A quiet but explosive legal crisis is unfolding in 2026 around two blockbuster Alzheimer’s drugs — Leqembi and Kisunla — and the patients and trial volunteers who were never told their DNA put them at deadly risk. The Leqembi Kisunla lawsuit landscape is accelerating fast, driven by documented deaths, a landmark investigative report, an FDA safety mandate, a formal European rejection of Kisunla, and a growing coalition of plaintiffs’ attorneys filing individual cases before any federal multidistrict litigation has been consolidated. If you or a loved one participated in a clinical trial or received either drug commercially and suffered a serious brain injury, this pre-MDL window may be the most important moment to act.
What Are Leqembi and Kisunla — and Why Are They Killing Some Patients?
Leqembi (lecanemab-irmb), manufactured by Eisai and Biogen, received FDA accelerated approval in January 2023 and traditional approval in July 2023 to slow the progression of early Alzheimer’s disease. Kisunla (donanemab), manufactured by Eli Lilly, received FDA approval in July 2024. Both are anti-amyloid monoclonal antibody infusions designed to clear beta-amyloid plaques from the brain — a protein believed to contribute to Alzheimer’s progression. Both drugs share a dangerous and potentially fatal side effect profile centered on a condition called ARIA, or amyloid-related imaging abnormalities.
ARIA takes two forms: ARIA-E (brain swelling and edema) and ARIA-H (microhemorrhage and hemosiderin deposits). According to the FDA’s drug safety communications, fatal events involving intracranial hemorrhage have been observed with Leqembi, and the label explicitly warns that intracerebral hemorrhage greater than 1 cm in diameter was reported in 0.7% of Leqembi patients versus 0.1% with placebo. For patients carrying two copies of the APOE4 gene — a known Alzheimer’s risk factor — the danger is dramatically magnified. Bloomberg’s investigative review found that nearly 33% of two-copy APOE4 carriers on Leqembi experienced brain swelling, compared to just 5% of non-carriers. To understand what financial damages may be available to victims of defective drug brain injuries, use our brain injury calculator as a starting reference point.
The APOE4 Informed-Consent Scandal: What Manufacturers Knew and Withheld
The core of the current Leqembi Kisunla lawsuit wave is not merely that patients were harmed — it is that the drug manufacturers allegedly knew which patients faced catastrophic risk and said nothing. An investigative report revealed that Eisai conducted genetic testing on approximately 2,000 volunteers enrolled in the CLARITY AD clinical trial for Leqembi and identified which participants carried the APOE4 gene. Despite having this information, Eisai did not disclose individual genetic results to the volunteers — leaving approximately 274 high-risk participants uninformed of their dramatically elevated ARIA risk before they continued receiving infusions.
The pattern extends to Kisunla. Eli Lilly likewise failed to inform TRAILBLAZER-ALZ 2 / REMAIN trial volunteers of their APOE4 carrier status despite possessing the data and knowing the gene’s implications for ARIA severity. This is not a passive omission — it is what legal scholars describe as a failure of informed consent, a cornerstone of medical ethics and tort law. Under federal informed consent regulations codified at 21 CFR § 50.25, clinical trial participants must be provided all information that might affect their willingness to participate, including foreseeable risks. Withholding known genetic risk data from enrolled participants arguably violates this standard directly.
Deaths, Disabilities, and the Data That Cannot Be Ignored
The human toll documented in 2026 is stark. Bloomberg’s adverse event investigation documented at least 7 U.S. deaths linked to Leqembi and 3 patients left with lasting disabilities. A real-world case reported at a major neurology conference involved an APOE4 homozygote treated at Columbia University: the patient had only one baseline microhemorrhage, developed severe ARIA-E after the third infusion, suffered uncontrolled seizures, and died. An autopsy study published in Nature Communications (Solopova et al.) of a woman who died while on Leqembi found blood vessels in the meninges packed with amyloid and bulging with multiple aneurysms — peer-reviewed forensic evidence that the drug’s mechanism can cause catastrophic vascular damage in susceptible individuals.
The Kisunla trial data reviewed by the European Medicines Agency tells a parallel story. ARIA occurred in 36.8% of Kisunla recipients versus 14.9% in placebo patients. Serious ARIA events occurred in 1.6% of Kisunla patients. Three deaths in the Kisunla clinical trials were directly attributed to ARIA. Based on analysis of publicly available trial data, approximately 100 clinical trial participants across both drugs suffered documented brain bleeds and swelling. For families who lost a loved one, these are not statistics — they are the foundation of viable Leqembi Kisunla lawsuit claims, and our wrongful death calculator can help families begin to understand the scope of damages in fatal mass tort cases.
Key Safety Statistics at a Glance
| Metric | Leqembi (CLARITY AD) | Kisunla (TRAILBLAZER-ALZ 2) | Source |
|---|---|---|---|
| Overall ARIA rate | ~21% (any ARIA) | 36.8% | FDA labels / EMA assessment |
| ARIA-E in APOE4 homozygotes | ~33% (two-copy carriers) | Elevated (EMA cited) | Bloomberg investigation |
| ARIA-E in non-carriers | ~5% | Not separately published | Bloomberg investigation |
| Serious ARIA events | Documented fatal ICH events | 1.6% serious events | FDA label / EMA report |
| Clinical trial deaths from ARIA | Documented (Bloomberg: 7 U.S. deaths) | 3 confirmed deaths | Bloomberg / EMA |
| Trial participants with undisclosed APOE4 status | ~274 (CLARITY AD) | Unreported (REMAIN trial) | NYT investigation / Bloomberg |
| ICH >1 cm diameter rate | 0.7% vs. 0.1% placebo | Not separately reported | FDA Leqembi label |
Regulatory Actions: FDA Mandates and Europe’s Outright Rejection
Regulatory bodies on both sides of the Atlantic have now taken concrete action that strengthens the legal position of Leqembi Kisunla lawsuit plaintiffs. On August 28, 2025, the FDA issued a formal safety communication ordering additional early MRI monitoring for Leqembi patients — specifically, enhanced imaging before the third infusion to detect ARIA-E before it becomes fatal. This mandate is a direct acknowledgment that the monitoring protocols in place at the time of approval were insufficient to protect patients. The FDA’s FAERS (FDA Adverse Event Reporting System) database continues to accumulate post-market adverse event reports involving deaths and serious disability.
In Europe, the regulatory verdict was even more decisive. The European Medicines Agency formally refused marketing authorization for Kisunla on March 27, 2025, concluding that the drug’s benefits were “not large enough to outweigh the risks of potentially fatal events due to ARIA.” This is not a conditional approval or a labeling update — it is a complete rejection based on a risk-benefit analysis that European regulators found unacceptable. The EU’s conclusion directly contradicts the FDA’s approval rationale and provides powerful cross-jurisdictional evidence that Eli Lilly’s risk disclosures were inadequate. Plaintiffs filing claims can reference the FDA’s own MedWatch adverse event reporting program data as part of building their cases.
Legal Theories, Who Can File, and the Pre-MDL Opportunity
The current Leqembi Kisunla lawsuit litigation rests on three primary legal theories. First, failure to obtain informed consent in clinical trials: manufacturers knew APOE4 genetic results and withheld them from trial participants, depriving those individuals of the information they needed to make an autonomous decision about continuing participation. Second, failure to warn commercial patients: post-approval Leqembi and Kisunla patients were not adequately counseled about APOE4-specific lethal ARIA risk before and during treatment. Third, negligence in study design and monitoring: the clinical trial protocols were structured in ways that foreseeably exposed vulnerable genetic subgroups to unreasonable harm without adequate protective measures or exit criteria.
Firms actively pursuing claims as of mid-2026 include Seeger Weiss (which updated its case page on July 7, 2026), Moll Law Group, Phillips Law, and others documented by Lawsuit Information Center. Crucially, no MDL has been filed or consolidated as of October 2026. Cases remain in early individual filing stages across multiple federal districts. This is the pre-MDL window that legal history consistently shows favors early plaintiffs — those who file early often secure better individual attention to their claims and potentially stronger negotiating positions in any eventual consolidation. Eligible plaintiffs include CLARITY AD and Leqembi clinical trial participants who carry the APOE4 gene and suffered ARIA brain bleeds or swelling without being informed of their genetic risk; TRAILBLAZER-ALZ 2 participants in the same situation; and commercial patients who developed serious ARIA, brain hemorrhage, disability, or death without adequate APOE4 genetic counseling prior to treatment. Our medical malpractice calculator can help injured patients and families begin quantifying damages in defective drug injury cases.
Statutes of limitations vary significantly by state. Under principles established in federal drug litigation, the clock typically begins running when a plaintiff knew or reasonably should have known of the connection between the drug and their injury — but genetic non-disclosure cases present unique accrual questions that courts have not yet uniformly resolved. Information on state-level statutes of limitations is available through Justia’s state statute of limitations database. Waiting risks being time-barred regardless of the strength of the underlying claim.
Frequently Asked Questions About the Leqembi Kisunla Lawsuit
Who qualifies to file a Leqembi or Kisunla lawsuit in 2026?
You may qualify if you or a family member (1) participated in the CLARITY AD clinical trial for Leqembi or the TRAILBLAZER-ALZ 2 trial for Kisunla and carry the APOE4 gene but were never informed of your genetic results or elevated risk; (2) received Leqembi or Kisunla as a commercial patient after FDA approval and developed serious ARIA, brain swelling, intracranial hemorrhage, lasting disability, or died; or (3) are the surviving family member of someone who died from drug-related ARIA complications. APOE4 carrier status is particularly central to the strongest claims, but commercial patients who suffered serious harm without adequate genetic counseling may also have valid cases.
What is ARIA and why is it so dangerous for APOE4 carriers?
ARIA stands for amyloid-related imaging abnormalities and encompasses two distinct injury patterns: ARIA-E (brain edema and swelling) and ARIA-H (microhemorrhages and hemosiderin deposits). ARIA occurs when the drug’s anti-amyloid mechanism disrupts blood vessel integrity in the brain. For patients who carry two copies of the APOE4 gene (homozygotes), Bloomberg’s investigation found that approximately 33% experienced brain swelling compared to just 5% of non-carriers — a more than sixfold increased risk. In severe cases, ARIA progresses to uncontrolled seizures, massive intracranial hemorrhage, and death, as documented in real-world cases reported at major neurology conferences and in peer-reviewed autopsy studies published in 2026.
What legal claims form the basis of the Leqembi Kisunla lawsuit?
The primary legal theories include: (1) failure to obtain informed consent — both Eisai and Eli Lilly allegedly conducted genetic testing that identified APOE4 carriers among trial volunteers but withheld those results, violating federal informed consent regulations under 21 CFR § 50.25; (2) failure to warn commercial patients about APOE4-specific lethal ARIA risk before and during treatment; and (3) negligence in clinical trial design and safety monitoring, including inadequate protocols for the highest-risk genetic subgroups. The FDA’s August 2025 safety mandate and the EMA’s complete rejection of Kisunla in March 2025 both serve as supporting evidence that manufacturer disclosures were insufficient.
Is there a Leqembi or Kisunla MDL class action yet?
As of October 2026, no multidistrict litigation (MDL) has been filed or consolidated for Leqembi or Kisunla cases. Litigation remains in the individual case filing stage, with multiple plaintiffs’ firms — including Seeger Weiss, which updated its active case page in July 2026 — pursuing claims on behalf of individual plaintiffs in various federal districts. This pre-MDL phase is historically significant: plaintiffs who file during this window often benefit from more individualized case development, potentially stronger positions in any future consolidation, and earlier access to the discovery process. Waiting for an MDL to form before taking action is not advisable given applicable statutes of limitations.
What damages can Leqembi or Kisunla victims potentially recover?
While no settlement values or jury verdicts have been published in the Leqembi Kisunla lawsuit litigation as of 2026 — making any specific figures entirely speculative — typical categories of damages in pharmaceutical injury mass tort cases include past and future medical expenses, rehabilitation and long-term care costs, lost wages and earning capacity, pain and suffering, loss of consortium for family members, and punitive damages if willful concealment of genetic risk data is proven. In fatal cases, wrongful death damages may also include funeral expenses and loss of financial support. Because this litigation is in early stages, consultation with a qualified plaintiffs’ attorney is essential to assess the specific value of any individual claim.
Legal Disclaimer: The information provided on this page is for general informational purposes only and does not constitute legal advice, create an attorney-client relationship, or substitute for consultation with a licensed attorney qualified in pharmaceutical mass tort litigation in your jurisdiction.
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Victoria Chambers is a mass tort and class action research analyst with extensive knowledge of multi-district litigation (MDL), defective product cases, dangerous drug lawsuits, and toxic exposure claims across the United States. Victoria is not an attorney and the information provided is for educational purposes only.