This page shows what was measured, who it was measured in, and what that does not settle.
What CHLORPHENIRAMINE, (-)- does in the body
Sneezing, runny nose and itchy eyes — the old allergy tablet
Chlorpheniramine sits in the receptor histamine uses, so histamine arrives and finds nowhere to dock. That stops the sneeze, the runny nose and the itch. Unlike the newer allergy tablets it also crosses freely into the brain, where histamine is one of the signals that keeps you awake, so it blocks that too. And it blocks a second, unrelated receptor — the one acetylcholine uses — which is why it dries you out, and why it blurs vision, holds up urine and clouds thinking in people who are susceptible.
What happened in people
Cortical H1 receptor occupancy of 53.0 ± 33.2% at a standard dose, against 11.7 ± 19.5% for loratadine 10 mg
✎ 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.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
The limit that matters most
That the anticholinergic drying is a therapeutic feature, when it is absent from the newer antihistamines that treat the same symptoms
Where it acts
H1 receptors on blood vessels and sensory nerves in the nose and eyes — and, unlike the newer antihistamines, H1 receptors throughout the cerebral cortex
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
15 registered substances share the start of this name, which is why a search for it can return more than one thing.
FDA substance registry · 5T8587JTSU · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 121 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.
Cortical histamine H1 receptor occupancy after single oral doses of d-chlorpheniramine 2 mg and loratadine 10 mg in patients with allergic rhinitis
✓ The study showed what it set out to show
Who was studied
Carbon-11 doxepin PET receptor occupancy crossover (Hum Psychopharmacol 2011;26:133-139)
How many people
11
Study design
Double-blind, randomised crossover imaging study
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
d-Chlorpheniramine 53.0 ± 33.2% against loratadine 11.7 ± 19.5%; occupancy proportional to the published proportional impairment ratio across drugs, r=0.899
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. Eleven young male participants is a small and narrow sample, and the standard deviations are very wide — 33 points around a 53-point mean. The direction of the difference is unambiguous; the precision of either figure is not.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral: 4 mg immediate-release tablets, extended-release tablets, syrups and oral solutions, and a very large number of fixed-dose combination cold and flu products
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
US Food and Drug Administration. Use Caution When Giving Cough and Cold Products to Kids — consumer safety guidance on antihistamine- and decongestant-contai… · a recorded source, not a stored snapshot
Severity of overall cold symptoms, antihistamine 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 or six to ten days; rhinorrhoea day three MD -0.23 (-0.39 to -0.06), sneezing day three -0.35 (-0.49 to -0.20), both judged clinically non-significant
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. Only two of the 18 trials included children and the results conflicted; the reviewers concluded there is no evidence of effectiveness in children. That is the same population in which the products were withdrawn on safety grounds.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral: 4 mg immediate-release tablets, extended-release tablets, syrups and oral solutions, and a very large number of fixed-dose combination cold and flu products
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
US Food and Drug Administration. Use Caution When Giving Cough and Cold Products to Kids — consumer safety guidance on antihistamine- and decongestant-contai… · a recorded source, not a stored snapshot
Incident dementia and Alzheimer disease by cumulative 10-year 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, mean 7.3 years follow-up
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Adjusted HR 0.92 (95% CI 0.74 to 1.16), 1.19 (0.94 to 1.51), 1.23 (0.94 to 1.62) and 1.54 (1.21 to 1.96) across rising exposure bands; test for trend p<0.001; 797 of 3,434 (23.2%) developed dementia
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. Observational. The most recent 12 months of exposure were excluded to reduce reverse causation from prodromal symptoms, and results were reported as robust in sensitivity analyses, but confounding by indication cannot be excluded for a class taken for insomnia, allergy and bladder symptoms that all track with age.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral: 4 mg immediate-release tablets, extended-release tablets, syrups and oral solutions, and a very large number of fixed-dose combination cold and flu products
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
US Food and Drug Administration. Use Caution When Giving Cough and Cold Products to Kids — consumer safety guidance on antihistamine- and decongestant-contai… · a recorded source, not a stored snapshot
What we know
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.
Start
CHLORPHENIRAMINE, (-)-
What a person takes: Oral: 4 mg immediate-release tablets, extended-release tablets, syrups and oral solutions, and a very large number of fixed-dose combination cold and flu products.
The measurement behind this step
The over-the-counter directions for the plain tablet are one every four to six hours in adults and children 12 and over, to a maximum of 24 mg in 24 hours, with children under 12 directed to consult a doctor. Onset is fast because the molecule is small and lipophilic — the same property that gives it its brain exposure. It is also available as the single-enantiomer dexchlorpheniramine at half the milligram strength.
Getting in
A small, greasy molecule that goes everywhere
Swallowed as a tablet, absorbed quickly, and — unlike the newer allergy tablets — free to cross into the brain.
╌╌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 propylamine antihistamine with a tertiary amine, a chlorophenyl ring and a pyridine ring: small, lipophilic, and lacking the ionisable carboxylate or efflux-transporter substrate character that keeps second-generation agents peripheral. Dispensed as the maleate salt, dosed every four to six hours.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
What it acts on
It occupies the histamine receptor in the nose
Histamine released by allergy cells finds the receptor already taken, so the vessels do not leak and the nerves do not fire.
╌╌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 receptor antagonism on vascular endothelium and sensory nerve endings in the nasal and conjunctival mucosa. The monograph indication reflects exactly what that blocks: sneezing, runny nose, itching of the nose or throat, and itchy watery eyes — not congestion.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
Reaching the cell
It occupies the same receptor in the brain
Histamine is one of the brain’s wakefulness signals. Blocking it there is what makes you drowsy, and the amount blocked has been measured.
╌╌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
Cortical H1 receptor occupancy of 53.0 ± 33.2% at the d-chlorpheniramine 2 mg equivalent of a standard tablet, by carbon-11 doxepin PET, against 11.7 ± 19.5% for loratadine 10 mg. Occupancy across drugs correlated with the proportional impairment ratio at r=0.899.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
The change it makes
And it blocks a second, different receptor entirely
The acetylcholine receptor. That is the drying — of the nose, and of the mouth, eyes, gut and bladder along with it.
──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
Muscarinic antagonism sufficient to classify chlorpheniramine as a strong anticholinergic in the scales used by the Beers Criteria and by the Adult Changes in Thought cohort. The Drug Facts warnings for glaucoma, prostatic obstruction and chronic airway disease are anticholinergic warnings.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
What that does for a person
Symptoms settle for a few hours
Fast and effective for the sneeze, the drip and the itch, and gone again in four to six hours.
──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
The over-the-counter directions are one 4 mg tablet every four to six hours to a maximum of 24 mg in 24 hours in adults and children 12 and over, with children under 12 directed to consult a doctor. Nothing in the monograph indication addresses nasal blockage or asthma.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · a recorded source, not a stored snapshot
What that does for a person
And the exposure accumulates over a lifetime
Each dose is trivial. The measure that matters in the cohort data is ten years of cumulative anticholinergic exposure, and at the top of that range dementia was half again as common.
──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
Adjusted hazard ratio 1.54 (95% CI 1.21 to 1.96) for incident dementia at more than 1,095 total standardised daily doses over 10 years, with a dose-response trend at p<0.001, in 3,434 adults aged 65 and over. First-generation antihistamines were one of the three commonest exposure classes.
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · 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.
Anyone who buys allergy tablets or a multi-symptom cold remedy. It is in an enormous number of combination products, which is the main route to accidental double-dosing.
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 paediatric use case: infant products withdrawn, remaining products relabelled to exclude children under 4
The common cold indication: a two-day benefit on a global score and clinically non-significant effects on individual symptoms
The older-adult use case: first-generation antihistamines are on the Beers list of medicines typically best avoided over 65
The regulatory record: no modern efficacy package exists and no party is obliged to produce one
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: 4 mg immediate-release tablets, extended-release tablets, syrups and oral solutions, and a very large number of fixed-dose combination cold and flu products
✎ 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
The over-the-counter directions for the plain tablet are one every four to six hours in adults and children 12 and over, to a maximum of 24 mg in 24 hours, with children under 12 directed to consult a doctor.
✎ 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: Onset is fast because the molecule is small and lipophilic — the same property that gives it its brain exposure. It is also available as the single-enantiomer dexchlorpheniramine at half the milligram strength.
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 at ordinary doses, with the carton directing caution when driving or operating machinery and avoidance of alcohol, sedatives and tranquillisers. Paradoxical excitability, especially in children. Anticholinergic effects — dry mouth, blurred vision, constipation, urinary retention, confusion — with the carton directing that anyone with glaucoma, prostatic enlargement or chronic airway disease ask a doctor first. Contraindicated with monoamine oxidase inhibitors in the combination products that carry them. Not to be given to children under 2 in any cough and cold product containing an antihistamine or decongestant, and the remaining products are labelled do not use under 4 years. Listed by the American Geriatrics Society among medicines typically best avoided in adults 65 and over.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Where this came from
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 — Uses, Warnings, When using this product, Ask a doctor before use, Direc… · a recorded source, not a stored snapshot
Centers for Disease Control and Prevention. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1)… · 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: 4 mg immediate-release tablets, extended-release tablets, syrups and oral solutions, and a very large number of fixed-dose combination cold and flu products
✎ 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
Onset is fast because the molecule is small and lipophilic — the same property that gives it its brain exposure. It is also available as the single-enantiomer dexchlorpheniramine at half the milligram strength.
✎ 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
307 products list this as an active ingredient in the United States drug directory. 49 of them contain it and nothing else.
FDA National Drug Code directory · 0485-0098 · read 2026-08-29
They are sold as aerosol, spray, capsule, capsule, gelatin coated, capsule, liquid filled, concentrate and granule, taken oral and topical.
FDA National Drug Code directory · 0485-0098 · 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 · 0485-0098 · read 2026-08-29
275 published labels name it as an active ingredient. 37 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 1f93fe6d-ee21-e323-e063-6394a90a61bf · read 2026-08-29
Those labels are classed as human otc drug and human prescription drug.
US prescribing information · 1f93fe6d-ee21-e323-e063-6394a90a61bf · read 2026-08-29
Chlorpheniramine Maleate 4 mg is oral at HOW SUPPLIED NDC: 71335-0963-1: 30 Tablets in a BOTTLE NDC: 71335-0963-2: 60 Tablets in a BOTTLE NDC: 71335-0963-3: 100 Tablets in a BOTTLE NDC: 71335-0963-4: 120 Tablets in a BOTTLE NDC: 71335-0963-5: 40 Tablets in a B…, recorded as fda label in effect 2024-05-17 in the United States.
US prescribing information · 54681242-c861-4415-b5c0-d3ab55b62be1 · read 2026-08-30
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
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 CHLORPHENIRAMINE, (-)- studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That the anticholinergic drying is a therapeutic feature, when it is absent from the newer antihistamines that treat the same symptoms
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 drowsiness is an idiosyncratic side effect rather than a direct readout of target engagement in the brain
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 cumulative anticholinergic exposure causes dementia, which the cohort design supports but cannot establish
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That an ingredient grandfathered under a monograph has been shown to work by the standard applied to every drug approved since 1962
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 CHLORPHENIRAMINE, (-)- 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.
Half the histamine receptors in your cortex, measured by brain scan
In plain words
Eleven people with hay fever were scanned after a standard dose. Chlorpheniramine had taken up 53% of the histamine receptors in the cerebral cortex. Loratadine, at its standard dose, had taken up 12%.
What was measured
Cortical histamine H1 receptor occupancy by carbon-11 doxepin PET, and its correlation with the proportional impairment ratio
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A double-blind crossover positron emission tomography study using carbon-11 doxepin measured cortical histamine H1 receptor occupancy in 11 young male patients with allergic rhinitis after single oral doses. d-Chlorpheniramine 2 mg — the quantity of active enantiomer contained in a standard 4 mg racemic chlorpheniramine tablet — occupied 53.0 ± 33.2% of cortical H1 receptors. Loratadine 10 mg occupied 11.7 ± 19.5%. Across this and previous studies, receptor occupancy was significantly proportional to the published proportional impairment ratio, with a correlation coefficient of 0.899. That last number is what makes this an audit rather than a curiosity: it establishes that the drowsiness and slowed reactions are a direct readout of target engagement in the brain, not an idiosyncratic side effect that some people happen to get.
Written into the record, not signed off as a reviewed claim
Withdrawn for infants after deaths, and relabelled for everyone under four
In plain words
Cough and cold products containing antihistamines were given to babies for decades. After three infant deaths in one year were attributed to them by medical examiners, manufacturers pulled the infant products and relabelled the rest.
What was measured
Attributed infant deaths and emergency department presentations, and the labelling age limit before and after 2007
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A CDC and National Association of Medical Examiners investigation identified three deaths of infants under 6 months in 2005 for which cough and cold medications were determined by medical examiners or coroners to be the underlying cause, against a background of an estimated 1,519 children under 2 treated in United States emergency departments for adverse events including overdoses during 2004 to 2005. The report noted that the doses at which these medicines cause illness or death in children under 2 are not known, that FDA-approved dosing recommendations for that age group do not exist, and that published evidence of effectiveness in that age group is limited. After a 2007 FDA meeting, manufacturers voluntarily removed over-the-counter infant cough and cold products and voluntarily relabelled the remaining products to state do not use in children under 4 years of age. FDA’s current consumer guidance states plainly that children under 2 should not be given any cough and cold product containing a decongestant or antihistamine, because serious and possibly life-threatening side effects could occur, including convulsions, rapid heart rates and death.
Source
CDC. Infant deaths associated with cough and cold medications — two states, 2005. MMWR Morb Mortal Wkly Rep 2007;56(1):1-4; FDA, Use Caution When Giving Cough and Cold Products to Kids
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
The cold products it lives in do almost nothing for a cold
In plain words
Antihistamines in colds were tested in eighteen randomised trials. There was a small benefit on days one and two and nothing after that, and the effects on runny nose and sneezing were judged too small to matter.
What was measured
Overall cold symptom severity and individual symptom scores by day, antihistamine against placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Cochrane review of antihistamine monotherapy for the common cold included 18 randomised trials in 4,342 participants, excluding anyone with an allergic component to their illness. 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 six to ten days. Sedating antihistamines specifically did produce measurable effects on individual symptoms — rhinorrhoea on day three, mean difference -0.23 (95% CI -0.39 to -0.06) on a four- or five-point scale, and sneezing on day three, -0.35 (95% CI -0.49 to -0.20) on a four-point scale — which the reviewers described as clinically non-significant. Adverse effects including sedation were more commonly reported with the sedating agents, though the difference was not statistically significant. Only two trials included children, with conflicting results, and the reviewers concluded there is no evidence of effectiveness in children. Chlorpheniramine’s largest commercial presence in the United States is precisely as one ingredient among several in multi-symptom cold and flu products.
Written into the record, not signed off as a reviewed claim
A cumulative dementia signal for the class, tracked over ten years
In plain words
Three and a half thousand people over sixty-five were followed for years. Those with the heaviest ten-year exposure to strongly anticholinergic drugs — of which first-generation antihistamines are one of the three biggest sources — developed dementia about half again as often.
What was measured
That cumulative anticholinergic exposure causes dementia, rather than marking populations at higher risk for other reasons — an inference the dose-response gradient supports and an observational design cannot establish
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Adult Changes in Thought prospective cohort followed 3,434 participants aged 65 and over with no dementia at entry, using dispensing records to compute cumulative anticholinergic exposure as total standardised daily doses over the preceding 10 years, excluding the most recent 12 months to avoid prodromal reverse causation. The most common anticholinergic classes used were tricyclic antidepressants, first-generation antihistamines and bladder antimuscarinics. Over a mean 7.3 years, 797 participants (23.2%) developed dementia. Adjusted hazard ratios against non-use were 0.92 (95% CI 0.74 to 1.16) at 1 to 90 total standardised daily doses, 1.19 (0.94 to 1.51) at 91 to 365, 1.23 (0.94 to 1.62) at 366 to 1,095 and 1.54 (1.21 to 1.96) above 1,095, with a dose-response trend at p<0.001. This is an observational cohort and it cannot establish causation, but the dose-response gradient and the exclusion of the final year are the two design features that most weaken the obvious alternative explanations. The American Geriatrics Society Beers Criteria list first-generation antihistamines among the medicines typically best avoided in adults 65 and over.
Written into the record, not signed off as a reviewed claim
The drying effect and the harm list are the same pharmacology
In plain words
People value this drug because it dries you up. The carton’s own list of who should ask a doctor first — glaucoma, prostate trouble, chronic lung disease — is the standard warning list for exactly that drying mechanism.
What was measured
That the anticholinergic drying is a therapeutic property worth having, when it is separable from H1 blockade, absent from the newer agents, and the source of the class’s characteristic harms
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Chlorpheniramine is a muscarinic acetylcholine receptor antagonist as well as an H1 antagonist. The over-the-counter Drug Facts direct the reader to ask a doctor before use if they have a breathing problem such as emphysema or chronic bronchitis, glaucoma, or difficulty in urination due to enlargement of the prostate gland. Those three conditions are the textbook contraindications to anticholinergic drugs: thickened secretions in chronic airway disease, angle closure in predisposed eyes, and worsened bladder outlet obstruction. The secretion-drying that makes the molecule useful in a cold remedy, the urinary retention, the blurred vision, the constipation and the confusion in older patients are one mechanism described four ways. The second-generation antihistamines block the same histamine receptor with negligible muscarinic activity, which means the drying is separable from the antihistamine effect and is not part of what makes an allergy tablet work.
Source
Chlorpheniramine maleate over-the-counter Drug Facts labelling under monograph M012 (openFDA SPL); receptor pharmacology as reflected in the anticholinergic classification used by the Beers Criteria and the Adult Changes in Thought cohort
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 has never been through the modern efficacy standard
In plain words
Chlorpheniramine reached the market in 1949, thirteen years before American law began requiring proof that a drug works. It is sold today under a monograph rather than an approval, so there is no trial package behind it and no company obliged to produce one.
What was measured
Regulatory pathway — monograph rather than approved application — and the date of market entry against the date of the effectiveness requirement
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The 1962 Drug Amendments introduced the requirement for substantial evidence of effectiveness. Chlorpheniramine predates it by thirteen years, and today it is marketed in the United States under over-the-counter monograph M012 — the pathway for active ingredients deemed generally recognised as safe and effective on the basis of historical use and expert panel review, not on the basis of an approved application supported by controlled trials. The consequences are structural rather than scandalous. There is no sponsor, so there is no party with a commercial reason to fund the trials that would confirm or retire it; no exclusivity, so no revenue to fund them from; and no innovator label, so the labelling changes when the monograph changes and not otherwise. The most informative modern data on this molecule — the brain receptor occupancy study, the cold meta-analysis, the anticholinergic cohort — were all produced by academics and public agencies, and none of them was required by anyone.
Source
Chlorpheniramine maleate marketed under over-the-counter monograph M012 (openFDA SPL application number field); Federal Food, Drug, and Cosmetic Act as amended in 1962
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
Checks this page had to pass
✓ Passed
Identity resolved
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✓ Passed
No unresolved merge across substance families
no quarantine open
✓ Passed
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.
✓ Passed
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.
What the approval register records
62 approved applications cover products containing this substance. The earliest was NDA006921, approved 19490713 to SCHERING.
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 first-generation H1 antihistamine that occupies 53.0% of cortical histamine receptors at the dose in a standard tablet, against 11.7% for loratadine, whose sedating and anticholinergic properties put its class among the three commonest contributors to a dementia signal at a hazard ratio of 1.54 for the heaviest users — and which is sold without any modern efficacy trial because it reached the market in 1949 and is grandfathered under an over-the-counter monograph.
Recorded evidence blocks (6)
Q1
On the CHLORPHENIRAMINE, (-)- label: indicated for what?
"Uses temporarily relieves these symptoms due to hay fever or other upper respiratory allergies: sneezing runny nose itchy, watery eyes itching of the nose or throat": indications and usage on CHLORPHENIRAMINE, (-)-'s label. DailyMed label · 7a3452a2-930f-48b1-8c59-dbceb10b9c78 · 2026-08-10
Q2
10 registered trials of CHLORPHENIRAMINE, (-)- — at which phases?
ClinicalTrials.gov — US Government work · 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: 5 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.