[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/) › Doxylamine # Doxylamine ## H1 antihistamines? H1 antihistamines A sedating first-generation antihistamine: an over-the-counter sleep aid and, with pyridoxine, a treatment for nausea and vomiting in pregnancy. Updated Nov 12, 2026 ## Quick facts **Group** [H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/) **Target** Histamine H1 receptor **Used for** Short-term relief of occasional insomnia **Key effects** Drowsiness the next day · Dry mouth · Headache **Monitor** Daytime sleepiness and falls **ATC** R06AA09 No doses: the clinician sets them by the current guideline. On this page - The basics Mechanism of action - Indications - Adverse effects - Pharmacokinetics - Memory aid - Safety Contraindications - Key interactions - What is monitored - Administration and safety - Pregnancy and breastfeeding - Nursing care - Study Test yourself - Connections Connections ## Mechanism of action ◎**Histamine H1 receptor**Doxylamine ⓘ The figure shows doxepin, a first-generation H1 blocker, in the human H1 receptor; doxylamine binds the same site (no doxylamine structure is available). **Target in 3D:** Histamine H1 receptor. PDB structure 3RZE (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/3RZE) · Drag to rotate · pinch to zoom Doxylamine, an ethanolamine antihistamine, crosses into the brain and blocks (as an inverse agonist) H1 receptors of the histamine wake-promoting system, causing drowsiness. It also blocks muscarinic receptors, which explains the dry mouth, blurred vision and urinary retention. H1 and muscarinic block in the vestibular and vomiting pathways reduce nausea; combined with vitamin B6 (pyridoxine) it is used for nausea and vomiting of pregnancy. - Enters the brain and blocks H1 receptors - Histamine wake signal falls: drowsiness - Muscarinic block: dry mouth, urinary retention - With pyridoxine: less nausea in pregnancy ## Indications - Short-term relief of occasional insomnia (over the counter) [Insomnia disorder →](https://durgical.com/en/conditions/insomnia-disorder/) - Nausea and vomiting of pregnancy, with pyridoxine [Hyperemesis gravidarum →](https://durgical.com/en/conditions/hyperemesis-gravidarum/) - Ingredient of night-time cold and flu combinations ## Adverse effects ### Common - Drowsiness the next day - Dry mouth, nose and throat - Headache, dizziness, restlessness - Constipation or stomach upset ### Serious (rare, important) - Difficulty passing urine - Blurred vision or dilated pupils - Confusion, fast or irregular heartbeat, seizures (more likely in overdose and older people) ## Contraindications - MAO inhibitors now or within two weeks (pyridoxine combination) - Caution or avoidance in glaucoma, urinary retention from prostate enlargement, asthma, peptic ulcer or bowel obstruction - Generally avoided in people aged 65 or older; safer options exist ## Key interactions **Alcohol and other CNS depressants** Much more drowsiness. **MAO inhibitors** Listed as a precaution with the pyridoxine combination; the combination is avoided. **Other anticholinergic drugs** Additive dry mouth, constipation, urinary retention and confusion. ## What is monitored - Daytime sleepiness and falls - Urinary retention and constipation - Duration of use for insomnia (short-term only) ## Administration and safety - Sleep aid: taken about half an hour before bedtime, with enough time for a full night's sleep; for short-term use only. - Pregnancy tablet (with pyridoxine): taken at bedtime on an empty stomach, swallowed whole, not crushed or split. - Not combined with other products that contain an antihistamine. ## Pregnancy and breastfeeding With pyridoxine it is a treatment for nausea and vomiting of pregnancy; the combination is not taken while breastfeeding. ## Nursing care - Before: ask about glaucoma, prostate problems, asthma and age over 65. - During: warn about next-day drowsiness; no driving until the effect is known. - Teach to avoid alcohol and to report difficulty urinating or blurred vision. - Advise a review if sleep problems last more than two weeks. ## Pharmacokinetics **Absorption** Oral; the pyridoxine combination is a delayed- or extended-release tablet. **Onset and duration** As a sleep aid it is taken shortly before bedtime. ## Memory aid DOXYlamine makes you DOZY: H1 block for sleep, plus B6 for morning sickness. ## Test yourself Think of the answer, then tap the question to see it. ## Why does doxylamine cause sleepiness? It crosses into the brain and blocks H1 receptors of the histamine wake system. ## Which vitamin is combined with doxylamine for morning sickness? Pyridoxine (vitamin B6). ## Why is doxylamine usually avoided in older adults? Its anticholinergic and sedative effects cause confusion, falls and urinary retention. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/doxylamine/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) ## Connections ## Related drugs 4 - [Diphenhydramine](https://durgical.com/en/pharmacology/diphenhydramine/) - [Pyridoxine](https://durgical.com/en/pharmacology/pyridoxine/) - [Promethazine](https://durgical.com/en/pharmacology/promethazine/) - [Meclozine](https://durgical.com/en/pharmacology/meclozine/) ## Related conditions 2 - [Insomnia disorder](https://durgical.com/en/conditions/insomnia-disorder/) - [Hyperemesis gravidarum](https://durgical.com/en/conditions/hyperemesis-gravidarum/) [← Back to the class: H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Doxylamine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682537.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Doxylamine and Pyridoxine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a613045.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Structure of the human histamine H1 receptor in complex with doxepin](https://www.rcsb.org/structure/3RZE) (RCSB Protein Data Bank, 2011); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=R06AA09) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/doxylamine/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/doxylamine/