Maria Carrillo, chief science officer at the Alzheimer’s Association, said patients and families “must weigh meaningful but modest benefits against real risks, supported by comprehensive medical oversight.”
The drug costs about $26,500 a year. More than 6 million Americans live with Alzheimer’s, so wide use could cost Medicare billions annually. Treatment also needs clinic administration and MRI monitoring for brain swelling. Medicare currently covers the drug for patients in qualifying clinical studies. Private insurers are drafting policies that typically ask for a specialist evaluation and biomarker confirmation of amyloid.
Researchers are already looking past it. Eli Lilly’s donanemab targets a different form of amyloid, and other teams are testing drugs aimed at tau tangles, neuroinflammation and metabolic dysfunction in brain cells. “Lecanemab likely represents the beginning, not the end, of effective Alzheimer’s treatments,” said Dr. Ronald Petersen, director of the Mayo Clinic Alzheimer’s Disease Research Center. Anyone weighing the drug should talk to their doctor about whether they are in the early stage it was tested in.
