European regulators sits at the center of this dementia and brain health question.

European regulatory authorities requested additional safety data before granting final approval to lecanemab (marketed as Leqembi), a breakthrough Alzheimer’s treatment that represents the first disease-modifying therapy to reach the European market. In April 2025, the European Commission ultimately approved lecanemab after the European Medicines Agency (EMA) provided a positive opinion in November 2024, but the approval came with a significant condition: regulators wanted to evaluate emerging safety information before signing off. This decision reflects how seriously European authorities take monitoring for adverse effects when approving medications that fundamentally alter disease progression, particularly in vulnerable aging populations.

The approval process reveals the tension between making innovative treatments available quickly and ensuring comprehensive safety data in real-world use. The restricted approval applies only to patients with early-stage Alzheimer’s disease who carry no more than one copy of the ApoE4 gene and have confirmed amyloid beta plaques in the brain—a much narrower population than initially hoped. This article explores what prompted the European Commission’s data request, how it affects patients seeking access to lecanemab, what ongoing monitoring requirements now exist, and what the approval signals about future Alzheimer’s treatments in development.

Why Did European Regulators Request Additional Safety Data?
The Genetic Restriction That Limits Access
The Patient Registry Requirement and Ongoing Monitoring
How the Approval Timeline Compares to U.S. and Other European Decisions
The Autoinjector Formulation and Future Access Points
The Role of Biomarker Testing and Patient Selection
What This Approval Signals for Future Alzheimer’s Treatments
Conclusion

Why Did European Regulators Request Additional Safety Data?

The European Commission’s request for additional safety data emerged from a critical gap in the November 2024 EMA recommendation. When the EMA’s Committee for Medicinal Products for Human Use (CHMP) issued its positive opinion, new safety information had already begun surfacing that wasn’t fully integrated into the original dossier. Rather than rubber-stamp approval based on older data, regulators exercised caution—a prudent stance given that lecanemab works through an aggressive mechanism of clearing amyloid plaques from the brain. This approach risks triggering amyloid-related imaging abnormalities (ARIA), a condition where the brain experiences microhemorrhages or microinfarcts, particularly in patients with certain genetic markers.

The timing is important: between November 2024 and April 2025, additional real-world and trial data on lecanemab’s safety profile continued accumulating. European regulators insisted on evaluating this newer information before final approval, demonstrating that their November recommendation was provisional pending further evidence. This is distinct from a clean rejection—the positive opinion remained in place—but it meant the European Commission wasn’t content to simply accept the November assessment without updated analysis. For patients waiting for access, this created a 5-month delay, but it also meant the approved therapy carried fresher safety documentation than would have existed under a faster timeline.

Why Did European Regulators Request Additional Safety Data?

The Genetic Restriction That Limits Access

One of the most significant constraints on lecanemab approval is the restriction to patients with only one copy (heterozygous) or no copies of the ApoE4 gene. The ApoE4 gene is the strongest genetic risk factor for late-onset Alzheimer’s disease, and roughly 25-30% of people carry two copies of this gene. Among those two-copy carriers, lecanemab carries substantially higher risk of amyloid-related imaging abnormalities—the brain inflammation and microhemorrhages that can cause cognitive decline or symptoms mimicking stroke.

However, if you or a family member has access to genetic testing showing you carry zero or one copy of ApoE4, and you have confirmed amyloid plaques on PET imaging or cerebrospinal fluid biomarkers, you’re potentially eligible for the therapy. This genetic gating creates a troubling situation: the people at highest genetic risk for Alzheimer’s disease—ApoE4 homozygotes—are explicitly excluded from the only approved disease-modifying treatment available in Europe. Patients and neurologists have raised concerns that this restriction effectively denies the therapy to those who might benefit most from it, though regulators maintain the exclusion is necessary to avoid unacceptable harm. Anyone considering lecanemab should therefore plan for genetic testing well before discussing treatment options with a neurologist, as this determines eligibility before any other considerations.

The Patient Registry Requirement and Ongoing Monitoring

As a condition of approval, the manufacturers of lecanemab must maintain a comprehensive European patient registry to track every person receiving the drug. This registry serves a critical function: monitoring for rare adverse effects that might not have been visible in clinical trials. Unlike pharmaceutical trials, which typically enroll thousands to tens of thousands of patients for limited durations, real-world use can quickly expose side effects affecting populations trials might have missed—particularly in patients who are older, take multiple medications, or have medical conditions the trials specifically excluded. The registry requirement also reflects a lesson from previous Alzheimer’s medication approvals.

Earlier amyloid-targeting drugs faced safety concerns that weren’t fully appreciated until wider use. By establishing ongoing monitoring for lecanemab from day one, European regulators are essentially building a safety net into the approval itself. Neurologists prescribing lecanemab know they’re participating in a monitored system, and patients should expect regular imaging and biomarker monitoring—not just at initiation, but throughout treatment. This ongoing surveillance requirement will continue generating safety data that may eventually lead to expanded eligibility if the drug proves safer than initial estimates, or further restrictions if unexpected problems emerge.

The Patient Registry Requirement and Ongoing Monitoring

How the Approval Timeline Compares to U.S. and Other European Decisions

The approval of lecanemab in the European Union followed a different pathway than in the United States, where the FDA accelerated approval in January 2023 and granted full approval in July 2023. The U.S. approval faced criticism for moving too quickly and with insufficient diversity in trial populations, whereas the European process involved more cautious scrutiny at multiple decision points. The November 2024 EMA positive opinion, followed by the April 2025 Commission approval with the data request, took nearly two years longer than the U.S. timeline but resulted in what some consider a more evidence-based decision.

This comparison matters for patients abroad who hear about U.S. approvals and wonder why European approval took longer. The extra time allowed for additional safety monitoring and the development of patient registries before approval, not after. Patients in other European nations following the EMA’s recommendation may have earlier access depending on their country’s own regulatory procedures, but the Commission’s April 2025 approval set the standard for the EU member states. For someone living outside the EU seeking treatment, this timeline highlights how regulatory rigor differs between regions—sometimes delaying access, but potentially improving safety profiles in the long run.

The Autoinjector Formulation and Future Access Points

Looking ahead to 2026 and beyond, Eisai submitted supplemental applications for a subcutaneous autoinjector formulation of lecanemab with a once-weekly dosing regimen. Currently approved lecanemab requires intravenous infusion every two weeks, which means patients must travel to a treatment center for each dose. A once-weekly autoinjector would represent a significant quality-of-life improvement, allowing self-administration at home—a major advantage for patients with mobility limitations, transportation challenges, or those living far from infusion centers.

However, switching to an autoinjector formulation isn’t simply a matter of convenience; it involves new safety and efficacy data. Regulators must confirm that subcutaneous administration achieves equivalent drug exposure and tolerability compared to intravenous dosing. If approved, the autoinjector would likely expand access substantially, particularly in rural areas and developing healthcare systems with limited infusion infrastructure. But approval isn’t guaranteed, and the path to subcutaneous formulations for monoclonal antibodies has historically taken 18-36 months after submission—meaning widespread autoinjector availability may not arrive until 2027 or later.

The Autoinjector Formulation and Future Access Points

The Role of Biomarker Testing and Patient Selection

The requirement for “confirmed amyloid beta plaques in the brain” represents another eligibility hurdle that warrants explanation. Patients can’t simply report symptoms and receive lecanemab; they must have objective evidence of amyloid pathology through either positron emission tomography (PET) imaging with amyloid tracers or cerebrospinal fluid biomarker testing (lumbar puncture). This requirement exists because lecanemab’s benefit appears confined to people with amyloid pathology—it doesn’t help patients whose cognitive decline stems from other causes like tau tangles, vascular disease, or Lewy bodies.

For patients and neurologists, this means the approval’s promise is coupled with a diagnostic requirement that not all healthcare systems have readily available. PET imaging for amyloid can cost $3,000-$5,000 and isn’t universally covered by insurance. Lumbar puncture, while cheaper, carries procedural risks and requires specialized labs for biomarker analysis. These access barriers mean that even as lecanemab becomes available, the infrastructure required to identify eligible patients remains a significant constraint in many regions.

What This Approval Signals for Future Alzheimer’s Treatments

The European Commission’s cautious approach to lecanemab approval—requesting additional safety data before final authorization—sets a precedent for how future disease-modifying Alzheimer’s therapies will be scrutinized. Other anti-amyloid monoclonal antibodies in development (such as donanemab, which has shown stronger cognitive benefit than lecanemab in trials) will likely face similar scrutiny around safety data and long-term monitoring requirements. The message from European regulators is clear: approvals of early-stage Alzheimer’s treatments will not be quick, and safety monitoring infrastructure must exist before launch, not after.

This cautious stance also reflects a maturation in how the field understands Alzheimer’s biology. Rather than pursuing the “amyloid cascade hypothesis” with blinders on, regulators now appreciate that clearing amyloid is necessary but not sufficient—and that the process of clearing it can cause harm if applied to the wrong patients or in the wrong way. Future approvals will likely involve even more refined patient selection, genetic testing, imaging requirements, and registries. For someone with Alzheimer’s or a family history of cognitive decline, this means the treatments coming down the pipeline will be more precisely targeted but also more burdensome to access—requiring comprehensive biomarker evaluation before eligibility determination.

Conclusion

The European Commission’s April 2025 approval of lecanemab, contingent on additional safety data evaluation, represents a measured success for Alzheimer’s disease treatment—the first disease-modifying therapy to reach European patients, but with significant restrictions. The approval applies only to people with early-stage cognitive impairment who carry no more than one ApoE4 gene copy and have confirmed amyloid pathology. While this narrows the potential patient population from initial hopes, it reflects regulators’ commitment to preventing harm in vulnerable aging populations.

Patients and families should understand that gaining access requires not only diagnosis, but genetic testing and advanced biomarker imaging to confirm amyloid pathology. Looking forward, the supplemental applications for once-weekly subcutaneous dosing under development by Eisai may expand access significantly if approved. The ongoing European patient registry will provide real-world safety data that could eventually support wider access or lead to further refinements in patient selection. For anyone considering lecanemab or awaiting the next generation of Alzheimer’s treatments, the European regulatory process demonstrates that slower approval timelines often reflect genuine scientific caution rather than obstruction—and that safety monitoring from day one protects patients far more effectively than rapid approval followed by risk discovery.