Leqembi vs. Kisunla: How the Two Alzheimer’s Antibody Drugs Compare

Leqembi (lecanemab, from Eisai and Biogen) and Kisunla (donanemab, from Eli Lilly) are the two antibody drugs approved in the US to treat early Alzheimer’s disease. Both clear amyloid, the protein that forms plaques in the Alzheimer’s brain, and both modestly slow decline. For patients and families, the practical differences between them — dosing, duration, side effects and cost — often shape the choice. Here is how they compare.

Who can take them

Both are for people with early symptomatic Alzheimer’s: mild cognitive impairment or mild dementia due to Alzheimer’s. Before starting, patients need confirmation of amyloid, by PET scan, spinal fluid test, or increasingly an FDA-cleared blood test, and a baseline MRI. Neither drug is meant for moderate or advanced dementia, and neither reverses memory loss.

How well they work

In its pivotal trial, Leqembi slowed decline on a standard clinical scale by about 27% over 18 months compared with placebo. Kisunla slowed decline by up to about 35% on a combined measure over 18 months in people with lower levels of tau, another Alzheimer’s protein. The trials used different scales and populations, so the numbers can’t be compared directly. In practical terms, both drugs give people a few extra months at a milder stage, on average; many families find that meaningful, while critics say the effect is small for the risks and burden involved.

How they are given

Leqembi starts as an intravenous infusion every two weeks, with the dose based on body weight. After 18 months, patients can switch to an infusion every four weeks, or to Leqembi Iqlik, a once-weekly injection under the skin using an autoinjector pen that can be given at home, approved in August 2025.

Kisunla is a fixed-dose infusion of about 30 minutes every four weeks. Since July 2025, its label uses a gentler start, stepping the dose up over the first three infusions (350 mg, 700 mg, 1,050 mg, then 1,400 mg), which lowered the risk of brain swelling without reducing amyloid clearance.

How long treatment lasts

This is one of the biggest differences. Kisunla is designed to be stopped once amyloid is cleared on a PET scan, which in trials happened for many patients within 6 to 12 months. Leqembi is intended as ongoing treatment, on the view that continued dosing keeps amyloid and related proteins suppressed. A time-limited course means fewer infusions and potentially lower total cost; continuous treatment offers ongoing suppression but a longer commitment.

The main risk: ARIA

Both drugs can cause amyloid-related imaging abnormalities (ARIA): brain swelling (ARIA-E) and small bleeds (ARIA-H). Most cases cause no symptoms and are found on scheduled MRIs, but some cause headache, confusion, dizziness or vision changes, and rare cases have been serious or fatal. In Leqembi’s trial, ARIA-E occurred in about 13% of patients (symptomatic in about 3%). Kisunla’s original dosing produced ARIA-E in about 24%; the newer, gradual schedule reduced that to roughly 14% in the first six months. Patients on either drug need regular MRI monitoring, especially early in treatment.

Risk is highest in people who carry two copies of the APOE4 gene, so genetic testing is recommended before starting, and people taking blood thinners need particular caution. For more on APOE4 and the brain’s blood vessels, see our coverage of recent research.

What treatment involves day to day

Beyond the drug itself, treatment is a logistical commitment. Patients usually need a care partner to help with appointments, regular trips to an infusion center (every two or four weeks), and several MRI scans in the first months to check for ARIA, with more if symptoms appear. New headaches, confusion, dizziness or vision problems should be reported promptly. For many families, the distance to an infusion center and the availability of specialist appointments shape the decision as much as the drug data do.

What they cost

Leqembi lists at roughly $26,500 a year for the IV form. Kisunla’s total cost depends on how long someone stays on it: estimates range from about $12,500 for six months to nearly $49,000 for 18 months. Those figures exclude the substantial costs of infusions, MRI scans, PET scans and specialist visits. Medicare covers both drugs for eligible patients, with clinicians required to take part in a registry, and the usual Part B coinsurance applies, so out-of-pocket costs depend heavily on supplemental coverage. The home-injected Iqlik falls under Part D, where 2026 out-of-pocket costs are capped at $2,100 a year.

How to think about the choice

There is no head-to-head trial, and many specialists see the two as broadly similar in benefit. Practical factors often decide: whether a finite course or ongoing treatment appeals, how easy it is to travel for infusions (and whether home injections are possible later), a person’s APOE4 status and other bleeding risks, insurance, and what the local memory clinic offers. Both require a commitment to scans and monitoring. The decision is best made with a neurologist or memory specialist who can weigh individual risks. This explainer is general information, not medical advice.