Lecanemab side effects: what 3,522 FDA adverse event reports show
Drug class
Amyloid Beta-directed Antibody
Brand names
Lecanemab Autoinjector, Leqembi
Who reports
3,522 reports · 43% serious · 154 with death outcome · 59% female
Used for
LEQEMBI is indicated for the treatment of Alzheimer’s disease. Treatment with LEQEMBI should be initiated in patients with mild cognitive impairment or mild dementia stage of disease, the population in which treatment was initiated in clinical trials. LEQEMBI is an amyloid beta-directed antibody indicated for the treatment of Alzheimer’s disease.
What it is
Lecanemab-irmb is a recombinant humanized immunoglobulin gamma 1 (IgG1) monoclonal antibody directed against aggregated soluble and insoluble forms of amyloid beta, and is expressed in a Chinese hamster ovary cell line. Lecanemab-irmb has an approximate molecular weight of 150 kDa.
Boxed warning
AMYLOID RELATED IMAGING ABNORMALITIES Monoclonal antibodies directed against aggregated forms of beta amyloid, including LEQEMBI, can cause amyloid related imaging abnormalities (ARIA), characterized as ARIA with edema (ARIA-E) and ARIA with hemosiderin deposition (ARIA-H). Incidence and timing of ARIA vary among treatments.
Causality screen of the 25 strongest signals
What the badges mean
- Labeled — boxed warning The term (or its clinical synonym) appears in the FDA boxed warning: causality is regulator-recognised and considered serious.
- Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
- Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
- Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
- Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.
Strongest disproportionality signals
Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 9 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Infusion related reaction (reaction during infusion) | 308 | 27.5 24.7–30.6ROR 30.0 · χ² 7,816 / p <1e-300 | 27.3 EB05 24.8 · IC025 +4.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 27.6 · 92% clinician | no trial data cached |
| Cerebral haemorrhage | 121 | 19.9 16.7–23.7ROR 20.6 · χ² 2,150 / p <1e-300 | 19.8 EB05 17.0 · IC025 +3.9 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 22.2 | no trial data cached |
| Cerebral infarction | 78 | 18.8 15.1–23.4ROR 19.2 · χ² 1,291 / p 5e-283 | 18.6 EB05 15.4 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious PRR 25.5 · 96% clinician | no trial data cached |
| Brain oedema | 30 | 14.0 9.8–19.9ROR 14.1 · χ² 348 / p 7e-78 | 13.6 EB05 9.7 · IC025 +2.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 11.5 | no trial data cached |
| Chills | 241 | 12.1 10.7–13.6ROR 12.9 · χ² 2,442 / p <1e-300 | 12.0 EB05 10.8 · IC025 +3.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.3 | no trial data cached |
| Subdural haematoma | 28 | 11.4 7.9–16.6ROR 11.5 · χ² 256 / p 5e-58 | 10.8 EB05 7.6 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 12.8 · 100% clinician | no trial data cached |
| Feeling cold | 42 | 8.8 6.5–11.9ROR 8.9 · χ² 284 / p 5e-64 | 8.3 EB05 6.3 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Brain fog | 19 | 7.6 4.9–12.0ROR 7.7 · χ² 103 / p 2e-24 | 6.7 EB05 4.4 · IC025 +1.9 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.2 | no trial data cached |
| Subarachnoid haemorrhage | 11 | 6.3 3.5–11.4ROR 6.3 · χ² 44 / p 2e-11 | 5.1 EB05 3.0 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 6.3 | no trial data cached |
| Status epilepticus | 12 | 6.2 3.5–11.0ROR 6.2 · χ² 47 / p 3e-12 | 5.1 EB05 3.1 · IC025 +1.4 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 8.5 | no trial data cached |
| Confusional state (confusion) | 170 | 6.2 5.3–7.1ROR 6.4 · χ² 735 / p 4e-162 | 6.1 EB05 5.3 · IC025 +2.3 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.4 | no trial data cached |
| Influenza like illness (flu-like illness) | 74 | 5.3 4.2–6.6ROR 5.3 · χ² 251 / p 6e-57 | 5.1 EB05 4.2 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 1.3 | no trial data cached |
| Ischaemic stroke | 15 | 4.9 3.0–8.2ROR 4.9 · χ² 43 / p 3e-11 | 4.3 EB05 2.8 · IC025 +1.3 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 6.7 | no trial data cached |
| Head discomfort | 14 | 4.7 2.8–7.9ROR 4.7 · χ² 37 / p 7e-10 | 4.1 EB05 2.6 · IC025 +1.1 3/3 methods agree | Not in label — unassessed | serious PRR 1.6 | no trial data cached |
| Headache | 477 | 4.5 4.1–4.9ROR 5.0 · χ² 1,320 / p 3e-289 | 4.4 EB05 4.1 · IC025 +2.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.2 | no trial data cached |
| Aphasia (loss of speech) | 23 | 4.5 3.0–6.7ROR 4.5 · χ² 58 / p 1e-14 | 4.1 EB05 2.9 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 2.8 | no trial data cached |
| Disorientation | 30 | 4.4 3.1–6.3ROR 4.5 · χ² 76 / p 1e-18 | 4.2 EB05 3.1 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 2.7 | no trial data cached |
| Cognitive disorder | 34 | 4.3 3.1–6.0ROR 4.3 · χ² 83 / p 5e-20 | 4.1 EB05 3.1 · IC025 +1.5 3/3 methods agree | Likely indication confounding term in indications | serious PRR 3.1 | no trial data cached |
| Tremor (shaking) | 89 | 3.1 2.6–3.9ROR 3.2 · χ² 129 / p 4e-30 | 3.1 EB05 2.6 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 1.0 | no trial data cached |
| Fracture | 10 | 3.1 1.7–5.8ROR 3.1 · χ² 12 / p 2e-4 | 2.8 EB05 1.7 · IC025 +0.4 | Not in label — unassessed | serious PRR 4.6 | no trial data cached |
| Lethargy | 29 | 3.0 2.1–4.3ROR 3.0 · χ² 36 / p 1e-9 | 2.9 EB05 2.1 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 1.9 | no trial data cached |
| Seizure | 55 | 2.8 2.2–3.7ROR 2.8 · χ² 63 / p 1e-15 | 2.8 EB05 2.2 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.0 | no trial data cached |
| Hypersomnia | 13 | 2.7 1.5–4.6ROR 2.7 · χ² 12 / p 3e-4 | 2.5 EB05 1.6 · IC025 +0.4 | Not in label — unassessed | serious PRR 1.0 | no trial data cached |
| Hallucination (hallucinations) | 30 | 2.3 1.6–3.4ROR 2.4 · χ² 22 / p 1e-6 | 2.3 EB05 1.7 · IC025 +0.6 | Not in label — unassessed | serious PRR 1.1 | no trial data cached |
| Pancreatic carcinoma | 10 | 2.0 1.1–3.7ROR 2.0 · χ² 4 / p 0.021 | 1.9 EB05 1.1 · IC025 -0.1 PRR-only: not supported by EBGM or IC | Not in label — unassessed | serious PRR 2.8 | no trial data cached |
Trial evidence (ClinicalTrials.gov)
Most frequently reported reactions
By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Headache | 477 | 4.5 4.1–4.9ROR 5.0 · χ² 1,320 / p 3e-289 | 4.4 EB05 4.1 · IC025 +2.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 2.2 | no trial data cached |
| Infusion related reaction (reaction during infusion) | 308 | 27.5 24.7–30.6ROR 30.0 · χ² 7,816 / p <1e-300 | 27.3 EB05 24.8 · IC025 +4.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 27.6 · 92% clinician | no trial data cached |
| Chills | 241 | 12.1 10.7–13.6ROR 12.9 · χ² 2,442 / p <1e-300 | 12.0 EB05 10.8 · IC025 +3.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.3 | no trial data cached |
| Confusional state (confusion) | 170 | 6.2 5.3–7.1ROR 6.4 · χ² 735 / p 4e-162 | 6.1 EB05 5.3 · IC025 +2.3 3/3 methods agree | Labeled (related wording) related wording | serious PRR 3.4 | no trial data cached |
| Cerebral haemorrhage | 121 | 19.9 16.7–23.7ROR 20.6 · χ² 2,150 / p <1e-300 | 19.8 EB05 17.0 · IC025 +3.9 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 22.2 | no trial data cached |
| Tremor (shaking) | 89 | 3.1 2.6–3.9ROR 3.2 · χ² 129 / p 4e-30 | 3.1 EB05 2.6 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 1.0 | no trial data cached |
| Cerebral infarction | 78 | 18.8 15.1–23.4ROR 19.2 · χ² 1,291 / p 5e-283 | 18.6 EB05 15.4 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious PRR 25.5 · 96% clinician | no trial data cached |
| Influenza like illness (flu-like illness) | 74 | 5.3 4.2–6.6ROR 5.3 · χ² 251 / p 6e-57 | 5.1 EB05 4.2 · IC025 +2.0 3/3 methods agree | Not in label — unassessed | serious PRR 1.3 | no trial data cached |
| Seizure | 55 | 2.8 2.2–3.7ROR 2.8 · χ² 63 / p 1e-15 | 2.8 EB05 2.2 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.0 | no trial data cached |
| Feeling cold | 42 | 8.8 6.5–11.9ROR 8.9 · χ² 284 / p 5e-64 | 8.3 EB05 6.3 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Cognitive disorder | 34 | 4.3 3.1–6.0ROR 4.3 · χ² 83 / p 5e-20 | 4.1 EB05 3.1 · IC025 +1.5 3/3 methods agree | Likely indication confounding term in indications | serious PRR 3.1 | no trial data cached |
| Hallucination (hallucinations) | 30 | 2.3 1.6–3.4ROR 2.4 · χ² 22 / p 1e-6 | 2.3 EB05 1.7 · IC025 +0.6 | Not in label — unassessed | serious PRR 1.1 | no trial data cached |
| Disorientation | 30 | 4.4 3.1–6.3ROR 4.5 · χ² 76 / p 1e-18 | 4.2 EB05 3.1 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 2.7 | no trial data cached |
| Brain oedema | 30 | 14.0 9.8–19.9ROR 14.1 · χ² 348 / p 7e-78 | 13.6 EB05 9.7 · IC025 +2.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 11.5 | no trial data cached |
| Lethargy | 29 | 3.0 2.1–4.3ROR 3.0 · χ² 36 / p 1e-9 | 2.9 EB05 2.1 · IC025 +0.9 3/3 methods agree | Not in label — unassessed | serious PRR 1.9 | no trial data cached |
Unlabeled candidate signals
These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.
- Cerebral infarction — n=78, PRR 18.8
- Subdural haematoma — n=28, PRR 11.4
- Feeling cold — n=42, PRR 8.8
- Influenza like illness — n=74, PRR 5.3
- Aphasia — n=23, PRR 4.5
- Disorientation — n=30, PRR 4.4
- Tremor — n=89, PRR 3.1
- Lethargy — n=29, PRR 3.0
- Hallucination — n=30, PRR 2.3
Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.
Common questions
What are the most reported side effects of Lecanemab?
In FDA FAERS, the most frequently co-reported reaction terms for Lecanemab are headache, infusion related reaction, chills, confusional state, cerebral haemorrhage, tremor. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.
Does Lecanemab have an FDA boxed warning?
Yes. The current FDA label carries a boxed warning: AMYLOID RELATED IMAGING ABNORMALITIES Monoclonal antibodies directed against aggregated forms of beta amyloid, including LEQEMBI, can cause amyloid related imaging abnormalities (ARIA), characterized as ARIA with edema (ARIA-E) and ARIA with hemosiderin deposition (ARIA-H). Incidence and timing of ARIA vary among treatments.
Do FAERS signals prove that Lecanemab causes these side effects?
No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.
Sources & methods
- FDA label via openFDA (set ID 9d1ff786-e577-410a-a273-c4d7d0e4e975, effective 20260721; matched on
openfda.generic_name.exact:"LECANEMAB") - Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
- FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA
count=aggregation, fieldpatient.drug.openfda.generic_name.exact, 34 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction - Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
- Seriousness and sex counts from openFDA
count=serious,patient.patientsex,seriousnessdeath
Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.