This page shows what was measured, who it was measured in, and what that does not settle.
What Lecanemab does in the body
Used for early Alzheimer disease confirmed by a brain scan or spinal-fluid test.
Alzheimer disease brains accumulate sticky clumps of a protein called amyloid. Lecanemab is an antibody built to grip the clumps, especially the small soluble ones, and flag them for immune cells in the brain to clear away. The plaque does measurably disappear on scans. The clinical effect is a slowing of decline, not a reversal, and the size of that slowing is what the argument is about.
What happened in people
Over 18 months, decline was 1.21 points with lecanemab and 1.66 with a dummy treatment on an 18-point scale.
✓ Reviewed first-read answer
Where this came from
A person wrote this and a reviewer approved it against this exact record. It carries no effect size.
A reviewer approved this against this record. The reviewed-claim record carrying the exact population and effect size does not exist yet.
No source is stored against this line.
The limit that matters most
It is uncertain whether the 0.45-point difference is noticeable to families.
Where it acts
Brain parenchyma and cerebral vasculature
Kind of result
The kind of result is not recorded
Supervision
Professional supervision is normally required. It is a prescription or clinician-administered medicine where it is approved.
What the registries record it as
The substance registry classes this as protein.
FDA substance registry · 12PYH0FTU9 · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
The limit a reviewer approved as the one that matters most here.
The four opening statements run to 103 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Absolute difference
An absolute difference is how many more people in a hundred were affected.
A picture of it, and where the picture fails
It is like counting heads in two rooms of a hundred.
Where that stops being true. Heads are easy to count. Study results carry a margin of error too.
What people get wrong. It is confused with a percentage change, which can look far larger.
The arithmetic difference in event rates between arms.
Confidence interval
A confidence interval is the range the true answer is likely to sit in.
A picture of it, and where the picture fails
It is like a weather forecast giving a range rather than one number.
Where that stops being true. A forecast range covers tomorrow. This one covers what the study could resolve.
What people get wrong. The middle number is read as the answer. A range crossing zero means no change is still possible.
An interval estimate that would contain the true parameter in a stated proportion of repeated studies.
What happened in people◇Read from sources, not yet reviewed
What was measured, goal by goal
One row for each goal a registered study measured something for. One column for each kind of thing that could be measured.
Registered studies list 4 outcome measures that RNAWiki could read. A registered study says what someone planned to measure. It does not say what they found. 0 of the matched studies tested this substance, and 0 posted a result.
There is no single score. A strong test result and a weak life result are different facts.
Goals down the side, kinds of measurement across the top. Each cell says what kind of thing was registered, not what was found.
Goal
Life outcome
What a body can do
How a person feels
A test result
A step in the body
Harms
How long
Who was studied
Focus
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
∅Nothing in the sources checkedNo registered study lists a test result for this goal.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Which registered measures put each goal on this table
Focus
montreal cognitive assessment
Sorted by fixed word lists, version v1. A name the rules do not recognise stays unsorted rather than moving to the nearest column.
What each mark on this table means
∅ Nothing in the sources checked
No registered study lists a life outcome for this goal.
— Not recorded
Harms were not a registered measure for this goal.
… Waiting for a reviewer
Who was studied is listed further down the page.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Change from baseline in CDR-SB at 18 months
✓ The study showed what it set out to show
Who was studied
Clarity AD (NCT03887455)
How many people
1795
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Difference -0.45 (95% CI -0.67 to -0.23), P < 0.001
Repeated elsewhere
Unreplicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Deaths from intracerebral haemorrhage occurred in the open-label extension, several in patients receiving anticoagulation or thrombolysis, which is now addressed in the boxed warning.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Intravenous infusion over one hour every two weeks, with a weekly subcutaneous maintenance autoinjector
Interval reported. 95% CI -0
Written into the record, not signed off as a reviewed claim.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
RNAWiki holds 1 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What happened in people◇Read from sources, not yet reviewed
How close this is to real life
The top step is something a person would feel or care about. The bottom is a guess from software. Filled steps are where evidence exists for this substance.
□Living longer, or avoiding a major eventNo evidence recorded. Death, a heart attack, a stroke, a hospital stay.No registered study measures this.
□What a body can do day to dayNo evidence recorded. Walking, dressing, breathing, recovering.No registered study measures this.
□Measured performanceNo evidence recorded. How much was lifted, how far was run, how fast.No registered study measures this.
□Symptoms and quality of lifeNo evidence recorded. Pain, tiredness, mood, sleep, as the person rated it.No registered study measures this.
□A number that stands in for healthNo evidence recorded. Cholesterol, blood sugar, bone density. A stand-in, not the thing itself.No registered study measures this.
■A step measured inside a personEvidence recorded. Something measured in human tissue or human cells.A human record sits on the stored organism ladder.
□AnimalsNo evidence recorded. Mice, rats, dogs. Useful for ideas, not proof about people.No animal record is stored.
□Cells in a dishNo evidence recorded. Cells or chemistry on a bench, far from a whole body.No cell or bench record is stored.
□A guess from softwareNo evidence recorded. Nobody measured it. RNAWiki never publishes one as a finding.RNAWiki stores no prediction for this record. Software can suggest a link. RNAWiki does not publish one as a finding.
Higher on these steps means closer to something a person would feel. It does not mean better done.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Lecanemab
What a person takes: Intravenous infusion over one hour every two weeks, with a weekly subcutaneous maintenance autoinjector.
The measurement behind this step
10 mg/kg every two weeks intravenously. A 360 mg weekly subcutaneous autoinjector was approved in 2025 for maintenance, based on matched pharmacokinetics and amyloid reduction rather than a separate clinical outcome trial.
Getting in
Intravenous infusion every two weeks
An hour-long drip every fortnight, at a dose set by body weight. A weekly under-the-skin injection was approved later for maintenance.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
10 mg/kg every two weeks by one-hour infusion, with a subcutaneous 360 mg weekly maintenance option approved in 2025 on the basis of matched pharmacokinetic exposure and amyloid reduction rather than a separate outcome trial.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
Reaching the cell
Crossing into the brain, inefficiently
Only a very small proportion of any antibody gets past the blood-brain barrier. That is why the dose is so large and the infusions so frequent.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Central nervous system penetration of an intact IgG is on the order of 0.1-0.3% of plasma concentration, achieved largely by transcytosis and bulk flow. This constraint, not target biology, sets the dosing regimen for every anti-amyloid antibody.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
What it acts on
Binding soluble protofibrils preferentially
It grips the small soluble clumps of amyloid rather than only the large hardened plaques, which is the design choice that distinguishes it from earlier antibodies.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Derived from mAb158, raised against the Arctic APP mutation protofibril. Affinity is roughly an order of magnitude higher for soluble protofibrils than for insoluble fibrils and far higher than for monomer, a selectivity profile that motivated the protofibril toxicity hypothesis this drug was built to test.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
The change it makes
Microglia clear the opsonised aggregates
The antibody tags the clumps and the brain resident immune cells eat them. The same process, acting on amyloid in vessel walls, is what causes the swelling and bleeding.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
FcgammaR-mediated microglial phagocytosis removes opsonised aggregates. Where amyloid is deposited in the vessel wall as cerebral amyloid angiopathy, the same clearance transiently weakens vascular integrity, producing the fluid leakage of ARIA-E and the microbleeds of ARIA-H. ARIA is therefore a direct consequence of the mechanism working, not an off-target effect.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
What that does for a person
Plaque falls below the positivity threshold; decline slows by a small amount
Amyloid scans become negative in most treated patients. Cognitive and functional decline continues, at a measurably but modestly slower rate.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Amyloid PET change of -72.5 centiloids in the phase 2 substudy takes most patients below the 24-30 centiloid positivity threshold. CDR-SB decline is slowed by 0.45 points over 18 months. The gap between near-complete target removal and a 27% clinical effect is the central unresolved observation about the amyloid hypothesis.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
People with mild cognitive impairment or mild dementia due to Alzheimer disease, with amyloid confirmed by PET or cerebrospinal fluid, who can attend for infusions and repeated MRI monitoring.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
Where the result stopped carrying
Every earlier anti-amyloid antibody that targeted plaque or monomer rather than protofibrils failed to show clinical benefit, including bapineuzumab and solanezumab
The ApoE e4 homozygous subgroup, at highest genetic risk, showed no primary-endpoint effect and the highest ARIA rates
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied for a different goal
The studies measured something else entirely.
On this record: Some registered studies measured things that match no goal on this page.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (10)
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Given by a clinician
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Intravenous infusion over one hour every two weeks, with a weekly subcutaneous maintenance autoinjector
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
Professional supervision is normally required. It is a prescription or clinician-administered medicine where it is approved.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
The identity record classes it as Monoclonal Antibody (mAb).
No source is stored against this line.
What is in the pack
10 mg/kg every two weeks intravenously. A 360 mg weekly subcutaneous autoinjector was approved in 2025 for maintenance, based on matched pharmacokinetics and amyloid reduction rather than a separate clinical outcome trial.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
Boxed warning for amyloid related imaging abnormalities, which can be fatal, and for higher incidence in ApoE e4 homozygotes. MRI is required at baseline and before the fifth, seventh and fourteenth infusions. Infusion-related reactions occur in about a quarter of patients on first exposure.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
ClinicalTrials.gov, Clarity AD (NCT03887455) · a recorded source, not a stored snapshot
Drugs@FDA, LEQEMBI BLA 761269, accelerated approval 6 January 2023 and traditional approval 6 July 2023 (https://www.accessdata.fda.gov/scripts/cder/daf/inde… · a recorded source, not a stored snapshot
Reports sent to a regulator
These are reports people sent to a regulator. They do not show the medicine caused the reaction.
Nobody counted how many people took the medicine and reported nothing.
The same event can be reported more than once, and many reports are incomplete.
News coverage, lawsuits and new warnings change how often people report.
A count is not a rate and not a risk.
Lecanemab appears in spontaneous reports to regulators. Across the 6 most-reported reaction terms, 38 reaction mentions were counted. One report can name several reactions.
The recorded terms (6)
amyloid related imaging abnormality-oedema/effusion — 15 reaction mentions
amyloid related imaging abnormality-microhaemorrhages and haemosiderin deposits — 14 reaction mentions
cerebral microhaemorrhage — 4 reaction mentions
brain fog — 2 reaction mentions
superficial siderosis of central nervous system — 2 reaction mentions
cerebral sulcal prominence — 1 reaction mentions
open-targets-adr · recorded 2026-06-24 · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Intravenous infusion over one hour every two weeks, with a weekly subcutaneous maintenance autoinjector
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
A 360 mg weekly subcutaneous autoinjector was approved in 2025 for maintenance, based on matched pharmacokinetics and amyloid reduction rather than a separate clinical outcome trial.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
6 products list this as an active ingredient in the United States drug directory. 6 of them contain it and nothing else.
FDA National Drug Code directory · 62856-212 · read 2026-08-29
They are sold as injection, solution and liquid, taken intravenous.
FDA National Drug Code directory · 62856-212 · read 2026-08-29
The regulator's established pharmacologic class for it is amyloid beta-directed antibody interactions [moa] and amyloid beta-directed antibody [epc].
FDA National Drug Code directory · 62856-212 · read 2026-08-29
1 published label names it as an active ingredient. None of them describes this substance alone, so no label text on this page can be attributed to it rather than to a combination.
US prescribing information · 9d1ff786-e577-410a-a273-c4d7d0e4e975 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 9d1ff786-e577-410a-a273-c4d7d0e4e975 · read 2026-08-29
LEQEMBI is intravenous at 3 DOSAGE FORMS AND STRENGTHS Lecanemab-irmb is a clear to very opalescent, colorless to pale yellow solution, available as: Intravenous Infusion Injection: 500 mg/5 mL (100 mg/mL) in a single-dose vial Injection: 200 mg…, recorded as fda label in effect 2026-07-21 in the United States.
US prescribing information · 9d1ff786-e577-410a-a273-c4d7d0e4e975 · read 2026-08-30
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
Self-experiment planning is not offered for a prescription or clinician-supervised medicine. The questions below are for a clinician or pharmacist.
Questions worth asking
Which of the trials of Lecanemab studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That a 0.45-point CDR-SB difference is a change patients or families would perceive; published estimates of the minimal important difference are larger
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That an 18-month slowing implies continued divergence over years; the trial cannot distinguish disease modification from a fixed offset
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That removing amyloid is now proven to be the mechanism of benefit; the effect size is far smaller than near-complete target removal would predict
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
How fast does the body clear it?
The sources RNAWiki checked hold nothing for this field.
Why it matters. Without this, nothing on this page can say how long anything lasts.
What would answer it
A stored source that records it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
Clarity AD: CDR-SB decline of 1.21 against 1.66, a difference of 0.45 points on an 18-point scale
In plain words
Over 18 months, people on lecanemab got worse by 1.21 points on an 18-point disability scale and people on placebo got worse by 1.66. The difference of 0.45 points, or 27% less decline, is the entire clinical result.
What was measured
CDR-SB difference -0.45 (95% CI -0.67 to -0.23), P < 0.001, 27% slowing
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Randomised, double-blind, placebo-controlled 18-month phase 3 trial. 1,795 participants randomised, 898 to lecanemab 10 mg/kg every two weeks and 897 to placebo. Mean baseline CDR-SB was approximately 3.2 in both groups. Adjusted least-squares mean change at 18 months was 1.21 with lecanemab and 1.66 with placebo; difference -0.45 (95% CI -0.67 to -0.23), P < 0.001. ADAS-Cog14 difference -1.44 and ADCS MCI-ADL difference 2.0 both favoured lecanemab.
Written into the record, not signed off as a reviewed claim
Amyloid was removed, and that part is not in dispute
In plain words
Brain scans showed the amyloid plaque burden falling to below the threshold used to define a positive scan in most treated patients. The drug does what it was designed to do at the level of the target.
What was measured
Amyloid PET change -72.5 centiloids versus 1.0 on placebo at week 79
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
In the phase 2 amyloid PET substudy, adjusted mean change from baseline at week 79 was -72.5 centiloids on lecanemab against 1.0 on placebo, from mean baselines of 78.0 and 84.8 centiloids, a difference of -73.5 (P < 0.001). Clarity AD reproduced substantial amyloid reduction. Target engagement and plaque removal are the best-established facts about this drug.
Source
LEQEMBI US Prescribing Information, Clinical Studies, amyloid PET substudy
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
A 0.45-point difference is presented as a clinically meaningful slowing of Alzheimer disease
In plain words
Whether 0.45 points on an 18-point scale is something a family would notice has never been established. Published estimates of the smallest CDR-SB change that matters to patients are generally larger than the effect measured.
What was measured
That a 0.45-point CDR-SB difference over 18 months is a change patients and families would perceive
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The CDR-SB runs from 0 to 18. Published estimates of the minimal clinically important difference in mild cognitive impairment and mild dementia populations generally sit in the range of one to two points, above the 0.45 measured here. The trial was 18 months long, which cannot distinguish a genuine slowing of the disease process from a fixed offset that would not widen with time. Presenting the result as a percentage, 27% less decline, makes it sound larger than the absolute number does, and both descriptions are of the same measurement.
Source
CDR-SB scale properties and the 18-month duration of Clarity AD
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
contested
Review state
Written into the record, not signed off as a reviewed claim
ARIA: brain swelling in 13% and microbleeding in 17%, with fatal intracerebral haemorrhage reported
In plain words
One patient in eight developed brain swelling and one in six developed small brain bleeds. Most were symptomless and found only on the required MRI scans, but serious and fatal events have occurred and the drug carries a boxed warning.
What was measured
ARIA-E 13% versus 2%; ARIA-H 17% versus 9%; intracerebral haemorrhage >1 cm 0.7% versus 0.1%
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
From the label, in Study 2: ARIA of any type in 21% (191/898) on lecanemab versus 9% (84/897) on placebo; ARIA-E in 13% (113/898) versus 2% (15/897); ARIA-H in 17% (152/898) versus 9% (80/897). Symptomatic ARIA in 3% (29/898), serious symptoms in 0.7% (6/898). Intracerebral haemorrhage larger than 1 cm in 0.7% (6/898) versus 0.1% (1/897), with fatal events observed. Monitoring MRIs are required before the fifth, seventh and fourteenth infusions.
Source
LEQEMBI US Prescribing Information, boxed warning and Warnings and Precautions 5.1
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
In ApoE e4 homozygotes no effect on the primary endpoint was observed, and their ARIA risk is the highest
In plain words
The 15% of patients carrying two copies of the highest-risk Alzheimer gene had the worst safety profile and, in an exploratory analysis, showed no benefit on the main outcome measure at all.
What was measured
No CDR-SB treatment effect observed in ApoE e4 homozygotes; ARIA in 45% versus 22% on placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The label states that in an exploratory subgroup analysis of ApoE e4 homozygotes, representing 15% of the trial population, a treatment effect was not observed on the primary CDR-SB endpoint, although secondary clinical endpoints and biomarkers favoured lecanemab. In the same subgroup, ARIA occurred in 45% on lecanemab versus 22% on placebo, and symptomatic ARIA-E in 9% against 2% of heterozygotes and 1% of noncarriers. ApoE genotyping before treatment is recommended in the boxed warning for exactly this reason. This is the group with the strongest genetic case for treating and the weakest measured benefit-to-risk ratio.
Source
LEQEMBI US Prescribing Information, Clinical Studies and Warnings and Precautions 5.1
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
From accelerated approval on a surrogate to traditional approval on an outcome, in six months
In plain words
Lecanemab was first approved in January 2023 on amyloid removal alone, the same basis as aducanumab. When the outcome trial read out, it converted to full approval in July 2023. That is the pathway working as designed, and it is why this drug is not aducanumab.
What was measured
Not recorded
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Accelerated approval under BLA 761269 was granted on 6 January 2023 on the amyloid surrogate. Traditional approval followed on 6 July 2023 on the strength of Clarity AD. The contrast with aducanumab, whose confirmatory trial was never completed and which was withdrawn from the market, is the clearest available illustration of what accelerated approval is supposed to do and what happens when the confirmation does not arrive.
Source
Drugs@FDA record for LEQEMBI BLA 761269
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
Where else this substance is registered
FDA substance identifier (UNII)
12PYH0FTU9
CAS registry number
1260393-98-3
WHO international nonproprietary name list entry
11194
EMA substance identifier
300000023654
DrugBank
DB14580
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No registered study is classified as testing this substance.
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Safety mode resolved
The identity record classes it as Monoclonal Antibody (mAb).
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What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
What the approval register records
The earliest marketing start date recorded for a listed product is 20221216.
FDA National Drug Code directory · 62856-212 · read 2026-08-29
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The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
An antibody targeting amyloid beta protofibrils that slowed decline on the 18-point CDR-SB by 0.45 points over 18 months in 1,795 patients, while causing brain swelling in 13% and brain microbleeding in 17%.
Recorded evidence blocks (10)
Q1
What did Lecanemab's largest trial (1906 people) and its longest (16 years) measure?
1906 people in Lecanemab's largest registered study, 16 years in its longest registered window, measuring To Determine Whether Anti-Amyloid Mabs Slow Cognitive And Functional Decline. ClinicalTrials.gov · 2026-09-01
6 phase3, 4 phase2, 3 na or unstated, 3 phase1, 1 early phase1, 1 na, 1 phase4; NCT01760005; 2028-07; no ageing endpoint recorded. Last human test completed 2024, NCT01767311.
Interpretation These counts include studies where Lecanemab was a comparison treatment, a background treatment or an exposure in an observational study, and the longest window may be a planned end date. Trial roles have not yet been classified for this record.
Show the evidence
phase3
6
phase2
4
na or unstated
3
phase1
3
early phase1
1
na
1
2 more recorded rows
phase4
1
Last recorded human testNCT01767311
2024-12-10
recorded 2026-09-01 · last checked 2026-09-04
Q2
Lecanemab was tested only in human — what did it show?
3 recorded entries; human; also "Lecanemab 5.0 mg/kg", "Lecanemab 10 mg/kg"
Show the evidence
human
NCT01767311
Lecanemab 2.5 mg/kg
NCT01767311
Lecanemab 5.0 mg/kg
NCT01767311
Lecanemab 10 mg/kg
recorded 2026-09-01 · last checked 2026-09-04
Q4
Could one person measure Lecanemab's effect on treatment intervention related adverse events?
Treatment intervention related adverse events: measured in Lecanemab's trials.
Interpretation treatment intervention related adverse events is the recorded endpoint.
Show the evidence
biomarkers
treatment intervention related adverse events; 2026-09-01
treatment intervention related serious adverse events; 2026-09-01
montreal cognitive assessment; 2026-09-01
feasibility of enrollment; 2026-09-01
human trials at or under30
2
Not recorded for this substance
a recorded half-life
smallest human trial
15; NCT05469009; EARLY_PHASE1; the smallest recorded human enrolment at or below 30; the registry states no direction of its result; ACTIVE_NOT_RECRUITING
Q5
Which of feasibility of enrollment, montreal cognitive assessment and treatment intervention related adverse events did Lecanemab's trials measure?
feasibility of enrollment, montreal cognitive assessment and treatment intervention related adverse events lead 4 outcome terms across Lecanemab's trials. ClinicalTrials.gov · 2026-09-01
Interpretation feasibility of enrollment follow.
Show the evidence
treatment intervention related adverse events
1
treatment intervention related serious adverse events
1
montreal cognitive assessment
1
feasibility of enrollment
1
recorded 2026-09-01 · last checked 2026-09-04
Q6
Which of Lecanemab's 13 ongoing trials reports first?
Assess cognitive efficacy in individuals with mutations causing dominantly inherited AD as measured by the change from baseline in the DIAN-Multivariate Cognitive Endpoint…; Core Study: Change from Baseline in the CDR-SB at 18 Months; latest 2031-01-16
Show the evidence
Trial
NCT01760005
"Dominantly Inherited Alzheimer Network Trial: An Opportunity to Prevent Dementia. A Study of Potential Disease Modifying Treatments in Individuals at Risk for or With a Type of Early Onset Alzheimer's Disease Caused by a Genetic Mutation. Master Protocol DIAN-TU-001"; n 490; "Assess cognitive efficacy in individuals with mutations causing dominantly inherited AD as measured by the change from baseline in the DIAN-Multivariate Cognitive Endpoint (DIAN-MCE)"; 2028-07
NCT03887455
"A Study to Confirm Safety and Efficacy of Lecanemab in Participants With Early Alzheimer's Disease"; n 1906; "Core Study: Change from Baseline in the CDR-SB at 18 Months"; 2029-06-30
NCT04468659
"AHEAD 3-45 Study: A Study to Evaluate Efficacy and Safety of Treatment With Lecanemab in Participants With Preclinical Alzheimer's Disease and Elevated Amyloid and Also in Participants With Early Preclinical Alzheimer's Disease and Intermediate Amyloid"; n 1400; "A45 Trial: Change From Baseline in Preclinical Alzheimer Cognitive Composite 5 (PACC5) Score at Week 216"; 2031-01-16
NCT05269394
"Dominantly Inherited Alzheimer Network Trial: An Opportunity to Prevent Dementia. A Study of Potential Disease Modifying Treatments in Individuals With a Type of Early Onset Alzheimer's Disease Caused by a Genetic Mutation (DIAN-TU)"; n 197; "The primary end point is the change from Week 24 to Week 104 and Week 208 in tau PET in the Symptomatic Population (Cohort 1)."; 2028-07
NCT05469009
"Safety and Feasibility of Exablate Blood-Brain Barrier Disruption for Mild Cognitive Impairment or Mild Alzheimer's Disease Undergoing Standard of Care Monoclonal Antibody (mAb) Therapy"; n 15; "Treatment intervention related adverse events"; 2029-07
NCT05925621
"Cognitive Neurology Unit Clinical Registry"; n 500; "To Determine Whether Anti-Amyloid Mabs Slow Cognitive And Functional Decline"; 2028-06
7 further recorded trials
NCT05999084
"Georgia Memory Net Anti-Amyloid Monoclonal Antibody Registry"; n 735; "Change in Quick Dementia Rating System (QDRS) Score"; 2028-07
NCT06285448
"Feasibility of Lecanemab Registry and Clinical Outcome Measures"; n 20; "Feasibility of enrollment"; 2028-06-30
NCT06384573
"DIAN-TU Amyloid Removal Trial (ART) in Dominantly Inherited Alzheimer's Disease"; n 40; "The primary endpoint for the final analysis is the time to recurrent progression of Clinical Dementia Rating - Sum of Boxes (CDR-SB)."; 2030-06
NCT06530732
"Deep Cervical Lymphatlc-Venous Anastomosis Surgery for the Treatment of Alzheimer's Disease: A Pilot Study (DIVA Study)"; n 60; "The rate of change in the total score of the Clinical Dementia Rating Scale"; 2026-09-30
NCT06602258
"A Study of E2814 With Concurrent Lecanemab Treatment in Participants With Early Alzheimer's Disease"; n 105; "Change From Baseline in CSF MTBR-tau-243 at 6 Months"; 2027-08-18
NCT07544953
"Amyloid Monoclonal Antibody Treatment in PD Patients With Coexistent AD Pathology"; n 60; "Changes in amyloid dposition on amyloid imaging scans"; 2030-11
NCT07688460
"Evaluation System for Lecanemab Efficacy Using Gold Electrode ECL to Monitor Alzheimer's Biomarkers"; n 100; "Change in Plasma Alzheimer's Biomarkers"; 2029-03-30
recorded 2026-09-01 · last checked 2026-09-04
Q7
Which 3 trials of Lecanemab posted no result?
Posted no result
3 of 3 completed trials
Registrations
NCT01230853, NCT05045716 and NCT05533801
Completion dates
oldest 2013-02; newest 2023-01-06
Show the evidence
Trial
NCT01230853
2013-02
NCT05045716
2021-12-07
NCT05533801
2023-01-06
Q8
At the median, Lecanemab's trials enrolled 105 people — anything larger?
Median enrolment
105
Largest enrolment
1906
Registered trials counted
17
Q9
What do 38 spontaneous reports say about Lecanemab — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
Lecanemab appears in spontaneous reports to regulators. Across the 6 most-reported reaction terms, 38 reaction mentions were counted: amyloid related imaging abnormality-oedema/effusion 15; amyloid related imaging abnormality-microhaemorrhages and haemosiderin deposits 14; cerebral microhaemorrhage 4; brain fog 2. open-targets-adr · CHEMBL3833321 · 2026-06-24
Show the evidence
amyloid related imaging abnormality-oedema/effusion
15
amyloid related imaging abnormality-microhaemorrhages and haemosiderin deposits
14
cerebral microhaemorrhage
4
brain fog
2
superficial siderosis of central nervous system
2
cerebral sulcal prominence
1
recorded 2026-06-24 · last checked 2026-09-04
Q10
Was Lecanemab studied with exercise?
exercise is named in Lecanemab's label sentences: "Although melatonin and aerobic exercise for a short time were significantly more effective than donanemab, lecanemab, aducanumab and placebo in the primary analysis, there was significant heterogeneity." openfda-label+europepmc · 2024-01-01
1 recorded statement; exercise
Show the evidence
exercise
Although melatonin and aerobic exercise for a short time were significantly more effective than donanemab, lecanemab, aducanumab and placebo in the primary analysis, there was significant heterogeneity.
recorded 2024-01-01 · last checked 2026-09-04
Where it is registeredIdentifiers, relations and other names
ChEMBL ATC CC BY-SA · ClinicalTrials.gov — US Government work · Europe PMC — metadata only, under the recorded legal gate · Open Targets 26.06 — CC0 · derived from this page's own recorded fields; no external licence · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
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