Leqembi (lecanemab) works by targeting and clearing amyloid beta plaques from the brain, the sticky protein clusters believed to drive nerve cell damage in early Alzheimer’s disease. As an Alzheimer’s disease treatment, it is the first therapy shown in clinical trials to meaningfully slow cognitive decline rather than simply manage symptoms. For patients diagnosed with mild cognitive impairment or early-stage Alzheimer’s, this represents a genuine shift in what treatment can accomplish.
This article walks through how Leqembi actually works in the brain, what the research shows about slowing progression, the side effects patients should understand before starting, and how it compares to older Alzheimer’s dementia medications. If you or a family member has recently received an early Alzheimer’s diagnosis, understanding these mechanics can help you have a more informed conversation with your neurologist.
What Makes Leqembi Different From Older Alzheimer’s Medications
For decades, Alzheimer’s dementia medications like donepezil and memantine worked by adjusting brain chemistry to temporarily ease symptoms such as confusion or memory lapses. They never touched the underlying disease process. Leqembi is different because it is a monoclonal antibody designed to go after amyloid beta protein itself, the substance that clumps together and forms plaques between brain cells.
By binding to and helping clear these plaques, Leqembi addresses a root biological driver of Alzheimer’s rather than just masking its effects. This is why it is often described as a disease-modifying treatment, a category that is genuinely new for this condition.
Amyloid Plaques and Why They Matter
Amyloid beta is a normal protein fragment, but in Alzheimer’s disease it misfolds and accumulates into hard plaques. These plaques are thought to trigger inflammation, disrupt communication between neurons, and contribute to the tangles of tau protein that follow. Over time, this cascade damages the connections responsible for memory, reasoning, and daily functioning.
Leqembi specifically targets protofibrils, an early and particularly toxic form of amyloid beta that appears before plaques fully harden. This early intervention point is part of why the treatment shows benefit when started during the mild cognitive impairment or early Alzheimer’s stage, rather than later in the disease.
How Leqembi Slows Alzheimer’s Progression
Leqembi is administered as an intravenous infusion, typically every two weeks. Each infusion delivers antibodies that circulate through the bloodstream, cross into brain tissue, and bind to amyloid protofibrils and plaques. The immune system is then recruited to help clear this material away.
Clinical trial data showed that patients receiving Leqembi experienced a slower rate of decline on standard measures of cognition and daily function compared to those on placebo. It does not reverse damage that has already occurred or cure Alzheimer’s disease, and it does not stop progression entirely. What it does is measurably slow the pace at which memory and function deteriorate over time, which for many families translates into more months or years of independence.
Who Is a Candidate for Leqembi
Leqembi is approved specifically for people with mild cognitive impairment or mild dementia due to Alzheimer’s disease, confirmed through biomarker testing showing the presence of amyloid in the brain. It is not intended for moderate or advanced Alzheimer’s, and it is not a treatment for other forms of dementia unrelated to amyloid pathology.
Before starting treatment, candidates typically undergo:
- Cognitive testing to confirm the stage of impairment
- Brain imaging (PET scan or cerebrospinal fluid analysis) to confirm amyloid presence
- Genetic testing for the APOE4 gene, which affects side effect risk
- Baseline MRI to screen for any existing brain abnormalities
A thorough diagnostic workup matters here because Leqembi is only appropriate for a specific window in the disease timeline. Our clinic’s Leqembi treatment program includes this evaluation process to determine candidacy before any infusions begin.
Leqembi Side Effects Patients Should Understand
Like any disease-modifying therapy, Leqembi carries risks that need to be weighed carefully alongside its benefits. Understanding these upfront helps patients and families make a fully informed decision rather than being surprised partway through treatment.
Common and Mild Side Effects
- Infusion-related reactions such as fever, chills, or nausea during or shortly after the infusion
- Headache
- Fatigue
These reactions tend to occur most often with the first few infusions and are usually manageable with monitoring and, when needed, pre-treatment with antihistamines or other supportive medication.
ARIA: The Side Effect That Requires Close Monitoring
The most significant Leqembi side effects to be aware of fall under a category called ARIA, or amyloid-related imaging abnormalities. ARIA can appear as either:
- ARIA-E: temporary swelling in areas of the brain
- ARIA-H: small spots of bleeding or hemosiderin deposits in brain tissue
Many cases of ARIA cause no noticeable symptoms and are detected only through routine MRI monitoring, which is why scheduled scans are a required part of treatment. When symptoms do occur, they can include headache, confusion, dizziness, or vision changes, and in rare cases more serious complications. Patients who carry two copies of the APOE4 gene face a higher risk of ARIA, which is a key reason genetic testing is part of the pre-treatment workup.
Because of this risk profile, ongoing neurological monitoring throughout treatment is essential, not optional. This is also where complementary diagnostic tools matter: many patients undergoing amyloid-targeting therapy benefit from periodic Transcranial Doppler (TCD) evaluation or EEG testing as part of a broader neurological picture, particularly if new symptoms arise between scheduled MRIs.
Leqembi Compared to Traditional Alzheimer’s Dementia Medications
It helps to see how Leqembi fits alongside the medications that have been standard for years. Both categories can play a role, and in some cases are used together as part of a broader treatment plan.
| Feature | Leqembi (Lecanemab) | Traditional Medications (Donepezil, Memantine, etc.) |
|---|---|---|
| Mechanism | Clears amyloid protofibrils and plaques from the brain | Adjusts neurotransmitter levels to ease symptoms |
| Effect on disease course | Slows underlying progression | Does not alter disease progression |
| Administration | IV infusion every two weeks | Daily oral tablet |
| Monitoring required | Regular MRI scans, genetic testing, infusion observation | Periodic clinical check-ins |
| Eligible stage | Mild cognitive impairment or early Alzheimer’s only | Broader range, including moderate to severe stages |
Many patients are not choosing one over the other but combining approaches under a neurologist’s guidance to address both the biological disease process and day-to-day symptom management.
What the Treatment Process Actually Looks Like
Understanding the practical rhythm of Leqembi treatment helps set realistic expectations. This isn’t a one-time procedure but an ongoing commitment that requires coordination between imaging, infusion visits, and neurological follow-up.
Before Starting
- Comprehensive memory and cognitive evaluation
- Amyloid confirmation through PET imaging or spinal fluid testing
- APOE4 genetic testing
- Baseline brain MRI
During Treatment
- IV infusions typically every two weeks, each lasting about an hour
- Observation period after each infusion to watch for reactions
- Periodic MRI scans to screen for ARIA, especially in the earlier months of treatment
- Ongoing cognitive reassessment to track response over time
Some patients also benefit from supportive therapies alongside Leqembi, such as multivitamin and specialty infusions to support overall neurological health, though these are complementary rather than a substitute for amyloid-targeting treatment. A neurologist can help determine what combination makes sense for an individual’s diagnosis and overall health.
Why Early Diagnosis Matters So Much With This Treatment
Leqembi’s approval is narrowly defined to the mild cognitive impairment and early Alzheimer’s stage for a reason: the clinical evidence for benefit is strongest when amyloid clearance begins before extensive neuronal damage has occurred. Waiting until symptoms are more advanced significantly narrows the window in which this treatment can help.
This is precisely why proactive evaluation matters when memory changes first appear, whether that’s increased forgetfulness, difficulty with familiar tasks, or word-finding trouble. Diagnostic tools such as brain mapping and cognitive testing can help distinguish early Alzheimer’s from other causes of memory change, some of which are treatable or reversible entirely. Getting an accurate diagnosis early isn’t just about starting Leqembi sooner, it’s about making sure the treatment plan actually matches what’s happening in the brain.
Talking It Through With a Neurologist
Because Leqembi involves real risks, meaningful monitoring requirements, and a narrow window of eligibility, the decision to start treatment should always be made in close consultation with a neurologist familiar with amyloid-targeting therapies. Questions worth raising during that conversation include how ARIA risk applies to your specific genetic profile, what the realistic expectations are for slowing decline, and how Leqembi might fit alongside any other medications already in use.
Patients in Brooklyn and the surrounding areas considering this path can find more detail on eligibility and the evaluation process on our Leqembi treatment page, which outlines what the diagnostic workup and infusion schedule involve at our clinic.
Alzheimer’s disease treatment has entered a genuinely new chapter with amyloid-targeting therapies like Leqembi, and understanding how it works, what it can realistically offer, and what it requires in terms of monitoring puts patients and families in a much stronger position to make the right decision for their situation. If you’re noticing early memory changes in yourself or a loved one, an honest, thorough evaluation is the best next step before any treatment decision is made. Our team at Apex Neurology is available to walk through that evaluation process, answer questions about candidacy, and help build a plan that fits your specific diagnosis. You can also find more patient experiences and clinic details on our Google Business Profile when you’re ready to take that next step.
