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Medical Uses: – Doxylamine is used to treat cold or allergy symptoms like sneezing, runny nose, and hives. – It is also used for short-term […]

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Medical Uses:
– Doxylamine is used to treat cold or allergy symptoms like sneezing, runny nose, and hives.
– It is also used for short-term treatment of insomnia.
– Doxylamine is part of the first-generation sedating antihistamines widely used for insomnia.
– Evidence on the effectiveness of doxylamine for insomnia treatment is limited.
– Over-the-counter antihistamines like doxylamine are not recommended for chronic insomnia.

Morning Sickness:
– Doxylamine is used in combination with pyridoxine to treat morning sickness.
– It is the only FDA-approved medication for morning sickness.
– The combination drug is available under various brand names.
– Doxylamine succinate is the form used in medical treatment.
– Doxylamine alone is available over-the-counter, while the combination is prescription-only.

Forms and Availability:
– Doxylamine succinate is available in various forms, including immediate-release oral tablets.
– It is available alone and in combination with pyridoxine.
– Different dosages of doxylamine succinate are available in oral tablets and capsules.
– The combination with pyridoxine is available in extended-release tablets.
– Doxylamine is also found in over-the-counter cold medicine products.

Safety and Side Effects:
– Doxylamine has a fetal safety rating of A, indicating no evidence of risk.
– Common side effects include dizziness, drowsiness, dry mouth, blurred vision, and constipation.
– Long elimination half-life can cause next-day effects like grogginess.
– Tolerance to antihistamines can lead to rebound insomnia.
– Continuous use is associated with cognitive decline in older individuals.

Overdose, Pharmacokinetics, and Chemistry:
– Doxylamine is generally safe for healthy adults at recommended doses.
– The median lethal dose in humans is estimated to be 50-500mg/kg.
– Symptoms of overdose may include seizures, hallucinations, and death.
– Pharmacokinetic details: bioavailability, elimination half-life, metabolism.
– Chemistry: belongs to ethanolamine class of antihistamines, with similar members like bromodiphenhydramine and diphenhydramine.

Doxylamine (Wikipedia)

Doxylamine, sold under the brand name Unisom among others, is an antihistamine medication which is used in the treatment of insomnia and allergies. It is also used to treat morning sickness in pregnant women in combination with pyridoxine (vitamin B6). Doxylamine is available over-the-counter, and is used in nighttime cold medicines, such as NyQuil, as well as in pain medications containing acetaminophen and codeine, to help with sleep. The medication is taken by mouth.

Skeletal formula of the doxylamine molecule
Ball-and-stick model of the doxylamine molecule
Clinical data
Trade namesUnisom, Vicks Formula 44 (in combination with Dextromethorphan), others
  • AU: A
  • A (Briggs)
Routes of
By mouth
ATC code
Legal status
Legal status
  • AU: S3 (Pharmacist only)
  • US: OTC
Pharmacokinetic data
BioavailabilityOral: 24.7%
Intranasal: 70.8%
MetabolismHepatic (CYP2D6, CYP1A2, CYP2C9)
Elimination half-life10–12 hours (range 7–15 hours)
ExcretionUrine (60%), feces (40%)
  • (RS)-N,N-dimethyl-2-[1-phenyl-1-(pyridin-2-yl)ethoxy]ethan-1-amine
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard100.006.742 Edit this at Wikidata
Chemical and physical data
Molar mass270.376 g·mol−1
3D model (JSmol)
  • n1ccccc1C(c1ccccc1)(C)OCCN(C)C
  • InChI=1S/C17H22N2O/c1-17(20-14-13-19(2)3,15-9-5-4-6-10-15)16-11-7-8-12-18-16/h4-12H,13-14H2,1-3H3 checkY

Side effects of doxylamine include dizziness, drowsiness, grogginess, and dry mouth, among others. Doxylamine is an antihistamine—specifically an inverse agonist of the histamine H1 receptor—and to a lesser extent an anticholinergic—specifically an antagonist of the muscarinic acetylcholine receptors M1 through M5. It is a first-generation antihistamine and crosses the blood–brain barrier into the brain, thereby producing centrally mediated sedative and hypnotic effects.

Doxylamine was first described in 1948 or 1949. Several of the first-generation antihistamines, including doxylamine, are the most widely used sleep medications in the world. Doxylamine is also a potent anticholinergic, which means it also works as a deliriant at much higher than recommended doses as a result. Its sedative and deliriant effects have led to some cases of recreational use.

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