Lecanemab (Leqembi) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Lecanemab (brand name Leqembi) is a humanized monoclonal antibody therapy developed by Eisai and BioArctic/Biogen for the treatment of Alzheimer's disease. It represents the first anti-amyloid antibody to receive full approval from the U.S. Food and Drug Administration (FDA) for the treatment of Alzheimer's Disease, marking a historic milestone in disease-modifying therapy (van Dyck et al., 2023; FDA, 2023). 1
Lecanemab received accelerated FDA approval in January 2023 and full traditional approval in July 2023 based on the CLARITY-AD phase 3 trial. It targets soluble amyloid-beta protofibrils, which are believed to be among the most neurotoxic forms of amyloid aggregates. By clearing these pathogenic species, lecanemab slows the progression of cognitive decline in individuals with early-stage Alzheimer's Disease (Swanson et al., 2021). As of 2025, lecanemab has been approved in 53 countries and regions including the United States, Japan, the European Union, China, South Korea, the United Kingdom, Taiwan, and Saudi Arabia. 2
Lecanemab specifically binds to soluble amyloid-beta protofibrils, which are intermediate aggregation species between monomers and mature insoluble plaques. These protofibrils are (Bhatt et al., 2007): 3
- Highly neurotoxic and synaptotoxic, causing direct damage to synapses and neuronal membranes
- Primary drivers of synaptic dysfunction and long-term potentiation impairment
- Precursors that seed further amyloid aggregation and plaque formation
- Soluble species capable of diffusing through brain parenchyma, affecting distant synapses
- Present early in the disease process, often before dense plaque deposition 4
¶ Antibody Properties
| Property |
Detail |
| Target |
Soluble amyloid-beta protofibrils (Aβ 1-42 and Abeta 1-40) |
| Antibody type |
Humanized IgG1 (from murine mAb158) |
| Binding affinity |
High-affinity to protofibrils (KD ~10-100 pM); 1000-fold selectivity for protofibrils over monomers |
| IV administration |
10 mg/kg every 2 weeks (induction and maintenance) |
| SC administration |
360 mg weekly (maintenance via autoinjector, approved August 2025) |
Lecanemab removes amyloid through several pathways (Bhatt et al., 2018): 6
- Microglial phagocytosis: Fc-gamma receptor-mediated activation of microglia:
- Dose-dependent reduction in amyloid PET standardized uptake value ratio (SUVR)
- Acceptable safety profile at doses up to 15 mg/kg
- Linear pharmacokinetics with a half-life of approximately 7 days
- Target engagement confirmed by CSF biomarker changes (reduction in CSF Abeta42/40 ratio) 8
The Bayesian adaptive proof-of-concept Study 201 demonstrated (Swanson et al., 2019):
- 64% reduction in brain amyloid at 12 months at the highest dose (10 mg/kg biweekly)
- 26% slowing of clinical decline on ADCOMS at 12 months
- Dose-dependent clinical effects across all arms
- Signal for reduced rate of brain atrophy on volumetric MRI 9
The pivotal CLARITY-AD randomized, double-blind, placebo-controlled phase 3 trial enrolled 1,795 participants with early Alzheimer's Disease (MCI or mild dementia with confirmed amyloid pathology) (van Dyck et al., 2023): 10
Primary Endpoint: 27% slowing of clinical decline on CDR-SB at 18 months
- Placebo: +1.66 points
- Lecanemab: +1.21 points
- Difference: -0.45 points (p<0.001) 11
Key Secondary Endpoints:
| Measure |
Slowing vs. Placebo |
| ADAS-Cog14 |
26% |
| ADCOMS |
24% |
| ADCS MCI-ADL |
37% |
| amyloid PET (Centiloids) |
-55.5 vs +4.7 |
Biomarker Effects:
- Robust amyloid plaque clearance (~70% at 18 months)
- Reduced tau]] accumulation on PET imaging
- Slowed increase in plasma [pTau217]
- Favorable changes in CSF neurodegenerative biomarkers 13
Benefits were consistently observed across prespecified subgroups (Irizarry et al., 2023):
-
APOE4(): 14
-
Lecanemab-treated participants continued to accrue benefit through 48 months across clinical endpoints
-
Former placebo participants who switched to lecanemab showed catch-up improvement but did not fully close the gap, supporting early intervention
-
After the first 6 months of treatment, ARIA rates were low and similar to placebo rates
-
No association between ARIA occurrence and accelerated long-term clinical progression
-
In the low/no baseline tau subgroup, particularly high rates of clinical stability were observed at 48 months: 69% with no decline on CDR-SB and 56% showing improvement 15
Biomarker Trajectory: Continuous treatment slowed the rate of increase in plasma pTau217 and CSF MTBR-tau243, demonstrating sustained drug effect on both amyloid and tau] pathology cascades. Amyloid pathway biomarkers improved within 3 months and were maintained with continuous treatment. 16
[ARIA] is a class of imaging findings associated with anti-amyloid antibodies, reflecting changes in brain vasculature and cerebral amyloid angiopathy: 17
- ARIA-E (edema): Hyperintense signal on FLAIR MRI, representing vasogenic edema or sulcal effusions
- ARIA-H (hemorrhage): Hypointense foci on SWI/GRE MRI, representing microhemorrhages or superficial siderosis
In the CLARITY-AD trial (Honig et al., 2023):
| Finding |
Lecanemab |
Placebo |
| ARIA-E |
12.6% |
1.7% |
| ARIA-H (microhemorrhages) |
17.3% |
9.0% |
| Symptomatic ARIA |
2.8% |
- |
| Serious ARIA |
<1% |
- |
Most ARIA events were:
- Detected on routine monitoring MRI (majority asymptomatic)
- Mild in severity and self-resolving
- Managed with temporary dosing interruptions
- More frequent in [APOE4( genotyping to inform risk discussion
- Dose interruption for symptomatic ARIA or significant radiographic changes
- Restart at same dose after ARIA resolution confirmed on follow-up MRI
- Permanent discontinuation for severe or recurrent ARIA
Use of anticoagulants increases the risk of ARIA-H and intracerebral hemorrhage. The prescribing information includes warnings about concomitant anticoagulant use, and careful risk-benefit assessment is required for patients requiring anticoagulation therapy.
| Adverse Event |
Lecanemab |
Placebo |
| Infusion-related reactions |
26.4% |
7.4% |
| ARIA-E |
12.6% |
1.7% |
| ARIA-H |
17.3% |
9.0% |
| Headache |
14.0% |
10.2% |
- Typically mild to moderate and most frequent during first 3 infusions
- Symptoms: chills, fever, headache, nausea, flushing, hypotension, arthralgia
- Management: premedication (acetaminophen, diphenhydramine, corticosteroids), slower infusion rate
- IRR incidence decreases substantially after the initial infusions
- No treatment-related deaths were attributed to lecanemab in the CLARITY-AD trial
- Post-marketing surveillance has identified rare fatal cases of ARIA, particularly in patients on anticoagulants or with cerebral amyloid angiopathy
- Careful patient selection and monitoring are essential for minimizing risk
A major advancement in lecanemab's clinical utility came with the FDA approval of Leqembi IQLIK (subcutaneous autoinjector) for maintenance dosing in August 2025:
- Device: Prefilled autoinjector containing 360 mg/1.8 mL (200 mg/mL concentration)
- Administration: Subcutaneous injection completed in approximately 15 seconds
- Dosing: 360 mg weekly (replacing 10 mg/kg IV every 2 weeks after induction phase)
- Self-administration: Can be administered at home by patients or caregivers after training
- Launched: October 6, 2025 in the United States
- Eliminates need for biweekly infusion center visits (reducing time burden from ~1 hour per visit)
- Enables home administration, improving patient convenience and adherence
- Reduces healthcare resource utilization
- Maintains comparable efficacy and safety to IV formulation
- Facilitates long-term treatment sustainability
In January 2026, the FDA accepted for priority review Eisai's supplemental BLA for lecanemab SC autoinjector as a weekly starting dose (eliminating the need for initial IV induction), with a decision expected in 2026.
Lecanemab is indicated for treatment of adults with:
- Early disease stage (CDR global 0.5 or 1.0)
- Confirmed amyloid positivity via PET or CSF
- Ability to comply with treatment schedule and MRI monitoring
- Absence of significant anticoagulation therapy
- Awareness of ARIA risk, particularly for [APOE4( genotyping (to inform ARIA risk discussion)
- Assessment of anticoagulation status
| Feature |
Lecanemab |
donanemab |
Aducanumab |
| Target |
Soluble Abeta protofibrils |
N-truncated Abeta (pyroglutamate-Abeta3-42 in plaques) |
Aggregated Abeta (fibrils and plaques) |
| IV dosing |
10 mg/kg q2w |
Titration to 1400 mg q4w |
10 mg/kg q4w |
| SC option |
Yes (360 mg weekly, approved 2025) |
Not available |
Not available |
| Plaque reduction |
~70% at 18 months |
~80% at 12 months |
~60% at 18 months |
| Clinical slowing (CDR-SB) |
27% |
22-36% (iADRS: 35%) |
~22% (debated) |
| ARIA-E rate |
12.6% |
24.0% |
35.2% |
| Treatment duration |
Continuous |
Time-limited (stop when amyloid cleared) |
Continuous |
| FDA status |
Full approval (July 2023) |
Full approval (July 2024) |
Withdrawn (2024) |
| Global approvals |
53 countries |
Limited |
Withdrawn |
The [DIAN]-TU-001 NexGen trial is evaluating the combination of lecanemab with the anti-tau antibody E2814 (etalanetug) in individuals with dominantly inherited Alzheimer's disease. Initial results demonstrate:
- Feasibility of combination amyloid + tau targeting
- Impact of 6-month lecanemab treatment on amyloid PET with acceptable safety
- Proof-of-concept for addressing both key pathological hallmarks of AD simultaneously
This combination approach reflects the growing consensus that targeting multiple pathways may yield greater clinical benefit than monotherapy, given the complex biology of Alzheimer's Disease involving amyloid-beta plaques, tau] tangles, neuroinflammation, and synaptic dysfunction.
¶ Cost, Access, and Health Economics
- Annual cost: Approximately $26,500 in the United States (reduced from initial $26,500 in 2023)
- Global pricing: Varies by country and payer agreements
- Medicare: Covered under Part B (effective January 2024 after traditional approval)
- Commercial insurance: Coverage expanding but variable
- Patient assistance programs: Manufacturer copay assistance and patient support programs available
- Requirement for amyloid confirmation (PET or CSF) creates bottlenecks
- Need for infusion centers and MRI monitoring infrastructure
- Geographic disparities in access to specialized memory centers
- Health equity concerns regarding underrepresentation of diverse populations in clinical trials
Post-approval real-world data from clinical practice shows:
- ARIA rates consistent with clinical trial experience
- Importance of rigorous patient selection and MRI monitoring
- Practical challenges including infusion scheduling, insurance authorization, and patient education
- Growing experience with diverse patient populations beyond clinical trial eligibility criteria
- Transition to subcutaneous formulation improving treatment adherence and sustainability
Lecanemab represents a watershed achievement in Alzheimer's disease treatment as the first anti-amyloid therapy to demonstrate consistent, clinically meaningful slowing of cognitive decline in a confirmatory phase 3 trial. The 27% slowing of progression on CDR-SB, combined with robust amyloid clearance and favorable effects on downstream biomarkers including tau], supports the amyloid cascade hypothesis and validates decades of research. Long-term extension data through 48 months demonstrate sustained and expanding benefit with continuous treatment. The introduction of the subcutaneous autoinjector formulation in 2025 represents a major practical advance for patients and caregivers. While challenges remain in patient selection, ARIA management, access, and affordability, lecanemab has opened a new era of disease-modifying therapy for Alzheimer's Disease.
- U.S. FDA. FDA approves Leqembi for treatment of Alzheimer's Disease. July 2023. [FDA Announcementhttps://www.fda.gov/drugs/news-events-human-drug-alerts/fda-approves-leqembi-treatment-alzheimers-disease
- Swanson CJ, et al. Anti-amyloid antibodies for Alzheimer's Disease. Nat Rev Neurol. 2023;19:130-144. [doi:10.1038/s41582-022-00764-6https://pubmed.ncbi.nlm.nih.gov/36750888/
- Swanson CJ, et al. Lecanemab mechanism of action. Alzheimers Res Ther. 2021;13:80. [doi:10.1186/s13195-021-00813-8https://pubmed.ncbi.nlm.nih.gov/35236457/
- [Bhatt S, et al. Abeta protofibrils as therapeutic target. J Neurosci. 2007;27(3]:652-659. [doi:10.1523/JNEUROSCI.4849-06.2007]https://pubmed.ncbi.nlm.nih.gov/17409224/)
- Bhatt S, et al. Antibody-mediated plaque clearance mechanisms. Nat Neurosci. 2018;21:306-316. [doi:10.1038/s41593-017-0056-zhttps://pubmed.ncbi.nlm.nih.gov/29379214/
- Satlin A, et al. Lecanemab phase 1 dose-escalation study. Alzheimers Dement. 2018;4:544-555. [doi:10.1016/j.trci.2018.08.007https://pubmed.ncbi.nlm.nih.gov/29524867/
- [Swanson CJ, et al. Lecanemab phase 2b study (Study 201]. Alzheimers Res Ther. 2019;11:68. [doi:10.1186/s13195-019-0519-x]https://pubmed.ncbi.nlm.nih.gov/31152080/)
- [Irizarry MC, et al. APOE4 and lecanemab efficacy and safety in CLARITY-AD. Neurology. 2023;101(16]:e1595-e1607. [doi:10.1212/WNL.0000000000207757]https://pubmed.ncbi.nlm.nih.gov/37498762/)
- [Honig LS, et al. ARIA with lecanemab in CLARITY-AD. Neurology. 2023;101(14]:e1384-e1396. [doi:10.1212/WNL.0000000000207777]https://pubmed.ncbi.nlm.nih.gov/36750891/)
- Dyck CH, et al. Long-term safety and efficacy of lecanemab: results from the CLARITY AD open-label extension study. Alzheimers Dement. 2025;21:e70905. [doi:10.1002/alz.70905https://pubmed.ncbi.nlm.nih.gov/41355080/
- Eisai. AAIC 2025: Four-year efficacy and safety data on continuous treatment with lecanemab. July 2025. [Press Releasehttps://media-us.eisai.com/2025-07-21-EISAI-TO-PRESENT-FOUR-YEAR-EFFICACY-AND-SAFETY-DATA-ON-CONTINUOUS-TREATMENT-WITH-LECANEMAB-AT-THE-ALZHEIMERS-ASSOCIATION-INTERNATIONAL-CONFERENCE-2025
- Eisai. CTAD 2025: New data on continued and expanding benefit of LEQEMBI maintenance treatment. December 2025. [Press Releasehttps://www.eisai.com/news/2025/news202585.html
- [Eisai. FDA approves LEQEMBI IQLIK (lecanemab-irmb] subcutaneous injection for maintenance dosing. August 2025. [Press Release]https://www.eisai.com/news/2025/news202559.html)
- Lecanemab safety in early Alzheimer's Disease. Alzheimers Dement. 2023. [PMID:37253418https://pubmed.ncbi.nlm.nih.gov/37253418/
- Anti-amyloid therapy comparison. J Alzheimers Dis. 2023. [PMID:36628942https://pubmed.ncbi.nlm.nih.gov/36628942/
- BioArctic. Latest data at AAIC 2025 reinforces lecanemab clinical effect. July 2025. [Reporthttps://www.bioarctic.com/en/latest-data-presented-at-aaic-2025-reinforces-lecanemabs-clinical-effect-with-consistent-safety-profile/
The study of Lecanemab (Leqembi) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- van Dyck CH et al., Lecanemab in Early Alzheimer's Disease (2023)
- Cummings J et al., Lecanemab: Appropriate Use Recommendations (2023)
- Zhang J et al., Recent advances in Alzheimer's Disease: Mechanisms, clinical trials and new drug development strategies (2024)
- Honig LS et al., Updated safety results from phase 3 lecanemab study in early Alzheimer's Disease (2024)
- Jucker M, Walker LC, Alzheimer's Disease: From immunotherapy to immunoprevention (2023)
- Terao I, Kodama W, Comparative efficacy, tolerability and acceptability of donanemab, lecanemab, aducanumab and lithium on cognitive function in mild cognitive impairment and Alzheimer's Disease: A systematic review and network meta-analysis (2024)
- Swanson CJ et al., A randomized, double-blind, phase 2b proof-of-concept clinical trial in early Alzheimer's Disease with lecanemab, an anti-Aβ protofibril antibody (2021)
- Cummings J et al., Anti-Amyloid Monoclonal Antibodies for the Treatment of Alzheimer's Disease (2024)