No, neither Leqembi nor Kisunla can restore memory already lost to Alzheimer’s disease. Both medications are designed to slow cognitive decline in early-stage disease, not to reverse damage that has already occurred. If someone has forgotten their grandchildren’s names or lost the ability to recognize familiar faces, these drugs cannot bring those memories back.
What they can do—and this matters significantly—is help preserve remaining cognitive function and potentially prevent some of that future memory loss from happening in the first place. Leqembi (lecanemab), approved by the FDA in its full traditional form in July 2023, and Kisunla (donanemab), approved in July 2024, represent a new class of Alzheimer’s treatments called anti-amyloid monoclonal antibodies. Both target the sticky protein plaques that accumulate in the brains of people with Alzheimer’s, but neither acts as a memory restoration therapy. Understanding this distinction—between slowing decline and reversing it—is critical for anyone considering these treatments or supporting someone who might benefit from them.
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
- What Do These Medications Actually Do?
- How Much Decline Do These Drugs Actually Slow?
- Why Haven’t These Drugs Restored Memory in Anyone?
- How Do Leqembi and Kisunla Differ From Each Other?
- What About Side Effects and Amyloid-Related Imaging Abnormalities?
- Real-World Uptake and Patient Persistence
- What This Means for Someone With Early Alzheimer’s
- Frequently Asked Questions
What Do These Medications Actually Do?
Both leqembi and Kisunla work through the same fundamental mechanism: they are monoclonal antibodies that target and help clear beta-amyloid plaques from the brain. Leqembi binds to amyloid-beta protein and removes it; Kisunla specifically targets N-truncated pyroglutamate amyloid-beta, a form considered particularly toxic. In clinical terms, this plaque clearing is real and measurable—brain imaging shows reduced amyloid burden in patients taking these drugs. However, the removal of amyloid plaques does not translate into restored memory. The plaques may have contributed to the death of brain cells, and dead cells do not regenerate.
What reducing amyloid does accomplish is slower future decline. Think of it this way: if Alzheimer’s disease is a wall crumbling brick by brick, these medications do not put bricks back in place or repair existing damage. Instead, they slow the rate at which new bricks fall. A person on Leqembi or Kisunla is not regaining lost cognitive function; they are experiencing a slower rate of loss compared to what would happen without treatment. This is still clinically meaningful, but it is not memory restoration.
How Much Decline Do These Drugs Actually Slow?
The clinical trial data provides specific numbers about what “slowing decline” means in practice. In the CLARITY AD trial for Leqembi, patients showed a mean difference of −0.45 points on the CDR-SB (Clinical Dementia Rating-Sum of Boxes) scale over 18 months compared to placebo. This was statistically significant, but it represented a slowing of decline, not improvement. Over three years of continuous treatment, patients on Leqembi showed cognitive decline of −0.95 on the CDR-SB versus the expected untreated decline, and more than 50% of patients showed stability rather than progression in cognitive function.
Kisunla showed similar results in its TRAILBLAZER-ALZ 2 trial, slowing cognitive decline by 35% compared to placebo. At one year, 47% of Kisunla patients showed no cognitive decline at all, compared to 29% of those receiving placebo. Over three years, Kisunla patients showed a CDR-SB decline of −0.6 at 18 months and −1.2 at 36 months, with benefits that actually increased over time. Across both drugs, research shows that anti-amyloid monoclonal antibodies slow cognitive and functional decline by approximately 30% in early-stage Alzheimer’s disease. These numbers matter to families, but they should be understood for what they are: slowed decline, measured in fractions of a cognitive scale, not restored memories or reversed disease.
Why Haven’t These Drugs Restored Memory in Anyone?
The reason these drugs cannot restore memory comes down to basic neurobiology. Amyloid plaques and tau tangles are thought to trigger a process of neurodegeneration—the death and shrinkage of nerve cells—but removing the plaques does not bring dead neurons back to life. If amyloid-related damage has already killed brain cells in the regions responsible for storing or retrieving memories, clearing amyloid does not reverse that cell death. The drugs work by preventing further amyloid accumulation and possibly slowing further neuronal damage, but they operate after significant damage has already been done.
This is why both medications are approved only for mild cognitive impairment or mild dementia—the earliest symptomatic stages of Alzheimer’s disease. The FDA eligibility requirements specify this explicitly: these drugs are not approved for moderate or advanced dementia. At those later stages, amyloid plaques may no longer be the primary driver of cognitive symptoms, and the neuronal damage is too extensive for amyloid clearance alone to make a difference. By the time someone has moderate dementia, expecting either drug to restore lost memories would be unrealistic given current neuroscience.
How Do Leqembi and Kisunla Differ From Each Other?
While both medications slow cognitive decline through amyloid removal, they differ in administration and, importantly, in one unique capability of Kisunla. Leqembi is given as an intravenous infusion every two weeks for a lead-in phase and then every four weeks for maintenance. In July 2026, the FDA approved Leqembi IQLIK, a subcutaneous formulation that can be injected under the skin, offering patients an alternative to regular IV visits. Kisunla is also given as an IV infusion every four weeks after a titration phase.
The most significant difference is that Kisunla is currently the only anti-amyloid monoclonal antibody with evidence supporting discontinuation once amyloid has been cleared. Over 75% of Kisunla patients in trials reached “minimal” amyloid levels on brain imaging, and the concept of stopping the medication once amyloid burden is sufficiently reduced is unique to Kisunla among approved therapies. This could theoretically reduce long-term treatment burden and costs, though the optimal timing and criteria for discontinuation are still being defined. Leqembi is typically continued long-term; patients in CLARITY AD had a 94% persistence rate when offered an extension study, suggesting strong tolerance and willingness to continue.
What About Side Effects and Amyloid-Related Imaging Abnormalities?
Both drugs carry a risk of amyloid-related imaging abnormalities (ARIA), which are brain changes seen on MRI that reflect the inflammatory process of amyloid clearance. These can appear as microhemorrhages (small brain bleeds) or microinfarcts (small ischemic lesions). Most ARIA cases are asymptomatic and detected only on screening MRI, but some patients experience symptoms such as headaches, confusion, or vision changes. In 2025, the FDA updated Kisunla’s label with new titration dosing specifically designed to reduce ARIA risk, reflecting the agency’s commitment to refining these treatments as real-world use expands.
Serious side effects are uncommon but have been reported. Patients taking these medications require regular cognitive monitoring and MRI screening to detect ARIA early. For patients with cerebral amyloid angiopathy (CAA), a condition where amyloid deposits in blood vessel walls, the risk of ARIA may be higher, though CAA screening is not yet standard before starting these drugs. This is an area where the warning is clear: these medications require medical supervision, regular imaging, and informed consent about the possibility of ARIA, which is why they should only be prescribed and monitored by specialists experienced with anti-amyloid therapies.
Real-World Uptake and Patient Persistence
The clinical trial data showed strong patient adherence to these medications, but real-world adoption tells another story. Of CLARITY AD patients who completed 18 months of Leqembi treatment, 94% chose to continue in the long-term extension study, suggesting that patients who start these therapies tend to persist with them. Real-world data from 2026 shows sustained treatment persistence in U.S.
healthcare systems, though access remains limited by insurance coverage and the requirement for regular IV or subcutaneous infusions. Practical barriers include the infusion schedule—every two to four weeks for months or years—the need for regular MRI screening, cognitive testing, and the cost, even when insurance covers it. Some patients find the commitment manageable; others discontinue due to inconvenience or mild side effects. For families hoping these drugs will restore lost function, the reality of ongoing treatment without cognitive improvement may be disappointing, even though slowing decline is valuable.
What This Means for Someone With Early Alzheimer’s
For someone diagnosed with mild cognitive impairment or mild dementia due to Alzheimer’s disease, Leqembi or Kisunla represent a genuine but limited therapeutic option. These drugs are not a cure and will not restore lost memories. What they offer is approximately a 30–35% slowing of the rate of cognitive decline over time, meaning that someone on these medications may experience slower loss of independence, lower risk of disease progression, and a longer period of time before advancing to more severe stages.
Whether this benefit justifies the time, expense, and risks of treatment is a decision each patient and family must make with their neurologist or geriatrician. The approval of subcutaneous Leqembi in 2026 and the ongoing refinement of Kisunla’s dosing regimen reflect the medical community’s recognition that these drugs address a real need in early Alzheimer’s care. They represent progress in slowing a devastating disease, even if they do not restore what has already been lost. For families seeking memory restoration, the honest answer remains: these medications cannot bring back the grandmother who no longer remembers your name, but they may help preserve the cognitive function that remains and extend the time before decline accelerates further.
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Frequently Asked Questions
If Leqembi and Kisunla clear amyloid plaques from the brain, why don’t they restore memory?
Amyloid plaques are believed to trigger neurodegeneration, but clearing plaques does not bring dead brain cells back to life. These drugs slow future decline rather than reverse past damage.
Who is eligible to take Leqembi or Kisunla?
Both medications are approved only for people in the mild cognitive impairment or mild dementia stages of Alzheimer’s disease, as determined by cognitive testing and amyloid confirmation on PET imaging or CSF testing.
How much slower does cognitive decline actually become on these medications?
Clinical trials show approximately 30–35% slowing of cognitive decline compared to placebo. This translates to measurable but modest differences on standardized cognitive scales over 18–36 months.
What is ARIA and should I be worried about it?
ARIA refers to amyloid-related imaging abnormalities—brain changes seen on MRI during amyloid clearance. Most cases are asymptomatic, but serious ARIA can cause brain microhemorrhages or microinfarcts. Regular MRI screening is required to detect ARIA early.
Can I stop taking these medications once my memory stabilizes?
Leqembi is typically continued long-term. Kisunla has evidence supporting discontinuation once amyloid is sufficiently cleared, making it potentially unique in this regard, though optimal stopping criteria are still being defined.
How long do these drugs take to work, and how long do I need to take them?
Both medications require months of regular infusions before amyloid clearance becomes evident on brain imaging. For Leqembi, long-term treatment is standard; for Kisunla, discontinuation after amyloid clearance is an emerging option. —
