To judge a new Alzheimer's drug, look past the headline percentage and weigh four things: the absolute size of the benefit, how long it was measured, the safety risks, and whether you or your family member even qualify. A "35% slowing of decline" can mean a fraction of a point on a clinical scale over 18 months—real, but modest. This page explains how to read those claims using the two approved anti-amyloid drugs, Leqembi and Kisunla, as working examples. These are IV antibodies that clear beta-amyloid, a protein plaque linked to Alzheimer's, and they are meant only for early-stage disease.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- Start with absolute effect, not the percentage
- Who actually qualifies?
- Weigh the safety risk honestly
- Count the real-world cost and burden
- A quick checklist for any new Alzheimer's drug
- Frequently Asked Questions
Start with absolute effect, not the percentage
Drug makers lead with relative numbers because they sound large. Lecanemab (brand name Leqembi) slowed decline by 27% versus placebo in its Phase 3 CLARITY-AD trial, according to the study published in the New England Journal of Medicine. Donanemab (Kisunla) showed 35% slowing in its trial. The percentage is only half the story. that 27% for lecanemab equals an absolute difference of 0.45 points on the CDR-SB, a scale that runs 0 to 18.
Ask what the raw point difference is, and whether a clinician or family would actually notice it in daily life. Also pin down the time frame. Both results were measured at roughly 18 months. "Slowing" means the disease still progressed in treated patients—just somewhat slower. These drugs do not stop or reverse Alzheimer's.
Who actually qualifies?
A drug's value is zero if the person can't take it. Both approved antibodies are limited to early Alzheimer's—mild cognitive impairment or mild dementia—not moderate or severe stages, per Medicare's coverage page.
Eligibility also requires proof of amyloid in the brain, confirmed by a PET scan or spinal fluid (CSF) test. A memory complaint or a general Alzheimer's diagnosis is not enough. before assuming a new drug applies, check these basics:.
- Is the disease still in the early, mild stage?
- Has amyloid been confirmed by PET or CSF testing?
- Is there a provider nearby who administers IV infusions and does the required monitoring?
Weigh the safety risk honestly
Both drugs carry a boxed warning—the FDA's strongest—for ARIA, or amyloid-related imaging abnormalities. ARIA means brain swelling or small bleeds, often silent but sometimes serious. In the lecanemab trial, ARIA-E (swelling) occurred in 12.6% of patients and ARIA-H (bleeding) in 17.3%. Genetics change this math sharply.
People who carry two copies of the APOE4 gene face far higher risk: symptomatic ARIA-E ran about 9.2% in these carriers versus 1.4% in non-carriers, according to an FDA-referenced NCBI review. The FDA recommends APOE genotype testing before starting treatment. A fair value judgment sets the modest benefit against this risk. For a two-copy APOE4 carrier, the risk-benefit balance looks very different than for a non-carrier.
Count the real-world cost and burden
Approval does not mean easy access. Medicare covers both drugs only for their FDA-approved use, and it requires the treating clinician to enter each patient's data into a nationwide CMS registry, as described on Medicare's coverage page.
The practical burden adds up: regular IV infusions, repeat MRI scans to watch for ARIA, amyloid confirmation testing, and a participating provider. For rural families, travel alone can be a deciding factor. Factor these in before calling a drug "worth it." A treatment with a small measurable benefit may still be reasonable for one family and not for another, depending on stage, genetics, distance, and tolerance for risk.
A quick checklist for any new Alzheimer's drug
When the next drug is announced, run it through the same filter rather than the press release: If a claim can't survive these five questions, the headline number alone tells you little.
- What is the absolute effect size, and over how many months?
- Does "slowing" mean the disease still progressed?
- What stage and test results are required to qualify?
- What are the serious risks, and do genetics raise them?
- What does treatment demand—infusions, scans, registry, travel?
Frequently Asked Questions
Does full FDA approval mean a drug is proven to work well?
It means the FDA judged benefits to outweigh risks for a specific group. Lecanemab won traditional approval in July 2023 and donanemab in July 2024, but both offer modest, not curative, benefits.
Can these drugs help someone with moderate or advanced Alzheimer's?
No. Both are approved only for early symptomatic disease with confirmed amyloid, not moderate or severe dementia.
