This page shows what was measured, who it was measured in, and what that does not settle.
What Levocetirizine does in the body
Hay fever, year-round nasal allergy, and long-running hives
When you meet something you are allergic to, cells in your nose and skin dump histamine, and histamine is the chemical that makes you itch, sneeze and run. Histamine works by switching on a receptor that sits on blood vessels and on nerve endings. Levocetirizine parks itself in that receptor and holds it in the off position, so the histamine that gets released has nowhere to act. It does nothing about the allergy itself, and it does not stop the histamine being released — it stops the message being received.
What happened in people
A mean Total 5 Symptoms Score of 7.87 against 8.68 on placebo in 580 adults, a difference of -0.89 (95% CI -1.33 to -0.45)
✎ 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 recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
That the single enantiomer works better in patients than the racemate — the two-fold affinity is exactly what removing an inactive enantiomer predicts, and the one registered head-to-head trial has no posted results
Where it acts
Nasal mucosa and dermal postcapillary venules — H1 receptors on vascular endothelium and on sensory nerve endings
Kind of result
The kind of result is not recorded
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · 6U5EA9RT2O · 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.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 128 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.
Comparator
A comparator is whatever the treatment was measured against.
A picture of it, and where the picture fails
It is like the other runner in a race.
Where that stops being true. A race has one winner. A study can show both arms improved.
What people get wrong. Results are read without asking what the other group got. Beating nothing is not beating a treatment.
The control condition against which the experimental intervention is assessed.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
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 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.
RQLQ overall score and Total 5 Symptoms Score over 4 weeks in persistent allergic rhinitis
All p<0.001 from week 1 through month 6; relative improvement over placebo exceeded the pre-defined 30% clinically meaningful threshold on all RQLQ scores
Repeated elsewhere
Partially Replicated
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. Predates trial registration, so there is no registry record against which the published analysis can be checked. 130 of 551 randomised patients did not complete.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
8.77 against 8.96 on placebo; ANCOVA mean difference -0.14 (95% CI -0.59 to 0.31), p=0.546
Repeated elsewhere
Failed to Replicate
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. Same sponsor, same design and same endpoint as NCT00653224, one week apart in size. The null result is visible only in the posted registry results.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
Interval reported. 95% CI -0
Written into the record, not signed off as a reviewed claim.
Cox hazard ratio 1.002 (95% CI 0.750 to 1.338), p=0.991
Repeated elsewhere
Failed to Replicate
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The safety and urticaria analyses were published as separate papers; the null primary asthma outcome appears only in the posted registry results. The 207-child extension trial NCT00160563 was terminated because of it.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Mean chronic idiopathic urticaria composite score over the first week of treatment
✓ The study showed what it set out to show
Who was studied
NCT00264303
How many people
886
Study design
Phase 4, randomised, double-blind, active-controlled against desloratadine
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
1.98 against 2.23 for desloratadine; ANCOVA net mean difference 0.25 (95% CI 0.08 to 0.43), p=0.005
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. Sponsored by the manufacturer of the winning drug, with no placebo arm, so the trial measures the gap between two active drugs and not the size of either effect.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Mean change from baseline in major symptom complex score 21 to 29 hours after dosing on day 2
✗ The study did not show it
Who was studied
NCT00544388
How many people
570
Study design
Phase 3, randomised, head-to-head against cetirizine in a pollen exposure chamber
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Not reported. The study completed in July 2004 and the registry record carries no posted results and no linked publication.
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. This is the one registered trial that directly tests the enantiomer against the racemate it was separated from, and its results are not public.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 6 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 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
Levocetirizine
What a person takes: Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL).
The measurement behind this step
Taken once daily in the evening in the registration trials. A high-fat meal delays peak concentration by about 1.25 hours and lowers peak by about 36% without changing total exposure, so it can be taken with or without food. The 5 mg oral solution is bioequivalent to the 5 mg tablet.
Getting in
Swallowed, absorbed fast, and mostly excreted unchanged
The tablet dissolves and the drug is in the bloodstream within about an hour. The liver barely touches it, which is why it has almost no interactions with other medicines.
──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
Peak plasma concentration is reached at about 0.9 hours after the tablet and 0.5 hours after the oral solution, with steady state after two days and an accumulation ratio of 1.12. Plasma protein binding is 91 to 92%. In vitro data indicate levocetirizine is unlikely to inhibit or induce hepatic drug-metabolising enzymes; the drug is largely excreted unchanged in urine.
The molecule carries opposing electrical charges at the same time, which makes it hard to cross into the brain. That is the design feature separating this generation of antihistamines from the older ones — though not perfectly, as the sleepiness figures show.
──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
At physiological pH the carboxylate is deprotonated and a piperazine nitrogen is protonated, giving a zwitterion with poor passive membrane permeability, and the molecule is additionally a substrate for P-glycoprotein efflux at the blood-brain barrier. Exclusion is partial rather than absolute: somnolence still occurred in 6% of adults on 5 mg against 2% on placebo, with dose ordering to 10 mg.
It occupies the histamine receptor and holds it switched off
The receptor histamine acts on flips between an on shape and an off shape by itself, even with no histamine around. This drug binds the off shape and locks it there, so the background signalling stops as well as the histamine-driven signalling.
──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
Levocetirizine is an inverse agonist rather than a neutral antagonist at HRH1: it preferentially stabilises the inactive receptor conformation and reduces constitutive Gq/11 signalling below baseline. Ki at the human H1 receptor is 3 nmol/L. The R-enantiomer carries essentially all of this activity; dextrocetirizine showed no clear inhibition of the human histamine wheal and flare.
Blood vessels stop leaking and nerve endings stop firing
With the receptor held off, small blood vessels in the nose and skin stop opening up and leaking fluid, and the itch nerves stop being triggered. The swelling, the running and the itching fall away together because they all came from the same switch.
╌╌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
H1 blockade on postcapillary venule endothelium prevents the phospholipase C, inositol trisphosphate and calcium cascade that drives nitric oxide release, vasodilatation and gap formation between endothelial cells; H1 blockade on unmyelinated C-fibre terminals prevents the depolarisation read as itch. In humans this is measured directly as suppression of the intradermal histamine wheal and flare, sustained for at least 24 hours after a 5 mg dose.
The measurable result is a lower total symptom score, roughly a tenth to a fifth off the untreated number. It is a real improvement in how the days feel, not a cure, and the allergy itself is untouched.
──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
In the 580-patient seasonal rhinitis trial the mean 24-hour reflective Total 5 Symptoms Score fell from 8.68 on placebo to 7.87 on treatment, a difference of -0.89 (95% CI -1.33 to -0.45). Nasal congestion is the symptom least affected, because it is driven substantially by leukotrienes and by late-phase cellular infiltration rather than by histamine at H1.
It does not stop the allergic reaction being set off, and it does not change what happens next. Giving it to allergic toddlers for eighteen months did not stop them developing asthma.
╌╌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
H1 antagonism acts downstream of IgE cross-linking and mast cell degranulation and leaves mediator release, eosinophil recruitment and the late-phase response substantially intact. EPAAC tested the disease-modification hypothesis directly in 514 sensitised infants over 18 months and returned a hazard ratio for asthma onset of 1.002 (95% CI 0.750 to 1.338).
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 6 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.
Adults and children from six months of age. It is one of a handful of second-generation antihistamines sold without a prescription in the United States since 2017.
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.
What the label states about particular groups
On pediatric, the label states: “The safety of XYZAL 5 mg once daily was evaluated in 243 pediatric patients 6 to 12 years of age in two placebo-controlled clinical trials lasting 4 and 6 weeks.”
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
On older people, the label states: “Clinical studies of XYZAL for each approved indication did not include sufficient numbers of patients aged 65 years and older to determine whether they respond differently than younger patients.”
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary Available data from published literature and postmarketing experience with levocetirizine use in pregnant women are insufficient to identify any drug-associated risks of miscarriage, birth defects, or adverse maternal or fetal outcomes.”
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary There are no data on the presence of levocetirizine in human milk, the effects on the breastfed infant, or the effects on milk production.”
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
On people with reduced liver function, the label states: “As levocetirizine is mainly excreted unchanged by the kidneys, it is unlikely that the clearance of levocetirizine is significantly decreased in patients with solely hepatic impairment [see Clinical Pharmacology ( 12.3 ) ] .”
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
On people with reduced kidney function, the label states: “XYZAL is known to be substantially excreted by the kidneys and the risk of adverse reactions to this drug may be greater in patients with impaired renal function.”
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
Where the result stopped carrying
NCT00621959, 596 adults, same design as the positive trial: mean difference -0.14 (95% CI -0.59 to 0.31), p=0.546
EPAAC, 514 sensitised toddlers over 18 months: hazard ratio for asthma onset 1.002 (95% CI 0.750 to 1.338), p=0.991
The EPAAC extension NCT00160563 was terminated after enrolling 207 children, the registry naming the null predecessor as the reason
Urinary retention and post-discontinuation pruritus were added to the label from postmarketing reports, not found in the registration programme
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 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 (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
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
Prescription only
❝ 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
Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
✎ 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
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
Taken once daily in the evening in the registration trials. 25 hours and lowers peak by about 36% without changing total exposure, so it can be taken with or without food. The 5 mg oral solution is bioequivalent to the 5 mg tablet.
✎ 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
Somnolence, fatigue and asthenia, dose-ordered across 2.5, 5 and 10 mg, with an explicit label warning against driving, operating machinery, and concurrent alcohol or CNS depressants. Postmarketing warnings for urinary retention and for new-onset pruritus within days of discontinuation after long-term use. A single 30 mg dose did not prolong QTc; multiple-dose QTc effects are stated as unknown. Cleared renally, so exposure rises in impaired kidney function. No clinically meaningful hepatic enzyme interactions were found in vitro, and no in vivo interaction studies were performed with levocetirizine itself.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
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
Oral tablet (5 mg) and oral solution (2.5 mg per 5 mL)
✎ 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
25 hours and lowers peak by about 36% without changing total exposure, so it can be taken with or without food. The 5 mg oral solution is bioequivalent to the 5 mg tablet.
✎ 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
Xyzal is oral at 3 DOSAGE FORMS AND STRENGTHS XYZAL oral solution is a clear, colorless liquid containing 0.5 mg of levocetirizine dihydrochloride per mL., recorded as fda label in effect 2025-07-22 in the United States.
US prescribing information · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · read 2026-08-30
Recorded price in US: 0.0517–0.22042 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 12 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
Recorded price in US: 0.16587 USD per one millilitre, across 3 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
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.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Levocetirizine 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 the single enantiomer works better in patients than the racemate — the two-fold affinity is exactly what removing an inactive enantiomer predicts, and the one registered head-to-head trial has no posted results
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 early antihistamine treatment of sensitised atopic infants prevents asthma — the ETAC subgroup that suggested it did not survive EPAAC
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 a second-generation antihistamine is non-sedating — the label warns against driving and against alcohol, and lists somnolence as the commonest cause of discontinuation
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 the positive seasonal rhinitis trial characterises the drug on its own — its identically designed twin was null
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.
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.
Formulation uncertainty
Several salts, forms or products of Levocetirizine are recorded. Results from one form may not transfer to another.
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.
A 0.89-point advantage over placebo on a five-symptom score in 580 adults
In plain words
In a two-week placebo-controlled trial in seasonal hay fever, people on the drug scored about nine-tenths of a point lower on a five-symptom scale than people on a dummy tablet. That is a real difference and a small one, and it is the size of effect this whole drug class produces.
What was measured
Mean 24-hour reflective Total 5 Symptoms Score over 14 days against placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A multi-centre, randomised, double-blind, placebo-controlled parallel-group study in 580 adults with seasonal allergic rhinitis reported a mean 24-hour reflective Total 5 Symptoms Score of 7.87 on levocetirizine 5 mg once daily against 8.68 on placebo over the full 14-day treatment period. The ANCOVA mean difference was -0.89 (95% CI -1.33 to -0.45), p<0.001. The T5SS sums sneezing, rhinorrhoea, nasal itching, nasal congestion and ocular itching, each rated 0 to 3, over morning and evening assessments.
Written into the record, not signed off as a reviewed claim
The twin trial, same design and 596 adults, found nothing
In plain words
The manufacturer ran a second trial with the same design, the same drug and slightly more people. It found no difference from the dummy tablet at all. The two trials sit side by side in the registry, and only one of them is the one usually quoted.
What was measured
Mean 24-hour reflective Total 5 Symptoms Score over 14 days against placebo — null
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
NCT00621959 was a multi-centre, randomised, double-blind, placebo-controlled parallel-group study of levocetirizine 5 mg once daily for two weeks in 596 adults with seasonal allergic rhinitis, with the same primary endpoint as NCT00653224. The mean 24-hour reflective Total 5 Symptoms Score was 8.77 on levocetirizine against 8.96 on placebo. The ANCOVA mean difference was -0.14 (95% CI -0.59 to 0.31), p=0.546. The confidence interval spans zero comfortably in both directions.
Written into the record, not signed off as a reviewed claim
EPAAC: 514 toddlers, 18 months of treatment, hazard ratio 1.002
In plain words
The largest and longest trial of this drug ever run asked whether giving it to allergic toddlers for a year and a half would stop them developing asthma. The answer was no, and it was not a near miss: the two groups were indistinguishable.
What was measured
Time to onset of asthma over 18 months of treatment, Cox hazard ratio
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Early Prevention of Asthma in Atopic Children study randomised 514 children aged 12 to 24 months with atopic dermatitis and sensitisation to grass pollen or house dust mite to levocetirizine 0.125 mg/kg twice daily or placebo for 18 months. The primary outcome, time to onset of asthma during treatment, gave a Cox hazard ratio of 1.002 (95% CI 0.750 to 1.338), p=0.991. First-quartile time to asthma onset was 10.3 months on levocetirizine and 9.5 months on placebo. The planned 18-month extension trial, NCT00160563, enrolled 207 children and was then terminated, with the registry recording the reason in plain words: the predecessor study did not show statistical significance in time to onset of asthma between the levocetirizine and placebo groups.
Source
NCT00152464 (EPAAC), posted registry results, UCB Pharma; termination reason recorded on NCT00160563
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
The subgroup that justified EPAAC came from ETAC, and EPAAC was built to confirm it and did not
In plain words
An earlier trial of the parent drug missed its main target but reported that a subgroup of allergic infants did better. That subgroup finding is what the next trial was designed around. The next trial enrolled exactly that subgroup, and the effect was gone.
What was measured
That early H1-antihistamine treatment of sensitised atopic infants prevents or delays asthma — an inference from an ETAC subgroup that the confirmatory trial specifically enrolling that subgroup did not reproduce
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Early Treatment of the Atopic Child study gave cetirizine 0.25 mg/kg twice daily or placebo to infants aged 1 to 2 years with atopic dermatitis for 18 months with 18 months of follow-up. There was no difference in cumulative prevalence of asthma in the intention-to-treat population (p=0.7). Infants sensitised to house dust mite or grass pollen were reported as significantly less likely to develop asthma on cetirizine over the treatment period (p=0.005 and p=0.002), sustained for the grass-pollen group at 36 months (p=0.008), and the authors wrote that further studies focusing specifically on sensitised groups were required to substantiate the finding. EPAAC was that study: it enrolled only children sensitised to grass pollen or house dust mite, used the active enantiomer, and returned a hazard ratio of 1.002. This is the textbook sequence in which a post-hoc subgroup survives one trial and does not survive the trial designed to test it.
Written into the record, not signed off as a reviewed claim
The two-fold receptor affinity is the marketing case, and the label calls it unknown
In plain words
The drug is one half of an older, cheaper drug. It binds the target twice as tightly as the mixture does, which is arithmetically what you would expect if the other half does nothing. Whether that translates into working better in a person has never been shown.
What was measured
That the single enantiomer relieves symptoms better than the racemate it was separated from — an in vitro affinity ratio presented as a therapeutic advantage, with the one registered head-to-head trial unreported
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Xyzal label records an in vitro human H1 receptor affinity of Ki = 3 nmol/L for levocetirizine against 6 nmol/L for cetirizine, and states in the following sentence that the clinical relevance of this finding is unknown. A racemate containing 50% inactive enantiomer would show exactly a two-fold lower apparent affinity by mass, so the number is consistent with the enantiomer being no more potent per molecule than it already was inside the racemate. UCB completed a 570-subject randomised head-to-head of levocetirizine against cetirizine in a controlled ragweed exposure chamber in July 2004 (NCT00544388) with a primary endpoint of major symptom complex change 21 to 29 hours after dosing; the registry record carries no posted results and no linked publication.
Source
XYZAL prescribing information, section 12.1 Mechanism of Action (NDA 022064); NCT00544388 registry record, UCB Pharma, completed July 2004, no results posted
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
It beat desloratadine in chronic hives by a quarter of a point
In plain words
A large head-to-head trial in long-running hives found this drug slightly better than its main rival. The difference was statistically solid and clinically small: a quarter of a point on a scale where the average score was about two.
What was measured
Mean chronic idiopathic urticaria composite score over week 1, levocetirizine against desloratadine
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A randomised, double-blind Phase 4 study in 886 patients with chronic idiopathic urticaria compared levocetirizine 5 mg with desloratadine 5 mg, both once daily in the morning. The mean CIU composite score over the first week of treatment was 1.98 on levocetirizine against 2.23 on desloratadine, an ANCOVA net mean difference of 0.25 (95% CI 0.08 to 0.43), p=0.005. Separately, a pooled analysis of two placebo-controlled urticaria trials in 294 patients reported an additional 6.5 pruritus-free days per 30-day month on levocetirizine against placebo (95% CI 3.8 to 9.3, p<0.001).
Written into the record, not signed off as a reviewed claim
It is sedating in a measurable, dose-related way, and two warnings arrived after approval
In plain words
Sleepiness was three times more common on the drug than on the dummy tablet, and it got worse as the dose went up. Two further problems — difficulty passing urine, and severe itching on stopping after long use — were only found once the drug was on the market.
What was measured
Somnolence incidence against placebo across eight controlled trials in 1,896 subjects
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Across eight placebo-controlled trials in 1,896 adults and adolescents, somnolence was reported by 61 of 1,070 subjects (6%) on 5 mg and 22 of 421 (5%) on 2.5 mg against 16 of 912 (2%) on placebo, with clear dose ordering across 2.5, 5 and 10 mg. It was the commonest adverse reaction leading to discontinuation (0.5%). The label warns against hazardous activity requiring alertness and against concurrent alcohol or CNS depressants. Two further Warnings and Precautions entries derive from postmarketing reports rather than trials: urinary retention, with advice to discontinue if it occurs, and new-onset pruritus within days of stopping after months-to-years of use, which the label notes may improve on restarting or tapering.
Source
XYZAL prescribing information, sections 5.1, 5.2, 5.3 and Table 1 of 6.1 Clinical Trials Experience (NDA 022064)
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
Six months of treatment improved quality of life, in the trial designed to test it
In plain words
A six-month trial in people with year-round allergy measured how much the illness interfered with daily life, not just symptom counts. The drug improved that measure by more than the pre-agreed threshold for a difference patients would notice.
What was measured
RQLQ overall score and Total 5 Symptoms Score over 6 months against placebo in 551 patients
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Xyzal in Persistent Rhinitis Trial randomised 551 adults sensitised to both grass pollen and house dust mite to levocetirizine 5 mg daily or placebo for six months, with 421 completing. Co-primary endpoints were the Rhinoconjunctivitis Quality of Life Questionnaire overall score and the Total 5 Symptoms Score over four weeks; both improved significantly from week 1 through month 6 (all p<0.001). The relative improvement over placebo exceeded the pre-defined 30% threshold for clinical meaningfulness on all RQLQ scores, and improvement from baseline was three times the established minimal important difference. SF-36 physical and mental summary scores also improved (p<=0.004).
This order is fixed in code and does not count clicks or time on the page.
What is not here
8 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
How this medicine reached us — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
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.
The active left-handed half of cetirizine, an H1 receptor inverse agonist that holds the histamine receptor in its resting shape rather than merely blocking histamine from reaching it — it lowered a five-symptom seasonal allergy score by 0.89 points against placebo in 580 adults (95% CI -1.33 to -0.45, p<0.001), produced no measurable benefit at all in a 596-adult trial of identical design (p=0.546), and completely failed the 514-child EPAAC trial that tested whether it prevents asthma (hazard ratio 1.002, 95% CI 0.750 to 1.338, p=0.991).
Recorded evidence blocks (10)
Q1
On the Levocetirizine label: indicated for what?
"XYZAL is a histamine H 1 -receptor antagonist indicated for: The relief of symptoms associated with perennial allergic rhinitis ( 1.1 ) The treatment of the uncomplicated skin manifestations of chronic idiopathic urticaria ( 1.2 ) 1.1 Perennial Allergic Rhinitis XYZAL is indicated for the relief of symptoms associated…": indications and usage on Levocetirizine's label. DailyMed label · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · 2025-07-22
Q2
119 registered trials of Levocetirizine — at which phases?
Registered studies posting no result
89 of 119
119 registered studies of Levocetirizine: 42 phase4, 30 phase3, 22 phase1, 16 phase2, 7 na, 4 na or unstated, 1 early phase1. CLINICALTRIALS_SNAPSHOT · 2026-09-01
135 with a PubMed record
Show the evidence
phase4
42
phase3
30
phase1
22
phase2
16
na
7
na or unstated
4
6 more recorded rows
early phase1
1
completed
102
terminated
8
not yet recruiting
3
recruiting
3
unknown
3
recorded 2026-09-01 · last checked 2026-09-04
Q3
8 of Levocetirizine's trials stopped: safety, accrual/recruitment, funding/business, other?
safety (2), accrual/recruitment (1), funding/business (1) and other (4): Levocetirizine's stop wording, clustered. CLINICALTRIALS_SNAPSHOT · 2026-09-01
"The predecessor study A00309 (NCT00152464) did not show statistical significance in time to onset of asthma between the levocetirizine and placebo groups."; 8 of 119 registered studies
Show the evidence
Trial
NCT00160563
terminated; "The predecessor study A00309 (NCT00152464) did not show statistical significance in time to onset of asthma between the levocetirizine and placebo groups."
NCT00751166
terminated; "Study could not be re-supplied with study medication in a timely manner."
NCT01008592
terminated; "Mediators of interest were not consistently detectable with the analytical methods employed."
NCT01825655
terminated; "Unable to recruit patients"
NCT01981499
terminated; "The trial was prematurely terminated on 01April2014 due to safety concerns."
NCT04990388
terminated; "Sponsor decision not related to safety concerns"
2 further recorded trials
NCT05095311
terminated; "The recruited population was no longer made available to participate in the study."
NCT05946551
terminated; "Study was terminated due to lack of funding."
recorded 2026-09-01 · last checked 2026-09-04
Q4
Human studies of Levocetirizine used Levocetirizine 1.25 mg — over how long?
Human studies of Levocetirizine used "Levocetirizine 1.25 mg". ClinicalTrials.gov · 2026-09-01
13 recorded entries; human; tablet; also "Cetirizine HCl Tablets 10 mg", "Cetirizine Hydrochloride 10 mg tablet", "Cetirizine (10mg)"
Show the evidence
human
NCT00628108
Levocetirizine 1.25 mg
NCT00649857
Cetirizine HCl Tablets 10 mg
NCT00776022
tablet; Cetirizine Hydrochloride 10 mg tablet
NCT00851344
Cetirizine (10mg)
NCT00863902
Cetirizine Hydrochloride 10 mg tablets, single dose
NCT00972504
Cetirizine 10mg
7 more recorded rows
humanNCT01318681
cetirizine 10 mg
humanNCT01557439
Levocetirizine Dihydrochloride 5 mg Tablets
humanNCT01567501
Levocetirizine Dihydrochloride tablets 5 mg
humanNCT01981499
10 mg cetirizine
humanNCT03047278
Cetirizine Hydrochloride 10 mg
humanNCT03772158
Cetirizine 10 mg
humanNCT04293822
Cetirizine 1% Gel
recorded 2026-09-01 · last checked 2026-09-04
Q5
Levocetirizine's half-life is 8 to 9 hours — which schedules were studied?
8 to 9 hours, the half-life Levocetirizine's label states: "Elimination The plasma half-life in adult healthy subjects was about 8 to 9 hours after administration of oral tablets and oral solution, and the mean oral total body clearance for levocetirizine was approximately 0.63 mL/kg/min." DailyMed label · 1673f7ff-0c7c-4403-86cf-c05eb1475222 · 2025-07-22
tmax 0.9 hour.
Show the evidence
half lifepharmacokinetics
8 to 9 hours; Elimination The plasma half-life in adult healthy subjects was about 8 to 9 hours after administration of oral tablets and oral solution, and the mean oral total body clearance for levocetirizine was approximately 0.63 mL/kg/min.
tmaxpharmacokinetics
0.9 hour; In adults, peak plasma concentrations are achieved 0.9 hour after administration of the oral tablet.
metabolismpharmacokinetics
Metabolism The extent of metabolism of levocetirizine in humans is less than 14% of the dose and therefore differences resulting from genetic polymorphism or concomitant intake of hepatic drug metabolizing enzyme inhibitors are expected to be negligible.
recorded 2025-07-22 · last checked 2026-09-04
Q6
Which 72 trials of Levocetirizine posted no result?
Posted no result
72 of 72 completed trials
Registrations
NCT02932774, NCT00542607, NCT00649857, NCT00650065, NCT00520754 and NCT00639587, and 66 more
Completion dates
oldest 2001-07; newest 2024-03-01
Show the evidence
Trial
NCT02932774
2001-07
NCT00542607
2002-12
NCT00649857
2002-12
NCT00650065
2002-12
NCT00520754
2003-03
NCT00639587
2003-03
14 further recorded trials
NCT00521131
2003-05
NCT00794846
2003-05
NCT00794495
2003-07
NCT00794599
2003-08
NCT00525278
2003-10
NCT00524836
2004-02
NCT00525382
2004-03
NCT00789152
2004-05-01
NCT00521040
2004-07
NCT00544388
2004-07
NCT00150761
2004-10
NCT00794378
2004-11
NCT00794794
2004-11
NCT00152412
2004-12
Q7
At the median, Levocetirizine's trials enrolled 60 people — anything larger?
Median enrolment
60
Largest enrolment
10728
Registered trials counted
118
Q8
What do 359 spontaneous reports say about Levocetirizine — 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.
Levocetirizine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 359 reaction mentions were counted: somnolence 72; urticaria 52; drug-induced liver injury 44; loss of consciousness 42. FAERS via Open Targets · CHEMBL1201190 · 2026-06-24
Show the evidence
somnolence
72
urticaria
52
drug-induced liver injury
44
loss of consciousness
42
angioedema
30
abortion spontaneous
29
4 more recorded rows
anaphylactic reaction
28
face oedema
24
altered state of consciousness
19
erythema multiforme
19
recorded 2026-06-24 · last checked 2026-09-04
Q9
Which 10 reactions does Levocetirizine's label not list?
Dealkylation pathways are primarily mediated by CYP3A4 while aromatic oxidation involves multiple and/or unidentified CYP isoforms.
pharmacokinetics
Levocetirizine at concentrations well above C max level achieved within the therapeutic dose ranges is not an inhibitor of CYP isoenzymes 1A2, 2C9, 2C19, 2A1, 2D6, 2E1, and 3A4, and is not an inducer of UGT1A or CYP isoenzymes 1A2, 2C9 and 3A4.
clinical_pharmacology
Dealkylation pathways are primarily mediated by CYP3A4 while aromatic oxidation involves multiple and/or unidentified CYP isoforms.
clinical_pharmacology
Levocetirizine at concentrations well above C max level achieved within the therapeutic dose ranges is not an inhibitor of CYP isoenzymes 1A2, 2C9, 2C19, 2A1, 2D6, 2E1, and 3A4, and is not an inducer of UGT1A or CYP isoenzymes 1A2, 2C9 and 3A4.
ChEMBL 37 — CC BY-SA 3.0 Unported · ClinicalTrials.gov — US Government work · Open Targets 26.06 — CC0 · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 6 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.