This page shows what was measured, who it was measured in, and what that does not settle.
What Cetirizine does in the body
Hay fever, allergic sneezing and itching, and long-running hives
When you meet something you are allergic to, cells in your nose and skin dump histamine into the tissue around them. Histamine makes vessels leak and nerves fire, which is the sneeze, the runny nose, the itch and the hive. Cetirizine gets to the receptor first and sits in it, so the histamine arrives and finds nowhere to dock. It is designed to stay outside the brain, and it mostly does — but not entirely, which is why some people find it makes them sleepy.
What happened in people
Complete suppression of chronic spontaneous urticaria 2.72 times as often as placebo at 10 mg daily (95% CI 1.51 to 4.91)
✎ 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.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
That it helps a common cold, when the randomised evidence shows a two-day effect and nothing after that, and nothing at all in children
Where it acts
H1 receptors on blood vessels, sensory nerve endings and mucosal tissue in the nose, eyes and skin
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
Its recorded molecular formula is C21H25ClN2O3•2HCl, weighing 461.82.
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
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 119 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.
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.
Formulation
A formulation is the exact made-up form a substance comes in.
A picture of it, and where the picture fails
It is like the difference between a whole bean and instant coffee.
Where that stops being true. Coffee tastes different. A formulation can change how much reaches the blood.
What people get wrong. Two products with the same name are assumed to behave the same. They often do not.
The specific composition and physical form of a product, including salt, excipients and release profile.
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.
Proportion of participants with complete suppression of urticaria, and good or excellent response
✓ The study showed what it set out to show
Who was studied
Cochrane H1-antihistamines for chronic spontaneous urticaria (CD006137.pub2)
How many people
9759
Study design
Systematic review and meta-analysis of 73 randomised trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Cetirizine 10 mg daily against placebo for complete suppression, RR 2.72 (95% CI 1.51 to 4.91); loratadine 10 mg against cetirizine 10 mg, RR 1.05 (95% CI 0.76 to 1.43)
Repeated elsewhere
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. Only 34 of the 73 identified studies provided usable data across 23 comparisons, and the intervention durations ran to at most three months. Chronic urticaria frequently lasts years, and none of this evidence describes that timescale.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications
Interval reported. 95% CI 1
Written into the record, not signed off as a reviewed claim.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
No difference in the intention-to-treat population, p=0.7; house dust mite-sensitised subgroup p=0.005 and grass pollen-sensitised subgroup p=0.002 over the 18 treatment months, grass pollen sustained to 36 months at p=0.008
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. Insomnia was more frequent on cetirizine than placebo over 18 months, 9.0% against 5.3%, and children aged 6 to 11 months on cetirizine showed greater irritability and fussiness than those on placebo in a separate week-long study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
Severity of overall cold symptoms, antihistamine monotherapy against placebo
✗ The study did not show it
Who was studied
Cochrane antihistamines for the common cold (CD009345.pub2)
How many people
4342
Study design
Systematic review and meta-analysis of 18 randomised trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Day one or two: 45% beneficial effect against 38%, OR 0.74 (95% CI 0.60 to 0.92); no difference at three to four days or six to ten days
Repeated elsewhere
Replicated
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. Effects on individual symptoms were statistically detectable and judged clinically non-significant by the reviewers. Only two trials included children, with conflicting results, and the review concluded there is no evidence of effectiveness in children.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
Two perennial rhinitis trials showed significant reductions in symptoms for up to 8 weeks; two 4-week urticaria trials showed significant improvement; 10 mg more effective than 5 mg and 20 mg gave no added effect
Repeated elsewhere
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. The label reports the outcome of these trials qualitatively rather than as effect sizes with confidence intervals, so the magnitude of the rhinitis benefit cannot be read off the document the way the urticaria dose-response can.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
RNAWiki holds 4 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
Cetirizine
What a person takes: Oral, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications.
The measurement behind this step
Rapidly absorbed with Tmax about 1 hour and comparable bioavailability between tablet and solution. Food does not change total exposure but delays Tmax by 1.7 hours and reduces Cmax by 23%. Metabolism is limited — oxidative O-dealkylation to a metabolite with negligible antihistaminic activity, by an enzyme the label says has not been identified — so about half the dose is excreted unchanged in urine and dose reduction is required in renal impairment.
Getting in
A tablet built to stay out of the brain
Cetirizine is what the body makes when it breaks down an older, very sedating antihistamine. The change that happens in that breakdown is what keeps it mostly out of the brain.
──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
Cetirizine is the carboxylic acid metabolite of hydroxyzine. The terminal carboxylate makes the molecule zwitterionic at physiological pH and sharply reduces passive blood-brain barrier permeation. Absorbed rapidly with Tmax about 1 hour, mean Cmax 311 ng/mL after ten days of 10 mg once daily, plasma protein binding 93%, linear kinetics from 5 to 60 mg, no accumulation.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
The allergen has landed, the mast cell has emptied, and histamine is diffusing into the tissue. The drug does not stop any of that.
╌╌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
Allergen cross-links IgE bound to FcεRI on mast cells and basophils, triggering degranulation within seconds. Cetirizine has no effect on degranulation; it competes for the receptor downstream of it, which is why it works better taken before an exposure than during one.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
Cetirizine sits in the H1 receptor on blood vessels and nerve endings, so histamine arrives and finds no free receptor.
╌╌Measured in animals. A result in animals says what to test next. It does not say what happens in people.
The measurement behind this step
Selective inhibition of peripheral H1 receptors. In vitro receptor binding showed no measurable affinity for receptors other than H1, and animal models showed negligible anticholinergic and antiserotonergic activity — though the label records that dry mouth was nonetheless more common than placebo in clinical studies.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
Leak, itch and sneeze are switched off; blockage is not
Vessels stop leaking and sensory nerves stop firing, so the runny nose, itch, sneeze and hive settle. The blocked nose, which histamine contributes little to, largely does not.
╌╌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 prevents histamine-driven endothelial gap formation, vasodilation and sensory C-fibre activation. Nasal congestion is dominated by late-phase cellular infiltration and by mediators other than histamine, which is the pharmacological reason an intranasal corticosteroid outperforms an oral antihistamine for that symptom.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
For chronic hives the measured result is complete clearance about 2.7 times as often as on a dummy tablet.
╌╌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
Cetirizine 10 mg daily against placebo for complete suppression of chronic spontaneous urticaria: RR 2.72 (95% CI 1.51 to 4.91), short and intermediate term. Registration data: 10 mg more effective than 5 mg, 20 mg no added effect.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · a recorded source, not a stored snapshot
Not enough to sedate most people, and enough to sedate some. The carton says so even though the animal studies said it would not.
╌╌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
Paediatric somnolence was dose-related at 1.3% placebo, 1.9% at 5 mg and 4.2% at 10 mg, against animal data showing negligible brain penetration and no significant cerebral H1 occupancy. The over-the-counter Drug Facts warn that drowsiness may occur, that alcohol and sedatives increase it, and to be careful driving.
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · 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 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.
People with hay fever and other allergic rhinitis, and people with chronic hives. It is sold without prescription and taken by tens of millions of people who never see a clinician about it.
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 and efficacy of QUZYTTIR in patients less than 6 months of age has not been established.”
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
On older people, the label states: “In clinical trials with QUZYTTIR, 18 patients were 65 years and older, and 6 patients were 75 years and older.”
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary There are no adequate and well-controlled studies in pregnant women with cetirizine hydrochloride the active ingredient in QUZYTTIR.”
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary Cetirizine hydrochloride has been reported to be present in human breast milk.”
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
On people with reduced liver function, the label states: “No dosage adjustment is required in patients with hepatic impairment.”
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
On people with reduced kidney function, the label states: “No dosage adjustment is required in patients with moderate and severe renal impairment and in patients on dialysis.”
US prescribing information · f33e859d-ebc9-4d4f-a57d-204c48760d20 · read 2026-08-30
Where the result stopped carrying
The primary intention-to-treat endpoint of ETAC: no difference in cumulative asthma prevalence at 36 months (p=0.7)
Insomnia and irritability, not sedation, were the signals in the infant trials
No clinically significant effect on nasal obstruction, rhinorrhoea or sneezing in the common cold at any timepoint
A postmarketing entry for new-onset pruritus days after stopping the drug, with no mechanism offered anywhere in the label
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.
A different form was studied
The studied form is not the form on the shelf.
On this record: This record is linked to 1 related forms. Evidence does not carry across all of them.
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)
It was studied for a different goal
The studies measured something else entirely. 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, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications
✎ 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
Rapidly absorbed with Tmax about 1 hour and comparable bioavailability between tablet and solution. 7 hours and reduces Cmax by 23%.
✎ 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. The rest of the recorded wording: Metabolism is limited — oxidative O-dealkylation to a metabolite with negligible antihistaminic activity, by an enzyme the label says has not been identified — so about half the dose is excreted unchanged in urine and dose reduction is required in renal impairment.
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
Drowsiness may occur and the over-the-counter carton says so, with warnings to avoid alcohol and to be careful driving. Contraindicated in anyone who has reacted to hydroxyzine, its parent compound. Dose-related somnolence in children; insomnia and irritability reported in infants. Transient reversible transaminase elevations occur; hepatitis with significant transaminase and bilirubin elevation has been reported. Rare but potentially severe postmarketing events include anaphylaxis, convulsions, cholestasis, hepatitis, glomerulonephritis, haemolytic anaemia, thrombocytopenia, severe hypotension, acute generalised exanthematous pustulosis, suicidal ideation and suicide, and new-onset pruritus within a few days of discontinuation after long-term use.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Where this came from
Cetirizine hydrochloride United States prescribing information — Indications, Clinical Pharmacology (mechanism, absorption, distribution, metabolism, elimina… · 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
Oral, once daily: tablets, chewable tablets, orally disintegrating tablets, oral solution and syrup, from 6 months of age in the paediatric indications
✎ 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
7 hours and reduces Cmax by 23%.
✎ 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. The rest of the recorded wording: Metabolism is limited — oxidative O-dealkylation to a metabolite with negligible antihistaminic activity, by an enzyme the label says has not been identified — so about half the dose is excreted unchanged in urine and dose reduction is required in renal impairment.
No source is stored against this line.
What is recorded as being sold
496 products list this as an active ingredient in the United States drug directory. 464 of them contain it and nothing else.
FDA National Drug Code directory · 71335-9612 · read 2026-08-29
They are sold as capsule, capsule, liquid filled, for solution, injection, powder and solution, taken intravenous, ophthalmic and oral.
FDA National Drug Code directory · 71335-9612 · read 2026-08-29
The regulator's established pharmacologic class for it is histamine h1 receptor antagonists [moa] and histamine-1 receptor antagonist [epc].
FDA National Drug Code directory · 71335-9612 · read 2026-08-29
431 published labels name it as an active ingredient. 400 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 9abdae64-4c3d-47f3-8224-fc81f7bfe557 · read 2026-08-29
Those labels are classed as human otc drug and human prescription drug.
US prescribing information · 9abdae64-4c3d-47f3-8224-fc81f7bfe557 · read 2026-08-29
Recorded price in US: 0.02278–0.44679 USD per one millilitre, across 18 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: 0.05172–2.09088 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 37 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.
Evidence on this page does not automatically apply to this one.
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 Cetirizine 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 cetirizine is non-sedating, inferred from rat autoradiography and mouse receptor occupancy while its own carton warns about driving
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 it helps a common cold, when the randomised evidence shows a two-day effect and nothing after that, and nothing at all in children
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 allergen-specific subgroups in ETAC identify a population in whom asthma can be prevented, on subgroup analyses the authors said needed confirming and that were never confirmed
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 fourfold up-dosing in chronic urticaria follows from the drug’s own dose-ranging data, which found no added effect at twice the licensed dose
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 Cetirizine 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.
In chronic hives it clears the rash almost three times as often as placebo
In plain words
For long-running hives with no identifiable cause, the pooled randomised evidence puts complete clearance at 2.72 times the placebo rate at the standard 10 mg dose.
What was measured
Proportion of participants with complete suppression of urticaria, cetirizine 10 mg against placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Cochrane review of H1 antihistamines for chronic spontaneous urticaria identified 73 studies in 9,759 participants, of which 34 provided data across 23 comparisons. Cetirizine 10 mg once daily produced complete suppression of urticaria more often than placebo both in the short term and at up to three months: RR 2.72 (95% CI 1.51 to 4.91). Loratadine 10 mg against cetirizine 10 mg gave RR 1.05 (95% CI 0.76 to 1.43) for complete suppression — no detectable difference between them. The cetirizine label supports the dose choice from its own registration programme: two 4-week randomised placebo-controlled trials in chronic idiopathic urticaria showed significant improvement, the 10 mg dose was more effective than 5 mg, and 20 mg gave no added effect.
Written into the record, not signed off as a reviewed claim
The non-sedating claim is made in rodents and contradicted on the carton
In plain words
Cetirizine is sold as a second-generation, non-drowsy antihistamine. Its own over-the-counter box tells you drowsiness may occur and to be careful driving. Loratadine’s box does not, and fexofenadine’s carries no drowsiness warning at all.
What was measured
That cetirizine is a non-sedating antihistamine because rodent studies show negligible brain penetration — a species-level inference the human label declines to make
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Clinical Pharmacology section supports low central activity with animal data: autoradiographic studies with radiolabelled cetirizine in the rat showed negligible penetration into the brain, and ex vivo experiments in the mouse showed that systemically administered cetirizine does not significantly occupy cerebral H1 receptors. The human evidence points the other way. The over-the-counter Drug Facts for cetirizine read, under When using this product: drowsiness may occur; avoid alcoholic drinks; alcohol, sedatives and tranquilizers may increase drowsiness; be careful when driving a motor vehicle or operating machinery. The corresponding loratadine Drug Facts read only: do not take more than directed; taking more than directed may cause drowsiness. Paediatric trial data show the dose-response the animal work would not predict: somnolence 1.3% on placebo, 1.9% at 5 mg, 4.2% at 10 mg. The generational label — first-generation sedating, second-generation non-sedating — turns out to describe a gradient rather than a category, and cetirizine sits at the sedating end of the second generation.
Source
Cetirizine hydrochloride United States prescribing information, Clinical Pharmacology and Adverse Reactions; over-the-counter Drug Facts labelling for cetirizine, loratadine and fexofenadine (openFDA SPL)
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
A drug for itching that can cause itching when it is stopped
In plain words
Years after approval, the label gained a postmarketing entry: severe new itching starting within a few days of stopping cetirizine, in people who had taken it for months or years.
What was measured
Presence and wording of the discontinuation-pruritus entry in the postmarketing section, against the original approval label
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The postmarketing experience section of the cetirizine label now lists, among rare but potentially severe events, new-onset pruritus within a few days after discontinuation of cetirizine, usually after long-term use of a few months to years. This was not in the original approval and is not explained by the drug’s pharmacology as described elsewhere in the same document: an H1 antagonist with an 8.3-hour half-life and no receptor affinity beyond H1 has no obvious mechanism for a withdrawal syndrome, and the label offers none. The practical consequence is a trap for both patient and clinician: the itch that appears on stopping looks exactly like the condition returning, and treating it by restarting the drug both relieves it and perpetuates it.
Source
Cetirizine hydrochloride United States prescribing information, Adverse Reactions — Post-Marketing Experience
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
It did not prevent asthma, and the subgroups that worked were found afterwards
In plain words
A large trial gave cetirizine to infants with eczema for eighteen months to see whether it would stop them developing asthma. Across everyone randomised, it made no difference. Two allergen-specific subgroups did separate, and no confirmatory trial was ever run.
What was measured
Cumulative prevalence of asthma at 36 months in the intention-to-treat population, and in prespecified allergen-sensitised subgroups
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Early Treatment of the Atopic Child study randomised infants aged 1 to 2 years with atopic dermatitis to cetirizine 0.25 mg/kg twice daily or placebo for 18 months, with a further 18 months of follow-up after treatment stopped — a design chosen specifically to distinguish suppression from prevention. In the intention-to-treat population there was no difference in cumulative prevalence of asthma (p=0.7). Infants sensitised to house dust mite or grass pollen treated with cetirizine were significantly less likely to develop asthma over the 18 treatment months (p=0.005 and p=0.002), and the grass-pollen effect was sustained across the full 36 months (p=0.008) while the house dust mite difference narrowed. The authors concluded that further studies focusing specifically on sensitised groups were required to substantiate the finding. They were not done, and no preventive indication exists. The same trial produced an adverse signal worth keeping: over 18 months, insomnia was more frequent on cetirizine than placebo, 9.0% against 5.3% — the opposite of the drug’s reputation.
Written into the record, not signed off as a reviewed claim
For a cold it works for two days and then stops working
In plain words
Antihistamines are sold for colds all over the world. In eighteen randomised trials the benefit lasted through days one and two and had vanished by day three, and in children there was no benefit at all.
What was measured
Proportion with a beneficial effect on overall cold symptom severity, by day of treatment
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Cochrane review of antihistamines as monotherapy for the common cold included 18 randomised trials reported in 17 publications, with 4,342 participants of whom 212 were children, in both natural and experimentally induced colds; trials in patients with an allergic component were excluded. On day one or two, 45% had a beneficial effect on overall symptom severity against 38% on placebo, odds ratio 0.74 (95% CI 0.60 to 0.92). There was no difference at three to four days or at six to ten days. On individual symptoms, sedating antihistamines produced small effects the reviewers judged clinically non-significant — rhinorrhoea on day three, mean difference -0.23 (95% CI -0.39 to -0.06) on a four- or five-point scale; sneezing on day three, -0.35 (95% CI -0.49 to -0.20) on a four-point scale. Only two trials included children and the results conflicted. The reviewers concluded there is no evidence of effectiveness in children.
Written into the record, not signed off as a reviewed claim
Guidelines quadruple a dose the label says gave no added effect
In plain words
For stubborn hives, specialists routinely go to four times the standard dose. The registration trials that set that standard dose found that doubling it added nothing.
What was measured
That doses above 10 mg add clinical benefit in chronic urticaria, when the drug’s own dose-ranging programme found 20 mg gave no added effect
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The cetirizine label reports from its chronic idiopathic urticaria programme that the 10 mg dose was more effective than 5 mg and that the 20 mg dose gave no added effect. The international EAACI/GA²LEN/EuroGuiDerm/APAAACI urticaria guideline nonetheless recommends increasing a second-generation antihistamine to up to fourfold the licensed dose before adding another agent, in patients not controlled at the standard dose. Both positions can be defensible — a flat dose-response averaged across a registration population does not exclude a benefit in the non-responder subgroup a guideline is written about — but the reader should know that the up-dosing recommendation rests on later trials and expert consensus rather than on the dose-ranging data in the label, and that above the licensed dose the sedation warning on the carton applies with more force, not less.
Written into the record, not signed off as a reviewed claim
How many documents were read
393 documents were read for this substance.
RNAWiki source record
20 of them state the same proteinBinding, and they agree.
RNAWiki source record
Where else this substance is registered
FDA substance identifier (UNII)
64O047KTOA
CAS registry number
83881-51-0
PubChem compound
2678
RxNorm concept
203150
Checks this page had to pass
✓ Passed
Identity resolved
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no quarantine open
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Every public sentence names a source
The opening statement carries the origin: Written into the record, not signed off.
✗ Not passed
Trial roles classified for highlighted evidence
No registered study is classified as testing this substance.
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No internal keys in reader text
enforced by the copy-contract test over the rendered page
✗ Not passed
Safety mode resolved
No register row and no identity class settled the question.
✓ Passed
Canonical metadata present
slug and display name present
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.
Withdrawn in United States, 2026, for "Cross Contamination with Other Products: Customer complaints for appearance of discolored tablets and red dots observed on Cetirizine Hydrochloride Tablets USP 5 mg. Determined to be Ranitidine." (openFDA drug enforcement Class I recall)
What the approval register records
79 approved applications cover products containing this substance. The earliest was NDA019835, approved 19951208 to KENVUE BRANDS.
This order is fixed in code and does not count clicks or time on the page.
What is not here
7 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.
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.
A peripherally selective H1 antihistamine that produced complete suppression of chronic spontaneous urticaria 2.72 times as often as placebo in the Cochrane comparison, whose own over-the-counter carton warns that drowsiness may occur and to be careful driving — a warning its rival loratadine does not carry — and whose label now records new-onset itching within days of stopping it after long-term use.
Recorded evidence blocks (9)
Q1
On the Cetirizine label: indicated for what?
"QUZYTTIR ® is indicated for the treatment of acute urticaria in adults and children 6 months of age and older. QUZYTTIR ® is a histamine-1 (H 1 ) receptor antagonist indicated for the treatment of acute urticaria in adults and children 6 months of age and older ( 1 ) Limitations of Use : Not recommended in pediatric…": indications and usage on Cetirizine's label. DailyMed label · 573770f6-b76e-f6ba-e063-6294a90aa54d · 2026-07-31
Q2
75 registered trials of Cetirizine — at which phases?
Registered studies posting no result
54 of 75
75 registered studies of Cetirizine: 23 phase4, 17 phase1, 16 phase3, 11 phase2, 6 na, 4 na or unstated, 1 early phase1. CLINICALTRIALS_SNAPSHOT · 2026-09-01
494 with a PubMed record
Show the evidence
phase4
23
phase1
17
phase3
16
phase2
11
na
6
na or unstated
4
7 more recorded rows
early phase1
1
completed
60
terminated
6
unknown
4
recruiting
2
withdrawn
2
not yet recruiting
1
recorded 2026-09-01 · last checked 2026-09-04
Q3
8 of Cetirizine's trials stopped: safety, accrual/recruitment, funding/business, other?
safety (2), accrual/recruitment (2), funding/business (1) and other (3): Cetirizine's stop wording, clustered. CLINICALTRIALS_SNAPSHOT · 2026-09-01
"Study could not be re-supplied with study medication in a timely manner."; 8 of 75 registered studies
Show the evidence
Trial
NCT00751166
terminated; "Study could not be re-supplied with study medication in a timely manner."
NCT00927329
withdrawn; "Original PI left institution."
NCT01825655
terminated; "Unable to recruit patients"
NCT01981499
terminated; "The trial was prematurely terminated on 01April2014 due to safety concerns."
NCT04836806
withdrawn; "Study stopped due to issues with enrollment and lack of funding."
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 Cetirizine used Cetirizine HCl Tablets 10 mg — over how long?
Human studies of Cetirizine used "Cetirizine HCl Tablets 10 mg". ClinicalTrials.gov · 2026-09-01
17 recorded entries; human; tablet; also "Zyrtec® 10 mg", "Zyrtec® Tablets 10 mg", "Cetirizine Hydrochloride 10 mg tablet"
Show the evidence
human
NCT00649857
Cetirizine HCl Tablets 10 mg
NCT00649857
Zyrtec® 10 mg
NCT00650065
Zyrtec® Tablets 10 mg
NCT00776022
tablet; Cetirizine Hydrochloride 10 mg tablet
NCT00851344
Cetirizine (10mg)
NCT00863902
Cetirizine Hydrochloride 10 mg tablets, single dose
11 more recorded rows
humanNCT00863902
Zyrtec® 10 mg tablets, single dose
humanNCT00972504
Cetirizine 10mg
humanNCT01064102
Zyrtec Tablets 10 mg
humanNCT01318681
cetirizine 10 mg
humanNCT01981499
10 mg cetirizine
humanNCT03047278
Cetirizine Hydrochloride 10 mg
humanNCT03772158
Cetirizine 10 mg
humanNCT03772158
ZYRTEC 10 mg
humanNCT04071821
tablet; Zyrtec tablet 10mg
humanNCT04189588
Cetirizine HCl 10 mg/mL
humanNCT04293822
Cetirizine 1% Gel
recorded 2026-09-01 · last checked 2026-09-04
Q5
Cetirizine's half-life is 8.3 hours — which schedules were studied?
8.3 hours, the half-life Cetirizine's label states: "Elimination The mean elimination half-life in 146 healthy volunteers across multiple pharmacokinetic studies was 8.3 hours and the apparent total body clearance for cetirizine was approximately 53 mL/min." DailyMed label · 573770f6-b76e-f6ba-e063-6294a90aa54d · 2026-07-31
tmax 0.06 hour.
Show the evidence
half lifepharmacokinetics
8.3 hours; Elimination The mean elimination half-life in 146 healthy volunteers across multiple pharmacokinetic studies was 8.3 hours and the apparent total body clearance for cetirizine was approximately 53 mL/min.
tmaxpharmacokinetics
0.06 hour; Peak concentrations were reached at 0.06 hour (range 0.03 to 0.07 hour) and 0.03 hour (range 0.03 to 2.00 hour) for cetirizine hydrochloride 5 mg and 10 mg IV injection, respectively.
metabolismpharmacokinetics
Metabolism Cetirizine is metabolized to a limited extent by oxidative O-dealkylation to a metabolite with negligible antihistaminic activity.
recorded 2026-07-31 · last checked 2026-09-04
Q6
Which 41 trials of Cetirizine posted no result?
Posted no result
41 of 41 completed trials
Registrations
NCT02932774, NCT00649857, NCT00650065, NCT00639587, NCT00794846 and NCT00794495, and 35 more
Completion dates
oldest 2001-07; newest 2024-03-01
Show the evidence
Trial
NCT02932774
2001-07
NCT00649857
2002-12
NCT00650065
2002-12
NCT00639587
2003-03
NCT00794846
2003-05
NCT00794495
2003-07
14 further recorded trials
NCT00794599
2003-08
NCT00794378
2004-11
NCT00794794
2004-11
NCT00776139
2004-12
NCT00751218
2005-05-24
NCT00776022
2005-06
NCT00504933
2005-11
NCT01064102
2006-02
NCT01064115
2006-02
NCT00334698
2006-09
NCT00863902
2006-09
NCT00864279
2006-09
NCT01127620
2006-11
NCT00420082
2006-12
Q7
At the median, Cetirizine's trials enrolled 51 people — anything larger?
Median enrolment
51
Largest enrolment
3507
Registered trials counted
75
Q8
What do 19546 spontaneous reports say about Cetirizine — 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.
Cetirizine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 19546 reaction mentions were counted: pain 2291; abdominal discomfort 2133; alopecia 2108; systemic lupus erythematosus 2089. FAERS via Open Targets · CHEMBL1000 · 2026-06-24
Show the evidence
pain
2291
abdominal discomfort
2133
alopecia
2108
systemic lupus erythematosus
2089
pemphigus
2084
fatigue
1996
4 more recorded rows
rheumatoid arthritis
1892
glossodynia
1808
swelling
1655
hand deformity
1490
recorded 2026-06-24 · last checked 2026-09-04
Q9
Which 10 reactions does Cetirizine's label not list?
2 label terms; 10 reported and unlisted; 573770f6-b76e-f6ba-e063-6294a90aa54d
Show the evidence
abdominal discomfort
count not stated
alopecia
count not stated
fatigue
count not stated
glossodynia
count not stated
hand deformity
count not stated
pain
count not stated
4 more recorded rows
pemphigus
count not stated
rheumatoid arthritis
count not stated
swelling
count not stated
systemic lupus erythematosus
count not stated
recorded 2026-06-24 · last checked 2026-09-04
Where it is registered
Where it’s registered
Withdrawn in United States, 2026, for "Cross Contamination with Other Products: Customer complaints for appearance of discolored tablets and red dots observed on Cetirizine Hydrochloride Tablets USP 5 mg. Determined to be Ranitidine." (openFDA drug enforcement Class I recall)
ChEMBL 37 — CC BY-SA 3.0 Unported · ChEMBL ATC CC BY-SA · 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 · openFDA enforcement — 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: 7 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.