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Brompheniramine is a first-generation alkylamine H1 antihistamine structurally almost identical to chlorpheniramine, differing only by a bromine atom in place of chlorine. It relieves allergic symptoms by antagonizing histamine H1 receptors, and its ready central nervous system penetration produces the characteristic sedation of this drug class. In vitro binding studies show that it also blocks all five human muscarinic acetylcholine receptor subtypes with affinity comparable to chlorpheniramine, which underlies its anticholinergic side effects and places it among the deliriants. Because sedation and impaired psychomotor performance can occur even at therapeutic doses, brompheniramine has been repeatedly detected in forensic toxicology of transportation fatalities; large overdoses can precipitate a dangerous anticholinergic delirium.
- Relieves allergic rhinitis, hay fever and hives
- Eases runny nose, sneezing and itchy eyes in cold and allergy products
- Sedating effect can help allergy sufferers rest
- Blocks both H1 histamine and muscarinic receptors
- Drowsiness and reduced alertness
- Dry mouth, blurred vision and constipation
Mechanism
Brompheniramine is an / inverse at H1 receptors, which relieves allergic symptoms peripherally and causes drowsiness centrally because histamine normally supports wakefulness. As a first-generation antihistamine it crosses into the brain and also blocks receptors, producing the classic anticholinergic side effects and the deliriant profile at high doses. Being an alkylamine antihistamine, it shares the family's mild monoamine reuptake activity. When taken at high doses, the muscarinic blockade in the brain and body produces the full anticholinergic toxidrome.
receptor fingerprint
H1 receptorAntagonist (inverse agonist)
receptorsAntagonist
and transportersReuptake inhibitor
Safetyrisks and cautions, not medical advice
High doses of brompheniramine cause anticholinergic delirium with realistic hallucinations mistaken for reality, confusion and memory loss, along with the toxidrome: blurred vision, overheating, flushed dry skin, dry mouth, racing heart, urinary retention, seizures and, in severe cases, death. It shows up in combination cough and cold products, so it is easy to unknowingly stack it with other anticholinergics and pile on anticholinergic burden. High anticholinergic burden carries dementia-risk associations in the elderly and with long-term use. Not medical advice.
Interactionsdocumented pairs only, not exhaustive
Brompheniramine is a first generation H1 antihistamine, meaning it crosses into the brain and carries meaningful antimuscarinic activity, and nearly all of its interactions are additive rather than metabolic. Alcohol, benzodiazepines, opioids, barbiturates and sedating antidepressants stack with its sedation; alongside an opioid the additive respiratory depression matters, and the impairment on driving is larger than either drug alone would suggest.
Anticholinergic burden is the second axis. Tricyclics, oxybutynin, low potency antipsychotics and antiparkinsonian anticholinergics compound dry mouth, blurred vision, constipation and urinary retention, and in older adults that combination is a recognised precipitant of delirium.
Monoamine oxidase inhibitors prolong and intensify these anticholinergic effects, and because brompheniramine also inhibits serotonin and noradrenaline reuptake the pairing is treated as contraindicated. Brompheniramine is metabolised partly by CYP2D6, so strong inhibitors of that enzyme raise its concentration.
Checking a whole stack? Run it through interactions + stacks.
Subjective profileweighing the evidence above
Effective and cheap for allergy symptoms, but it is a sedating anticholinergic, which makes it a poor daily choice next to a second-generation antihistamine and a bad one in older adults. It hides in combination cold products, so it is easy to double up on anticholinergic burden without noticing.
Resources
This entry is here for reference.
Research
- 1981first citedSingle and repeated dose comparison of three antihistamines and phenylpropanolamine: psychomoto…
- 2024most recentClassics in Chemical Neuroscience: Deliriant Antihistaminic Drugs.
- 1.Affinities of brompheniramine, chlorpheniramine, and terfenadine at the five human muscarinic cholinergic receptor subtypes.
- 2.Classics in Chemical Neuroscience: Deliriant Antihistaminic Drugs.
- 3.Single and repeated dose comparison of three antihistamines and phenylpropanolamine: psychomotor performance and subjective appraisals of sleep.
- 4.First-generation H1 antihistamines found in pilot fatalities of civil aviation accidents, 1990-2005.
- 5.Histamine-induced venodilation in human beings involves both H1 and H2 receptor subtypes.
- 6.The eternal triangle: benefit, risk, and cost of therapeutic agents.
6 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
How is brompheniramine different from chlorpheniramine?
They are nearly the same molecule; brompheniramine has a bromine atom where chlorpheniramine has chlorine. Their effects, including the anticholinergic and deliriant risks, are very similar.
Is it safe because it is over the counter?
Over-the-counter does not mean risk-free. At high doses it causes a dangerous anticholinergic delirium, and it is easy to stack anticholinergic burden with other cold-product ingredients.
Does it make you sleepy?
Yes. Blocking brain histamine H1 receptors causes marked drowsiness, which is why it can impair driving and coordination.
Adverse effects
- Drowsiness and reduced alertness
- Dry mouth, blurred vision and constipation
Notes and cautions
- Urinary retention and confusion, especially in the elderly
- Delirium and toxidrome at high doses