Lecanemab, sold under the brand name Leqembi, is the anti-amyloid immunotherapy that has been working so well in clinical practice that it is steadily pushing the older drug aducanumab — marketed as Aduhelm — toward obsolescence. Since Leqembi received full traditional approval from the FDA in 2023, its clearer efficacy data and broader insurance coverage have made Aduhelm increasingly difficult to justify prescribing. Biogen, the company behind Aduhelm, effectively pulled the drug from the market, announcing it would discontinue sales to focus resources elsewhere. For families navigating a new Alzheimer’s diagnosis, this shift represents something rare in dementia care: one treatment clearly outperforming another in head-to-head relevance, even if neither drug is a cure. This is not a story of a miracle drug replacing a failed one.
Aduhelm was never proven to be ineffective at clearing amyloid plaques — it did that reasonably well. The problem was that its clinical trial data never convincingly demonstrated that clearing those plaques translated into meaningful cognitive benefits for patients. Leqembi, by contrast, showed a statistically significant slowing of cognitive decline in its confirmatory Phase 3 trial, known as CLARITY AD. The difference was modest — roughly 27 percent less decline over 18 months compared to placebo — but it was real and measurable, and that was enough to change the calculus for neurologists, insurers, and regulators. This article examines how this shift happened, what it means for patients today, the risks that come with these drugs, and what the next generation of Alzheimer’s treatments may look like.
Table of Contents
- Why Is Leqembi Replacing Aduhelm in Alzheimer’s Treatment?
- How Effective Is Leqembi, and What Are Its Limitations?
- What Happened to Aduhelm and Why Did It Fail Commercially?
- Who Should Consider Leqembi and Who Should Not?
- The ARIA Problem — Understanding the Most Serious Side Effect
- Blood Tests May Change Who Gets Diagnosed and Treated
- What Comes After Leqembi — Donanemab and the Next Wave
- Conclusion
- Frequently Asked Questions
Why Is Leqembi Replacing Aduhelm in Alzheimer’s Treatment?
The simplest answer is evidence. When the FDA granted Aduhelm accelerated approval in June 2021, the decision was immediately controversial. One of Biogen’s two pivotal trials had been stopped early for apparent futility, and the other showed benefits only after a post-hoc analysis of a subset of patients who received the highest dose. The FDA’s own advisory committee voted nearly unanimously against approval, and several members resigned in protest after the agency approved it anyway. Medicare initially refused to cover Aduhelm broadly, restricting reimbursement to patients enrolled in approved clinical trials — a near-unprecedented move that effectively crippled the drug‘s commercial viability. Leqembi entered a very different landscape.
Its Phase 3 CLARITY AD trial enrolled nearly 1,800 participants with early-stage Alzheimer’s and mild cognitive impairment due to Alzheimer’s pathology. The results, published in the New England Journal of Medicine, showed the drug slowed clinical decline on a standard dementia rating scale by 27 percent relative to placebo over 18 months. That margin was not dramatic in everyday terms — families would be unlikely to notice a stark difference — but it met the threshold regulators and clinicians had been waiting for: proof that removing amyloid from the brain actually changes the disease trajectory, even modestly. The contrast mattered enormously for insurance coverage. After Leqembi’s traditional approval, Medicare agreed to cover the drug for eligible patients, opening the door for hundreds of thousands of Americans. Aduhelm, still hamstrung by its coverage restrictions and tainted reputation, could not compete. Biogen announced in early 2024 that it would discontinue Aduhelm, not because the drug stopped working mechanically, but because the market and the medical community had moved on.
How Effective Is Leqembi, and What Are Its Limitations?
It is important to be precise about what “working so well” actually means in this context. Leqembi does not reverse Alzheimer’s disease. It does not restore lost memories or return patients to their prior cognitive baseline. What it does, based on clinical trial data, is slow the rate of decline — buying time, not turning back the clock. On the Clinical Dementia Rating-Sum of Boxes scale, the difference between the Leqembi group and the placebo group amounted to less than half a point over 18 months. For some patients and families, that margin may represent meaningful additional months of independence. For others, particularly those hoping for a more dramatic intervention, the benefit may feel negligible. However, if a patient is already in moderate or advanced stages of Alzheimer’s, Leqembi is not indicated and has not been shown to help.
The clinical trials enrolled only individuals with early symptomatic disease who had confirmed amyloid pathology via PET scan or cerebrospinal fluid testing. This is a critical limitation: the drug requires a confirmed diagnosis at a stage when many patients have not yet been formally evaluated, and the diagnostic workup itself — including amyloid PET imaging — can be expensive and not universally accessible. Rural communities and underserved populations face particular barriers to meeting the eligibility criteria. There is also the matter of side effects. Amyloid-related imaging abnormalities, known as ARIA, are the most significant safety concern. ARIA can manifest as brain swelling (ARIA-E) or microbleeds (ARIA-H). In the CLARITY AD trial, roughly 13 percent of Leqembi-treated patients experienced ARIA-E, though most cases were asymptomatic and detected only on routine MRI monitoring. A small number of serious cases, including several deaths in patients who were on blood thinners, have underscored the need for careful patient selection and regular imaging surveillance.
What Happened to Aduhelm and Why Did It Fail Commercially?
Aduhelm’s story is a cautionary tale about what happens when regulatory optimism outpaces clinical evidence. When Biogen priced the drug at $56,000 per year at launch — later reduced to $28,200 after widespread backlash — it was asking patients, insurers, and the health system to pay a premium for a drug whose benefit was genuinely uncertain. The FDA’s decision to use the accelerated approval pathway, which allows drugs to be approved based on a surrogate endpoint like amyloid clearance rather than proven clinical benefit, set the stage for every problem that followed. The backlash was swift and multidirectional. Major medical centers, including the Cleveland Clinic, initially declined to administer the drug. Three members of the FDA’s advisory committee resigned.
Congressional investigations examined the relationship between Biogen and the FDA during the review process, raising questions about an unusually close collaboration. Meanwhile, practically no one was receiving the drug: by the time Medicare finalized its restrictive coverage decision in 2022, Aduhelm’s commercial prospects were essentially dead. Biogen reported minimal revenue from the product, and the company’s stock price reflected the market’s verdict. The real damage may have been reputational. Aduhelm’s troubled approval process made regulators, physicians, and the public more skeptical of the amyloid hypothesis — the foundational theory that removing amyloid plaques from the brain should improve Alzheimer’s outcomes. Ironically, Leqembi’s later success provided the very evidence that Aduhelm could not deliver, partially rehabilitating the amyloid approach in the eyes of many researchers, even as debate continues about whether amyloid clearance alone is sufficient to meaningfully alter the disease.
Who Should Consider Leqembi and Who Should Not?
The clearest candidates for Leqembi treatment are individuals with early symptomatic Alzheimer’s disease — typically those with mild cognitive impairment or mild dementia — who have biomarker confirmation of amyloid pathology. This confirmation usually requires either a PET scan or a lumbar puncture for cerebrospinal fluid analysis, though blood-based biomarker tests are rapidly emerging and may simplify this process in the near future. Patients who carry two copies of the APOE4 gene — the strongest known genetic risk factor for late-onset Alzheimer’s — face a more complicated decision. In the CLARITY AD trial, APOE4 homozygotes had significantly higher rates of ARIA, including more severe cases. Some clinicians have adopted a more cautious approach with these patients, weighing the elevated risk against the modest expected benefit.
The prescribing information does not outright contraindicate Leqembi for APOE4 homozygotes, but the conversation between doctor and patient becomes considerably more nuanced. The tradeoff calculus also involves logistics and cost. Leqembi is administered as an intravenous infusion every two weeks, requiring regular visits to an infusion center. Patients must also undergo periodic MRI scans to monitor for ARIA, adding further time and expense. As of recent reports, the list price has been approximately $26,500 per year, though out-of-pocket costs vary depending on insurance coverage. For patients weighing whether the modest cognitive benefit justifies the time commitment, potential side effects, and financial burden, there is no universally correct answer — it depends heavily on individual circumstances, values, and disease stage.
The ARIA Problem — Understanding the Most Serious Side Effect
ARIA remains the central safety concern for all anti-amyloid immunotherapies, not just Leqembi. The term covers two related but distinct phenomena: ARIA-E, which involves fluid accumulation or edema in the brain, and ARIA-H, which involves small hemorrhages or superficial siderosis. Both are detected on MRI, and many cases produce no noticeable symptoms. However, symptomatic ARIA can present as headache, confusion, dizziness, visual disturbances, or nausea, and in rare cases it can be serious or life-threatening. The risk is not evenly distributed. Patients taking anticoagulant medications appear to face substantially higher danger.
Several deaths reported during Leqembi’s clinical development and early post-marketing use involved patients on blood thinners, raising urgent questions about drug interactions. Current clinical guidance generally advises extreme caution — or avoidance — when considering Leqembi for patients on anticoagulation therapy, though formal contraindications may evolve as more real-world data accumulates. Monitoring protocols require MRI scans before treatment initiation and at regular intervals during therapy, typically before the fifth, seventh, and fourteenth infusions at minimum. If ARIA is detected, treatment is usually paused until the findings resolve. This monitoring requirement places a significant burden on both patients and the healthcare system, particularly in regions where MRI access is limited. It also means that patients who cannot reliably attend follow-up imaging appointments may not be appropriate candidates, regardless of their disease stage.
Blood Tests May Change Who Gets Diagnosed and Treated
One of the most significant developments adjacent to the Leqembi story is the rapid advancement of blood-based biomarker tests for Alzheimer’s pathology. Historically, confirming the presence of amyloid plaques required either a PET scan costing several thousand dollars or an invasive lumbar puncture. Blood tests measuring phosphorylated tau and amyloid ratios have shown promising accuracy in research settings and are beginning to enter clinical use.
If these tests become widely available and reliable, they could dramatically expand the pool of patients eligible for treatment. A primary care physician could order a blood draw rather than referring a patient to a specialized imaging center, collapsing a diagnostic journey that currently takes months into a matter of weeks. However, the tests are not yet considered fully validated for routine clinical decision-making as of the most recent available data, and false positive or negative results remain a concern. The intersection of cheaper diagnostics and available treatment could reshape early Alzheimer’s care — but that transformation is still unfolding.
What Comes After Leqembi — Donanemab and the Next Wave
Leqembi is not the end of this story. Donanemab, developed by Eli Lilly and marketed as Kisunla, represents the next iteration of anti-amyloid therapy. In its Phase 3 TRAILBLAZER-ALZ 2 trial, donanemab showed a 35 percent slowing of clinical decline in the overall population — a numerically larger effect than Leqembi demonstrated, though direct comparisons between trials are methodologically unreliable. Donanemab also has a potential practical advantage: it is designed as a time-limited treatment.
Once amyloid plaques are cleared to a sufficient degree, dosing can stop, unlike Leqembi’s ongoing biweekly infusions. Looking further ahead, the field is moving toward combination approaches that target multiple aspects of Alzheimer’s pathology — amyloid, tau, inflammation, and metabolic dysfunction — rather than amyloid alone. The modest benefits seen with current monotherapies suggest that amyloid clearance is necessary but not sufficient for robust clinical improvement. For patients and families watching this space, the honest message is one of cautious momentum: the era of treating Alzheimer’s as untreatable is ending, but the era of truly effective treatment has not yet fully arrived.
Conclusion
The displacement of Aduhelm by Leqembi marks a genuine turning point in Alzheimer’s therapeutics, though not the dramatic breakthrough that headlines sometimes suggest. What it demonstrates is that the medical and regulatory system can, eventually, distinguish between a drug with ambiguous evidence and one with clearer proof of benefit. Leqembi works — modestly — and that modest efficacy, combined with insurance coverage and a more straightforward regulatory path, was enough to make Aduhelm unsustainable.
For families facing an Alzheimer’s diagnosis today, the practical takeaway is to have an early and frank conversation with a neurologist about eligibility, expectations, and risks. The benefit of current treatments is real but limited, the side effects are manageable but not trivial, and the diagnostic requirements remain a barrier for many. Staying informed as blood-based biomarkers and newer drugs like donanemab enter the picture will be important, but the most valuable thing any patient can do right now is seek evaluation early, when the available treatments have the best chance of making a difference.
Frequently Asked Questions
Does Leqembi cure Alzheimer’s disease?
No. Leqembi slows the rate of cognitive decline but does not stop or reverse the disease. In clinical trials, patients receiving the drug still experienced worsening symptoms — just at a slower pace than those on placebo.
Is Aduhelm still available?
Biogen announced it would discontinue Aduhelm to redirect resources. As of the most recent reports, the drug was being phased out. Patients previously on Aduhelm should discuss alternative options with their neurologist.
How much does Leqembi cost?
The list price has been reported at approximately $26,500 per year, though actual out-of-pocket costs depend on insurance coverage. Medicare covers Leqembi for eligible patients following its traditional FDA approval.
Who is eligible for Leqembi treatment?
Eligible patients generally have early symptomatic Alzheimer’s disease — mild cognitive impairment or mild dementia — with confirmed amyloid pathology via PET scan, cerebrospinal fluid testing, or potentially emerging blood-based biomarkers.
What is ARIA and how dangerous is it?
ARIA refers to amyloid-related imaging abnormalities, including brain swelling and microbleeds. Most cases are asymptomatic and detected on routine MRI, but serious cases can occur, particularly in patients taking blood thinners or those with two copies of the APOE4 gene.
How does donanemab compare to Leqembi?
Donanemab showed a numerically larger effect in its Phase 3 trial and may offer the advantage of time-limited dosing. However, direct comparisons between different trials are unreliable, and both drugs carry similar ARIA risks.
