Key takeaways
- Leqembi (lecanemab) and Kisunla (donanemab) are anti-amyloid antibodies, drugs that clear amyloid plaque from the brain, approved by the FDA for early Alzheimer’s disease.
- In 18-month trials, Leqembi slowed decline by 27% on the CDR-SB scale, and Kisunla slowed decline by 35% on its main scale compared with placebo.
- Neither drug stops or reverses Alzheimer’s; people on treatment still declined, only more slowly.
- Both carry a boxed warning for ARIA, brain swelling or small bleeds seen on MRI; about 21% of Leqembi patients and about 37% of Kisunla patients had ARIA in trials, and most cases caused no symptoms.
- Only people with mild cognitive impairment or mild dementia and confirmed amyloid qualify, which is why an earlier diagnosis now changes the options.
Leqembi and Kisunla are the first Alzheimer’s drugs shown to slow the disease itself; older drugs only ease symptoms for a while. That is real progress after decades of failed trials. They are also not cures, and they are not for everyone with memory loss.
So the question for families is personal: would slowing progression, without stopping it, be meaningful to you?
What are Leqembi and Kisunla?
Leqembi (lecanemab, from Eisai and Biogen) and Kisunla (donanemab, from Eli Lilly) are monoclonal antibodies that bind to beta-amyloid and help the immune system clear it from the brain. Amyloid plaques are one of the two hallmark changes of Alzheimer’s disease.
The FDA gave Leqembi traditional approval in July 2023 and approved Kisunla in July 2024. Both started as IV infusions given at an infusion center. Leqembi is given every two weeks at first; Kisunla is given every four weeks and can be stopped once scans show the amyloid has cleared.
These drugs are different from older Alzheimer’s medicines such as donepezil (Aricept), which help with symptoms for a time but do not change the course of the disease.
How much do Leqembi and Kisunla slow Alzheimer’s?
Leqembi and Kisunla slow Alzheimer’s modestly. Here is what the main trials found over 18 months, compared with placebo:
| Drug | Trial | Slowing of decline | ARIA in trial |
|---|---|---|---|
| Leqembi (lecanemab) | CLARITY AD | 27% on CDR-SB | 21.3% of patients |
| Kisunla (donanemab) | TRAILBLAZER-ALZ 2 | 35% on iADRS; 36% on CDR-SB | About 37% of patients |
What do those percentages mean in daily life? On the CDR-SB scale, people on Leqembi declined by 1.21 points over 18 months and people on placebo declined by 1.66 points. The difference is 0.45 points on an 18-point scale. Researchers still argue about whether a person or family would notice that.
There are other ways to look at it. In the Kisunla trial, 47% of patients showed no decline on the CDR-SB at one year, compared with 29% on placebo, and patients had a 39% lower risk of moving to the next stage of the disease. Some families describe the benefit as more months of driving, cooking or managing their own medications.
Longer follow-up suggests the gap may grow. Eisai reported that after four years, Leqembi patients had declined less than expected for similar untreated patients, though that comparison was not against a placebo group.
What can’t Leqembi and Kisunla do?
Leqembi and Kisunla cannot stop Alzheimer’s, restore lost memory or help people in the moderate or severe stages. People taking them in trials still got worse; they got worse more slowly.
They also do nothing for other causes of dementia, such as vascular dementia, Lewy body dementia or frontotemporal dementia. And most clinical trial participants were white, so how well the results apply to Black, Hispanic and Asian American patients is less certain.
What is ARIA, and how risky are these drugs?
ARIA, short for amyloid-related imaging abnormalities, is swelling (ARIA-E) or small bleeds (ARIA-H) in the brain that show up on MRI. It is the main safety risk of these drugs, and both carry an FDA boxed warning for it.
Most ARIA causes no symptoms and is found on the scheduled MRIs that patients get during treatment. A review in The Lancet in 2025 put symptomatic ARIA at about 3% to 6% of patients. Serious cases are rare, but deaths have been reported in trials.
Risk depends heavily on the APOE4 gene. In the Leqembi trial, people with two copies of APOE4 had a 32.6% rate of ARIA-E, compared with 5.4% for people with no copies. That is why doctors usually recommend APOE genetic testing before treatment, and why people taking blood thinners need extra caution.
Who qualifies for Leqembi or Kisunla?
The people who qualify for Leqembi or Kisunla have mild cognitive impairment or mild dementia due to Alzheimer’s, plus confirmed amyloid on a PET scan, spinal fluid test or, increasingly, a blood test. They also need to be able to get regular MRIs and, for IV treatment, get to infusion appointments.
People are often ruled out if they have had several small brain bleeds, a recent stroke or take certain blood thinners. Medicare covers both drugs for eligible patients when the prescribing doctor takes part in a registry.
This is the main reason early diagnosis gets so much attention now. By the time many families seek help, the person has moved past the mild stage.
What questions should you ask about anti-amyloid treatment?
Ask your neurologist:
- Does the person meet the criteria, and how do we confirm amyloid?
- What is their APOE4 status, and how does it change the risk?
- How often are infusions and MRIs, and how far is the nearest center?
- What will we pay after Medicare or insurance?
- What signs of ARIA should we watch for between scans? (Headache, confusion, vision changes and dizziness are the common ones.)
- If we decide against treatment, what else can help?
Saying no is a legitimate choice. Some people decide the travel, scans and risk are not worth a modest slowing. Others decide every extra month at their current level is worth it. Both are informed decisions when made with the facts.
Dementia Capable CARES discusses treatment questions in its Brain Health 2026 series. Learn more at dementiacapablecares.org.
This article is educational and is not medical advice.
Sources
- Leqembi reduced biomarkers of Alzheimer’s, slowed cognitive decline at 18 months, Healio, May 2023
- Lilly’s Alzheimer’s data set a new high score in slowing cognitive decline, Fierce Biotech
- Review shows lecanemab and donanemab slow decline and explains who should get them, News-Medical, September 2025
- New Alzheimer’s drugs showing success slowing disease progression, Norton Healthcare
- Leqembi vs. Kisunla: An Alzheimer’s Drug Point-by-Point Comparison, Being Patient
