This page shows what was measured, who it was measured in, and what that does not settle.
What Hydroxyzine does in the body
Hydroxyzine blocks the receptor histamine uses.
In the skin that stops the itch and the hive. In the brain, where histamine is one of the signals keeping you alert, blocking it makes you drowsy and takes the edge off anxiety — which is why one old antihistamine is prescribed for three unrelated-sounding things. The body slowly converts it into cetirizine, a molecule that cannot get into the brain, so the calming effect fades as the conversion proceeds while the anti-itch effect carries on.
Why people take it. Itching from allergy or hives, anxiety, and sedation before an anaesthetic
What happened in people
Response in generalised anxiety disorder against placebo at OR 0.30 (95% CI 0.15 to 0.58) across 5 trials and 884 participants
✎ 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.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
That it keeps working for anxiety beyond four months, which its own label states has never been assessed
Where it acts
H1 receptors in the skin and in the brain. It is the parent compound of cetirizine, which is what the body makes of it and which stays largely out of the brain.
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
13 registered substances share the start of this name, which is why a search for it can return more than one thing.
FDA substance registry · KH6GW2NG3R · read 2026-08-29
Where each sentence above came from
A person wrote this explanation into the record, with the studies named in the path below.
The recorded use, written for a reader without medical training. Not signed off.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 117 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.
Treatment response in generalised anxiety disorder, hydroxyzine against placebo and against other anxiolytics
✓ The study showed what it set out to show
Who was studied
Cochrane hydroxyzine for generalised anxiety disorder (CD006815.pub2)
How many people
884
Study design
Systematic review and meta-analysis of 5 randomised trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Against placebo OR 0.30 (95% CI 0.15 to 0.58); against chlordiazepoxide OR 0.75 (0.35 to 1.62); against buspirone OR 0.76 (0.40 to 1.42); sleepiness against active comparators OR 1.74 (0.86 to 3.53)
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. High risk of bias in all included studies, only 5 of 39 screened studies included, and the included studies did not report all the outcomes prespecified in the review protocol. The reviewers concluded it is not possible to recommend hydroxyzine as a reliable first-line treatment.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablets at 10, 25 and 50 mg of the hydrochloride, an oral syrup, pamoate capsules, and an intramuscular injection for premedication
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
Both actives better than placebo through weeks 1 to 3 and at endpoint (p<0.04) and at week 4 (p<0.001); cetirizine separated from placebo on day 1 (p=0.002) and hydroxyzine on day 2 (p=0.001); the two were judged equivalent
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. Four patients withdrew from the hydroxyzine arm for sedation against one on cetirizine and one on placebo. Nobody withdrew for lack of efficacy in any arm.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablets at 10, 25 and 50 mg of the hydrochloride, an oral syrup, pamoate capsules, and an intramuscular injection for premedication
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
Incident dementia by cumulative 10-year strong anticholinergic exposure in adults 65 and over
✓ The study showed what it set out to show
Who was studied
Adult Changes in Thought anticholinergic cohort (JAMA Intern Med 2015;175:401-407)
How many people
3434
Study design
Prospective population-based cohort, class-level exposure, mean 7.3 years
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Adjusted HR 1.54 (95% CI 1.21 to 1.96) above 1,095 total standardised daily doses, with a dose-response trend at p<0.001
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. This is class-level evidence for first-generation antihistamines, not a hydroxyzine-specific result, and the cohort is observational. It is included because hydroxyzine is classified as a strong anticholinergic in the scales that study and the Beers Criteria use.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablets at 10, 25 and 50 mg of the hydrochloride, an oral syrup, pamoate capsules, and an intramuscular injection for premedication
Interval reported. 95% CI 1
Written into the record, not signed off as a reviewed claim.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
RNAWiki holds 3 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.
Where a source records it acting
Brain: Not a cortical depressant; action may be due to a suppression of activity in certain key regions of the subcortical area of the central nervous system
US prescribing information · 02616eee-a1a4-4afc-b84e-69fd28755138 · read 2026-08-27
Start
Hydroxyzine
What a person takes: Oral tablets at 10, 25 and 50 mg of the hydrochloride, an oral syrup, pamoate capsules, and an intramuscular injection for premedication.
The measurement behind this step
Rapidly absorbed with clinical effects usually noted within 15 to 30 minutes after an oral dose. The label states that when treatment is initiated intramuscularly, subsequent doses may be given orally. It potentiates central nervous system depressants including narcotics, non-narcotic analgesics and barbiturates, and the label directs in capitals that their doses be reduced when given together.
Getting in
Absorbed fast, felt within half an hour
A tablet or capsule that works quickly — the label puts clinical effects at 15 to 30 minutes after swallowing.
╌╌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
Rapidly absorbed from the gastrointestinal tract, with clinical effects usually noted within 15 to 30 minutes of oral administration. Supplied as the dihydrochloride in tablets and syrup and as the pamoate in capsules. The label states hydroxyzine is chemically unrelated to the phenothiazines, reserpine, meprobamate or the benzodiazepines.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
It crosses into the brain, unlike its own metabolite
The terminal alcohol on the molecule keeps it fat-soluble enough to enter the brain. Oxidise it to an acid and you get cetirizine, which cannot.
╌╌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
A diphenylmethylpiperazine with a hydroxyethoxyethyl arm. Oxidation of that primary alcohol to a carboxylic acid gives cetirizine, zwitterionic at physiological pH and largely excluded from the central nervous system. One functional group is the difference between a sedative and a non-sedating allergy tablet.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
It blocks the histamine receptor in skin and brain alike
In the skin that is the anti-itch effect. In the brain it is the drowsiness, and it is most of what the anxiolytic effect consists of.
╌╌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
Competitive H1 antagonism. The label does not name the receptor in its account of the anxiolytic action, saying instead that hydroxyzine is not a cortical depressant but that its action may be due to a suppression of activity in certain key regions of the subcortical area of the central nervous system.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
That is the dry mouth, and it is why this class is on the list of medicines to avoid in older people.
╌╌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
Muscarinic antagonism sufficient for classification as a strong anticholinergic in the scales used by the Beers Criteria and the cumulative-exposure cohort literature. The label lists dry mouth as the anticholinergic adverse reaction and notes potentiation of central nervous system depressants including narcotics, non-narcotic analgesics and barbiturates.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
For hives it works about as well as its metabolite. For anxiety it beats a dummy tablet and roughly matches a benzodiazepine, on a small and shaky evidence base.
──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
Chronic idiopathic urticaria: hydroxyzine 25 mg three times daily equivalent to cetirizine 10 mg once daily over 4 weeks in 188 patients. Generalised anxiety: OR 0.30 (95% CI 0.15 to 0.58) against placebo across 5 trials and 884 participants, equivalent to chlordiazepoxide and buspirone, at high risk of bias.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · a recorded source, not a stored snapshot
It lengthens the electrical recovery of the heart, it makes people drowsy more than the alternatives do, and past four months nobody has tested whether it still works.
──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
Contraindicated in prolonged QT interval; postmarketing QT prolongation and torsade de pointes, mostly in patients with other risk factors. Sleepiness and drowsiness at OR 1.74 (95% CI 0.86 to 3.53) against active comparators. Effectiveness as an antianxiety agent beyond 4 months not assessed by systematic clinical studies, per the label.
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · 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 chronic itch and hives, people with anxiety who are being kept away from benzodiazepines, and patients being premedicated for anaesthesia.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
Where the result stopped carrying
The Cochrane reviewers declined to recommend it as a reliable first-line anxiolytic despite a positive result against placebo, on grounds of bias and evidence volume
The European regulator restricted maximum daily dose fourfold below the United States figure and made several risk factors outright contraindications
Acute generalised exanthematous pustulosis was recognised only in postmarketing reports, and required a cross-sensitivity instruction covering two other marketed drugs
Contraindicated in early pregnancy on animal teratogenicity with human data the label calls inadequate
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
Given by a clinician
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral tablets at 10, 25 and 50 mg of the hydrochloride, an oral syrup, pamoate capsules, and an intramuscular injection for premedication
✎ 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 clinical effects usually noted within 15 to 30 minutes after an oral dose. The label states that when treatment is initiated intramuscularly, subsequent doses may be given orally. It potentiates central nervous system depressants including narcotics, non-narcotic analgesics and barbiturates, and the label directs in capitals that their doses be reduced when given together.
✎ 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
Contraindicated in prolonged QT interval, in known hypersensitivity to hydroxyzine, cetirizine or levocetirizine, and in early pregnancy — the last on fetal abnormalities in rat and mouse at doses substantially above the human range, with human data the label describes as inadequate. QT prolongation and torsade de pointes reported postmarketing, mostly in patients with pre-existing heart disease, electrolyte imbalance or other arrhythmogenic drugs, with an extensive list of interacting classes. Acute generalised exanthematous pustulosis and fixed drug eruptions, with an instruction to avoid cetirizine and levocetirizine afterwards. Drowsiness, with warnings against driving and against alcohol. Dry mouth as the anticholinergic effect. Involuntary motor activity including rare tremor and convulsions, usually at doses considerably above those recommended. Hallucination and headache reported postmarketing. Not to be given to nursing mothers.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Where this came from
Hydroxyzine hydrochloride United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Contraindications, Warnings, Pre… · a recorded source, not a stored snapshot
European Medicines Agency. New restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines — Article 31 referral outc… · 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 tablets at 10, 25 and 50 mg of the hydrochloride, an oral syrup, pamoate capsules, and an intramuscular injection for premedication
✎ 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
The label states that when treatment is initiated intramuscularly, subsequent doses may be given orally. It potentiates central nervous system depressants including narcotics, non-narcotic analgesics and barbiturates, and the label directs in capitals that their doses be reduced when given together.
✎ 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
122 products list this as an active ingredient in the United States drug directory. 122 of them contain it and nothing else.
FDA National Drug Code directory · 87441-040 · read 2026-08-29
They are sold as capsule, powder, solution, tablet and tablet, film coated, taken oral.
FDA National Drug Code directory · 87441-040 · read 2026-08-29
The regulator's established pharmacologic class for it is antihistamine [epc] and histamine receptor antagonists [moa].
FDA National Drug Code directory · 87441-040 · read 2026-08-29
221 published labels name it as an active ingredient. 221 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 1a3e389f-391d-4f37-9e34-ce3c6f5fe8c1 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 1a3e389f-391d-4f37-9e34-ce3c6f5fe8c1 · read 2026-08-29
hydroxyzine pamoate is capsules at 25 mg (equivalent to 25 mg hydroxyzine hydrochloride), recorded as prescription product; fda label in effect 2024-12-16 in the United States.
US prescribing information · 02616eee-a1a4-4afc-b84e-69fd28755138 · read 2026-08-27
Recorded price in US: 0.02856–0.05831 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 65 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: 0.10891 USD per one millilitre, across 7 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 Hydroxyzine 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 it keeps working for anxiety beyond four months, which its own label states has never been assessed
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 not being a controlled substance implies it is a safe long-term choice, when the specific harms it does carry are cardiac and anticholinergic rather than dependence
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 label’s clinically confirmed bronchodilator and analgesic effects are real therapeutic properties, when neither is an indication and neither has modern support
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 anxiolytic action is subcortical suppression, a 1956 formulation that names no receptor and has not been updated
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 Hydroxyzine 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.
Two regulators, one drug, a fourfold difference in maximum daily dose
In plain words
Europe reviewed the heart-rhythm risk in 2015 and capped hydroxyzine at 100 mg a day for adults and 50 mg for older people. The United States label still prints an anxiety dose of 50 to 100 mg four times a day.
What was measured
Maximum daily dose and contraindication set in the European and United States labelling for the same molecule
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Following an Article 31 referral, the European Medicines Agency concluded in 2015 that hydroxyzine carries a small but definite risk of QT interval prolongation and torsade de pointes, and imposed a set of restrictions: use at the lowest effective dose for the shortest possible duration, a maximum of 100 mg daily in adults, 50 mg daily in the elderly if use cannot be avoided, and 2 mg/kg/day in children up to 40 kg. It contraindicated use in known acquired or congenital QT prolongation and in patients with a known risk factor including cardiovascular disease, significant electrolyte imbalance, family history of sudden cardiac death, significant bradycardia or concomitant QT-prolonging drugs, and stated that use is not recommended in elderly patients. The United States label contraindicates hydroxyzine in patients with a prolonged QT interval and carries a detailed QT precaution listing interacting drug classes — but its Dosage and Administration section still reads, for anxiety in adults, 50 to 100 mg four times daily. Nothing here is a dosing instruction to any reader; the point is that two regulators looking at the same molecule and the same safety data ended four years apart at maximum daily doses that differ by a factor of four, and the older document is the one that was never revised.
Source
European Medicines Agency, new restrictions to minimise the risks of effects on heart rhythm with hydroxyzine-containing medicines (Article 31 referral, 2015); hydroxyzine hydrochloride United States prescribing information, Contraindications, Precautions and Dosage and Administration
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 beats placebo for anxiety on evidence its own reviewers would not rely on
In plain words
Five randomised trials in 884 people found hydroxyzine better than a dummy tablet for generalised anxiety, and about as good as a benzodiazepine or buspirone. The reviewers still refused to call it a reliable first-line treatment, because the trials were poorly conducted and there were not many of them.
What was measured
Treatment response in generalised anxiety disorder, hydroxyzine against placebo and against benzodiazepine and buspirone comparators
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Cochrane review of hydroxyzine for generalised anxiety disorder screened 39 studies and included 5, with 884 participants. Against placebo the odds ratio for response was 0.30 (95% CI 0.15 to 0.58) in the review’s direction of effect, with acceptability and tolerability not differing from placebo (OR 1.00, 95% CI 0.63 to 1.58; OR 1.49, 95% CI 0.92 to 2.40). Against other anxiolytics hydroxyzine was equivalent: against chlordiazepoxide OR 0.75 (95% CI 0.35 to 1.62), against buspirone OR 0.76 (95% CI 0.40 to 1.42). It caused more sleepiness and drowsiness than the active comparators, OR 1.74 (95% CI 0.86 to 3.53). The reviewers recorded a high risk of bias in the included studies, noted that the studies did not report all the prespecified outcomes, and concluded that despite being more effective than placebo it is not possible to recommend hydroxyzine as a reliable first-line treatment in generalised anxiety disorder. That is a positive result and a negative recommendation in the same paragraph, and both are correct.
Written into the record, not signed off as a reviewed claim
Beyond four months, the label says nobody has looked
In plain words
Hydroxyzine is frequently prescribed for anxiety month after month. Its own prescribing information states that its effectiveness for use beyond four months has never been assessed in systematic clinical studies.
What was measured
Duration of use for which systematic effectiveness data exist, as stated in the label
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Indications and Usage section states, in full: "The effectiveness of hydroxyzine as an antianxiety agent for long term use, that is more than 4 months, has not been assessed by systematic clinical studies. The physician should reassess periodically the usefulness of the drug for the individual patient." The Cochrane evidence base is consistent with that: the included trials were short, and the review reported nothing about durability. This matters more than it would for most drugs because of why hydroxyzine is chosen. It is prescribed for anxiety largely because it is not a controlled substance and does not cause the dependence benzodiazepines do — a comparison about a harm. Nothing about the absence of that harm implies the benefit persists, and the label is unusually candid that the question was never asked.
Source
Hydroxyzine hydrochloride United States prescribing information, Indications and Usage
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
A mechanism paragraph that names no receptor, and three claims from 1956
In plain words
The label explains how the drug calms anxiety by saying it is not a cortical depressant and that its action may be due to suppressing activity in certain key regions of the subcortical brain. It also states that bronchodilator, analgesic and muscle-relaxant effects have been demonstrated and clinically confirmed.
What was measured
That hydroxyzine has clinically confirmed bronchodilator and analgesic activity, and that its anxiolytic effect is explained by subcortical suppression — claims printed in the label with no receptor, no trial and no modern support
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Clinical Pharmacology section reads: hydroxyzine is unrelated chemically to the phenothiazines, reserpine, meprobamate or the benzodiazepines; it is not a cortical depressant, but its action may be due to a suppression of activity in certain key regions of the subcortical area of the central nervous system; primary skeletal muscle relaxation has been demonstrated experimentally; bronchodilator activity, and antihistaminic and analgesic effects have been demonstrated experimentally and confirmed clinically; an antiemetic effect has been demonstrated by the apomorphine test and the veriloid test. The histamine H1 receptor is not named anywhere in that paragraph, and the modern understanding — that the anxiolytic and sedative effects are central H1 antagonism, with a contribution from 5-HT2A antagonism — is absent. The bronchodilator and analgesic claims would not survive a contemporary efficacy review and are not indications, yet they sit in the document a prescriber reads. This is what an unrevised 1956 pharmacology section looks like when there is no innovator sponsor and no regulatory trigger to rewrite it.
Source
Hydroxyzine hydrochloride United States prescribing information, Clinical Pharmacology
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
Its own metabolite matched it for hives, once a day, with less sedation
In plain words
Cetirizine is what the body turns hydroxyzine into. Given once daily it controlled chronic hives as well as hydroxyzine given three times a day, and four times fewer people dropped out because of drowsiness.
What was measured
Urticaria episode count, lesion number and size, pruritus severity and sedation withdrawals over 4 weeks
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A 4-week multicentre randomised double-blind double-dummy placebo-controlled trial in 188 patients aged 12 and over with chronic idiopathic urticaria compared cetirizine 10 mg once daily, hydroxyzine 25 mg three times daily and placebo. Cetirizine separated from placebo on episode count and pruritus after one day (p=0.002); hydroxyzine did not reach significance until day 2 (p=0.001). Both actives reduced lesion number and size and pruritus severity against placebo through weeks 1, 2 and 3 and at endpoint (p<0.04), and both were rated improved against placebo at week 4 (p<0.001). Four patients on hydroxyzine discontinued for sedation, against one on cetirizine and one on placebo; nobody withdrew for lack of efficacy. The authors concluded cetirizine 10 mg once daily was equivalent to hydroxyzine 25 mg three times daily. For the itch indication this is close to a complete answer: the metabolite does the job on a third of the dosing occasions with less of the cost, and the only thing the parent adds is the central effect.
Written into the record, not signed off as a reviewed claim
The parent and its metabolite are now treated as a single allergen
In plain words
A severe pustular rash was recognised in postmarketing reports. The label now directs that anyone who has had it with hydroxyzine must also avoid cetirizine and levocetirizine, because they are the same molecule after metabolism.
What was measured
Cross-sensitivity instruction linking hydroxyzine, cetirizine and levocetirizine in the current labelling
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The label records that hydroxyzine may rarely cause acute generalised exanthematous pustulosis, described as a serious skin reaction with fever and numerous small superficial non-follicular sterile pustules arising within large areas of oedematous erythema, and directs discontinuation at the first appearance of a rash, at any worsening of a pre-existing skin reaction the drug is being used to treat, or at any other sign of hypersensitivity. If AGEP is suspected the label states hydroxyzine should not be resumed. It then goes further and instructs avoiding cetirizine or levocetirizine in anyone who has had AGEP or another hypersensitivity reaction with hydroxyzine, because of cross-sensitivity — and the Contraindications section runs the rule the other way, contraindicating hydroxyzine in patients with known hypersensitivity to cetirizine or levocetirizine. Three separately marketed products, two of them approved decades apart as distinct entities, are handled by the labelling as one immunological object. The warning that a drug being used to treat a rash may be causing it is the part clinicians most often miss.
Source
Hydroxyzine hydrochloride United States prescribing information, Contraindications, Precautions — Acute Generalized Exanthematous Pustulosis, and Adverse Reactions
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
Where else this substance is registered
CAS registry number
68-88-8
PubChem compound
3658
RxNorm concept
154987
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What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
What the approval register records
146 approved applications cover products containing this substance. The earliest was NDA010392, approved 19560412 to PFIZER.
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What is not here
7 questions this page could not answer
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Felt, measured, or meaningful — found nothing in the sources checked.
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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 first-generation antihistamine that beat placebo for generalised anxiety at an odds ratio of 0.30 across five trials and 884 patients — on evidence the reviewers judged at high risk of bias and insufficient to make it a reliable first-line treatment — which is contraindicated in prolonged QT interval, carries a United States maximum daily dose four times the European cap imposed in 2015 for that same cardiac risk, and whose own label admits its effectiveness beyond four months has never been studied.
Recorded evidence blocks (8)
Q1
On the Hydroxyzine label: indicated for what?
"INDICATIONS For symptomatic relief of anxiety and tension associated with psychoneurosis and as an adjunct in organic disease states in which anxiety is manifested. Useful in the management of pruritus due to allergic conditions such as chronic urticaria and atopic and contact dermatoses, and in histamine-mediated…": indications and usage on Hydroxyzine's label. DailyMed label · 0c9101ee-0746-4833-83cf-d0d09e52c0a9 · 2026-08-05
Q2
19 registered trials of Hydroxyzine — at which phases?
"Due to unforseen recruiting difficulties, the study was closed."; 2 of 19 registered studies
Show the evidence
Trial
NCT01372670
withdrawn; "Due to unforseen recruiting difficulties, the study was closed."
NCT03324828
terminated; "COVID-19"
recorded 2026-09-01 · last checked 2026-09-04
Q4
Human studies of Hydroxyzine used ATARAX 200 ml syrup,8699624570062,N05BB01 — over how long?
Human studies of Hydroxyzine used "ATARAX 200 ml syrup,8699624570062,N05BB01". ClinicalTrials.gov · 2026-09-01
3 recorded entries; human; also "Hydroxyzine 25mg", "Atarax 10mg"
Show the evidence
human
NCT03806270
ATARAX 200 ml syrup,8699624570062,N05BB01
NCT03808805
Hydroxyzine 25mg
NCT05680584
Atarax 10mg
recorded 2026-09-01 · last checked 2026-09-04
Q5
Which 5 trials of Hydroxyzine posted no result?
Posted no result
5 of 5 completed trials
Registrations
NCT01055236, NCT01496911, NCT01151696, NCT05492812 and NCT03808805
Completion dates
oldest 2008-10; newest 2024-08-22
Show the evidence
Trial
NCT01055236
2008-10
NCT01496911
2012-10
NCT01151696
2014-01
NCT05492812
2021-12-31
NCT03808805
2024-08-22
Q6
At the median, Hydroxyzine's trials enrolled 80 people — anything larger?
Median enrolment
80
Largest enrolment
407
Registered trials counted
19
Q7
What do 344 spontaneous reports say about Hydroxyzine — 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.
Hydroxyzine appears in spontaneous reports to regulators. Across the 6 most-reported reaction terms, 344 reaction mentions were counted: drug hypersensitivity 300; somnolence 20; convulsion 12; neurotoxicity 7. FAERS via Open Targets · CHEMBL1200467 · 2026-06-24
Show the evidence
drug hypersensitivity
300
somnolence
20
convulsion
12
neurotoxicity
7
nuclear magnetic resonance imaging brain abnormal
3
false positive laboratory result
2
recorded 2026-06-24 · last checked 2026-09-04
Q8
Which 6 reactions does Hydroxyzine's label not list?
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
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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.