Biogen data sits at the center of this dementia and brain health question.
New data from Eisai and Biogen confirms what healthcare providers have observed in clinical practice: the vast majority of patients with early Alzheimer’s disease choose to stay on Leqembi (lecanemab) long-term. Real-world evidence covering over 10,700 U.S. patients shows that 78.4% remained on treatment at 18 months, with significant continuation rates extending to 24 months. Even more striking, 94% of patients who completed the initial 18-month treatment period in the Phase 3 CLARITY-AD trial voluntarily enrolled in the open-label extension study to continue maintenance therapy.
This persistent engagement with treatment across both clinical trials and routine medical practice suggests something important: when patients experience benefit—or at least see value in continuing—they stay the course with this disease-modifying drug. The data presented March 20, 2026, at the 20th International Conference on Alzheimer’s and Parkinson’s Diseases in Copenhagen represents a significant real-world verification of Leqembi’s long-term role in early Alzheimer’s care. Rather than serving as a one-time intervention, the drug is emerging as a long-term disease management tool that patients and their caregivers actively choose to maintain. This article examines what the data actually shows about patient persistence, the clinical outcomes supporting continued treatment, the safety profile beyond the initial phase, and what these trends mean for people facing an early Alzheimer’s diagnosis.
Table of Contents
- What Do Real-World Persistence Rates Tell Us About Patient Commitment?
- How Do Trial Results from CLARITY-AD Support What Real-World Data Shows?
- What Happens During the Maintenance Phase of Treatment?
- How Do Patient Choice and Tolerability Shape Long-Term Outcomes?
- What Safety Considerations Should Patients Know About Long-Term Treatment?
- How Does Early Detection Impact the Ability to Use Leqembi Long-Term?
- What Does This Data Mean for the Future of Alzheimer’s Care?
- Conclusion
- Frequently Asked Questions
What Do Real-World Persistence Rates Tell Us About Patient Commitment?
The numbers from the PurpleLab CLEAR Claims analysis represent genuine U.S. medical claims data—not controlled trial conditions, but the actual treatment patterns of 10,763 individuals who initiated lecanemab therapy between January 2023 and November 2025. At 18 months, 78.4% had continued treatment. By 20 months, persistence held at 71.7%. At 24 months, 67.3% remained on therapy.
These are not drop-off rates of 10-20% annually; they are rates of sustained engagement with a biweekly infusion protocol that requires traveling to an infusion center, blocking off time from daily life, and managing the logistics of ongoing medical treatment. The mean follow-up period across this patient population was 350.9 days—roughly 11.5 months—with patients receiving infusions at a mean interval of 16.4 days (median 14 days). This consistency in dosing intervals suggests that the treatment schedule itself isn’t driving discontinuation; patients are maintaining a regular appointment pattern even as they track time and manage their disease. Compared to other long-term treatments in neurology and oncology, these persistence rates are high. They indicate that the barrier to continuation—whether that’s effectiveness, tolerability, or patient belief in value—is not substantially preventing ongoing use.
How Do Trial Results from CLARITY-AD Support What Real-World Data Shows?
The CLARITY-AD trial enrolled patients with early symptomatic Alzheimer’s disease—those with mild cognitive impairment or mild dementia stage with confirmed amyloid pathology on biomarker testing. Among these patients, 94% who completed the initial 18-month treatment period chose to enter an open-label long-term extension study. This voluntary transition is significant because patients and their families are making a choice based on their experience with the drug in the controlled trial setting. They had 18 months to assess whether the treatment was providing perceived benefit, whether side effects were manageable, and whether continuing made sense for their situation.
The clinical outcomes that support this patient choice are substantial. In the early Alzheimer’s population with low tau pathology, 73% showed no cognitive decline (measured by Clinical Dementia Rating Scale—Sum of Boxes) at four years, while 61% showed actual cognitive improvement at the same timepoint. These aren’t marginal effects; they represent meaningful preservation or reversal of cognitive function over a multi-year period. However, these benefits apply primarily to patients in the early disease stage with confirmed amyloid positivity—the population eligible for treatment. Patients with moderate to advanced dementia, or those without biomarker-confirmed amyloid pathology, would not show the same benefit trajectory, making early identification and treatment critical.
What Happens During the Maintenance Phase of Treatment?
The leap from the initial 18-month induction period to long-term maintenance reflects an important shift in how Leqembi is being used. Rather than a finite treatment course, the drug is positioned as a chronic therapy—similar to how statins work for cardiovascular disease or antihypertensive medications for blood pressure management. The maintenance phase builds on the amyloid reduction achieved during the first 18 months, with continued biweekly infusions sustaining that effect and theoretically preventing further amyloid accumulation. Safety data from the long-term extension period showed no new adverse findings beyond what was observed in the induction phase.
The majority of side effects—including amyloid-related imaging abnormalities (ARIA), infusion reactions, and other expected events—occurred most frequently in the first 12 months of treatment. This means that patients entering the maintenance phase have already navigated the period of greatest risk and are typically managing a well-characterized safety profile. The durability of this safety profile across two to four years of continuous treatment is what allows the high persistence rates we see in real-world practice. If serious new side effects emerged after 18 months, discontinuation rates would likely spike.
How Do Patient Choice and Tolerability Shape Long-Term Outcomes?
The fact that 78-67% of real-world patients persisted on lecanemab through 24 months tells us something that clinical efficacy studies alone cannot: patients are willing to undergo repeated medical procedures and maintain a disease management regimen when they perceive value. This choice is shaped by multiple factors—not just cognitive outcomes, but the lived experience of managing infusions, managing side effects, and managing expectations around disease progression. In Alzheimer’s disease, where cognitive decline is often profound and treatments have been limited, even slowing decline is experienced as meaningful by many patients and caregivers.
Tolerability emerges as a critical factor in this persistence equation. Leqembi’s side effect profile in clinical practice is generally manageable, with infusion-related reactions being relatively uncommon and ARIA (the amyloid-related imaging abnormalities that sometimes occur with amyloid-targeting drugs) being monitored and managed rather than universally stopping treatment. Patients who experience manageable side effects versus those who experience severe or life-altering adverse events will make different continuation decisions. The high persistence rates suggest that for most patients in the real world, the experienced tolerability supports ongoing treatment.
What Safety Considerations Should Patients Know About Long-Term Treatment?
Amyloid-related imaging abnormalities (ARIA) remain an important consideration in long-term lecanemab use, even though they don’t typically force discontinuation. ARIA can manifest as amyloid-related transient amyloid-related imaging abnormalities (ARIA-T), characterized by edema in the brain, or ARIA-H, characterized by microhemorrhages and microinfarcts. These are monitored through MRI surveillance, typically conducted at baseline, 18 months, and periodically thereafter. While these findings sound alarming, most are asymptomatic and managed through treatment monitoring and continued therapy. However, if ARIA becomes symptomatic or severe, treatment modification or discontinuation may become necessary. This is why ongoing radiologic surveillance is standard practice in Leqembi treatment protocols.
Patients should understand that long-term lecanemab therapy is not a cure—it is a disease-modifying treatment intended to slow cognitive decline in early disease. Some patients remain on treatment and continue to experience gradual cognitive decline, even with therapy. The goal is not to prevent decline entirely but to substantially slow it, providing a longer period of functional independence and cognitive ability. For some patients and families, this is sufficient motivation to continue treatment indefinitely. For others, if decline continues despite therapy, the calculus of whether to continue may shift. The data showing 67% persistence at 24 months also means 33% have discontinued by that point—some due to lack of perceived benefit, some due to side effects, and some due to progression into more advanced disease where the treatment may no longer be indicated.
How Does Early Detection Impact the Ability to Use Leqembi Long-Term?
Access to Leqembi and the ability to benefit from long-term treatment depends critically on early detection—identifying amyloid pathology in cognitively normal individuals or those with very mild cognitive impairment. This requires biomarker testing, either through positron emission tomography (PET) imaging, cerebrospinal fluid analysis, or the newer blood-based biomarkers that measure phosphorylated tau and amyloid-beta ratios. Insurance coverage for these biomarker tests has expanded significantly, but many patients who would benefit from early detection still don’t access this testing because the disease hasn’t been formally suspected or cognitive symptoms haven’t driven a medical evaluation.
Patients and families who engage with cognitive screening, pursue biomarker testing when indicated, and initiate Leqembi in the early disease window are positioned to experience the full benefit trajectory. The 73% showing no cognitive decline at four years were identified early and began treatment while cognitive reserve was still substantial. Earlier initiation of treatment—moving toward truly preclinical use in biomarker-positive cognitively normal individuals—is emerging as the next frontier, and persistence data in this population will be important in understanding whether long-term therapy benefits this less symptomatic group.
What Does This Data Mean for the Future of Alzheimer’s Care?
The sustained persistence rates with Leqembi signal a shift in how neurology and primary care may approach Alzheimer’s disease management. Rather than viewing anti-amyloid therapies as a finite treatment course, the field is increasingly considering them as long-term disease management strategies. This mirrors the evolution of cancer treatment (from single chemotherapy courses to ongoing targeted therapies) and cardiovascular medicine (where statins and blood pressure medications are often lifelong).
The implication is that patients who initiate Leqembi in early disease should anticipate years of continued treatment, ongoing monitoring, and integrated care involving cognitive specialists, imaging radiologists, and primary care providers. Looking forward, the combination of improved blood-based biomarkers, the emergence of oral anti-amyloid compounds, and the continued refinement of lecanemab’s use position the field to treat more patients earlier and potentially with greater convenience. If oral alternatives with similar efficacy emerge and prove to have comparable long-term persistence rates, access to disease modification could expand dramatically. The current data—showing that patients do choose to stay on Leqembi when they begin it—provides evidence that effective, tolerable disease-modifying treatments in Alzheimer’s are sustainable as chronic therapies, not just as temporary interventions.
Conclusion
Eisai and Biogen’s presentation of real-world persistence data demonstrates a fundamental clinical truth: when patients with early Alzheimer’s disease access a disease-modifying treatment like lecanemab that provides tangible benefit with manageable side effects, they choose to continue it. Persistence rates of 78% at 18 months and 67% at 24 months, supported by 94% voluntary enrollment in long-term extension studies, reflect genuine patient engagement with a chronic disease management strategy. These rates exceed many expectations for a treatment requiring regular infusion appointments and ongoing monitoring, suggesting that patients and caregivers view the cognitive benefits—or at minimum, the slowing of decline—as worth the logistical and medical commitment involved.
For people newly diagnosed with early symptomatic Alzheimer’s disease or those discovered to have amyloid pathology on biomarker screening, these findings offer reassurance that beginning Leqembi is not a short-term intervention but the start of a potentially years-long disease modification strategy. The key steps forward involve expanding early detection through broader biomarker screening, ensuring equitable access to both the drug and the MRI surveillance required for safe use, and establishing robust systems for ongoing cognitive and neuroimaging monitoring as patients settle into the maintenance phase of treatment. The data confirms what clinical practice has begun to demonstrate: in early Alzheimer’s disease, effective disease modification is not just possible—it is something patients actively choose to maintain.
Frequently Asked Questions
How long do patients typically stay on Leqembi?
Real-world data shows 78.4% of patients remain on treatment at 18 months, 71.7% at 20 months, and 67.3% at 24 months. Many patients continue for several years, with clinical trial participants transitioning to a maintenance phase designed for long-term therapy.
Is Leqembi a cure for Alzheimer’s disease?
No. Leqembi is a disease-modifying treatment that slows cognitive decline in early Alzheimer’s disease. It reduces amyloid in the brain, but most patients continue to experience some gradual cognitive changes even while on treatment. The goal is to extend the period of cognitive function and independence, not to reverse or prevent all decline.
What are the main side effects patients experience on long-term Leqembi therapy?
The most common side effects occur in the first 12 months and include infusion-related reactions and amyloid-related imaging abnormalities (ARIA). These are typically asymptomatic and managed through monitoring rather than requiring treatment discontinuation. After the first year, the side effect profile remains stable without new concerns emerging.
Do all patients who start Leqembi benefit from long-term treatment?
Not every patient experiences the same degree of benefit. Approximately 73% of patients in the early disease stage with low tau show no cognitive decline at four years, while 61% show improvement. Some patients continue treatment despite ongoing decline, while others discontinue due to lack of perceived benefit or adverse effects.
How often do patients need infusions while on maintenance therapy?
Patients receive lecanemab infusions every 2 weeks on average (mean 16.4 days, with a median of 14 days). This schedule is maintained throughout both the induction and maintenance phases of treatment, requiring ongoing commitment to regular medical appointments.
Are there any tests or monitoring required during long-term Leqembi therapy?
Yes. Brain MRI scans are typically performed at baseline, 18 months, and periodically thereafter to monitor for amyloid-related imaging abnormalities. Cognitive assessments and clinical evaluations are also part of ongoing care to track disease progression and treatment response.
You Might Also Like
- New resources available for caregivers and patients dealing with Dementia
- Lecanemab Safety Confirmed by Research Team in New Study
- Government efforts focus on prevention and research funding
For more, see NIH MedlinePlus — dementia.
