New long-term data suggests anti-amyloid monoclonal antibody (mAb) drugs — including lecanemab (Leqembi) and donanemab (Kisunla) — may help slow cognitive decline in people with early Alzheimer’s disease for several years. Cognitive decline involves the gradual loss of thinking skills like memory, reasoning, attention, and language.

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After three to four years of treatment, people taking these drugs continued to decline more slowly — and in some cases showed slight improvements — compared to those not treated.

What Are Anti-Amyloid Monoclonal Antibodies?

Anti-amyloid monoclonal antibodies are a type of disease-modifying therapy designed to target one of Alzheimer’s hallmark features: the buildup of amyloid beta plaques in the brain.

These laboratory-made antibodies attach to amyloid proteins and help the body clear them away. Over time, reducing these plaques may help protect brain cells and slow the progression of Alzheimer’s symptoms.

Lecanemab and donanemab are the first of these medications to gain full approval from the U.S. Food and Drug Administration (FDA) for treating early Alzheimer’s disease. Both require confirming amyloid buildup before starting treatment, typically through a PET scan or spinal fluid test. People taking these drugs require ongoing brain monitoring to check for side effects.

How the Research Was Done — and What It Found

The new findings come from long-term extension studies that followed people who had completed earlier clinical trials of Leqembi and Kisunla.

In the four-year study extension, people treated continuously with lecanemab showed a 1.75-point slower decline on a common Alzheimer’s measure called the Clinical Dementia Rating — Sum of Boxes (CDR-SB), compared to the expected decline in untreated individuals. Among people with low tau levels (a marker of early disease), 56 percent improved or stayed stable in memory and daily functioning after four years.

In a separate three-year follow-up study of donanemab, people treated with the drug had a 1.2-point slower decline in CDR-SB scores compared with expected outcomes. Those who began treatment early had a 27 percent lower risk of progressing to the next stage of Alzheimer’s.

Together, these findings indicate that the benefits of treatment with anti-amyloid antibodies appear to grow over time.

Side Effects and Safety

The main safety concern with both lecanemab and donanemab remains amyloid-related imaging abnormalities (ARIA) — brain swelling or small bleeds seen on MRI scans. Researchers have found that 20 percent of people taking lecanemab may develop brain swelling or bleeding. The figure is 35 percent for those taking donanemab, though the risk is lower for those on a modified dosing schedule.

In a long-term study of lecanemab, ARIA rates decreased after the first year and remained consistent through four years of treatment. Donanemab’s updated dosing schedule may also help lower ARIA risk by as much as 41 percent.

Still, people taking these drugs require regular monitoring for ARIA and other changes.

Why It Matters

For decades, Alzheimer’s treatments mainly managed symptoms without affecting the underlying disease. The new data suggests anti-amyloid therapies like lecanemab and donanemab may help slow cognitive decline, especially when started early and continued over time.

However, doctors caution that these treatments are not a cure, and they come with logistical challenges such as IV infusions, testing requirements, and high costs.

Even so, the possibility of slowing cognitive decline over several years marks a meaningful advance in Alzheimer’s care and offers renewed hope for people living with the disease and their loved ones.

If you or someone you care for is exploring Alzheimer’s treatment options, it’s important to talk with a healthcare provider about what’s available, how these therapies work, and whether they are right for your situation.

Learn more about treatment options available for Alzheimer’s.

Join the Conversation

On myALZteam, people share their experiences with Alzheimer’s, get advice, and find support from others who understand.

Have you or your loved one considered anti-amyloid treatments like lecanemab or donanemab? Let others know in the comments below.