[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/) › Dimenhydrinate # Dimenhydrinate ## H1 antihistamines? H1 antihistamines A sedating H1 antihistamine (a salt of diphenhydramine) used to prevent and treat the nausea, vomiting and vertigo of motion sickness. Updated Nov 1, 2026 ## Quick facts **Group** [H1 antihistamines](https://durgical.com/en/pharmacology/classes/h1-antihistamines/) **Target** Histamine H1 receptor (and muscarinic receptors) **Used for** Prevention and treatment of nausea **Key effects** Drowsiness · Dizziness · Dry mouth **Monitor** Level of sedation · Urinary retention and confusion **ATC** R06AA11 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 (and muscarinic receptors)**Dimenhydrinate ⓘ The figure shows doxepin, a first-generation H1 blocker, in the human H1 receptor; diphenhydramine, the active part of dimenhydrinate, binds the same site. **Target in 3D:** Histamine H1 receptor (and muscarinic receptors). 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 Dimenhydrinate is the 8-chlorotheophylline salt of diphenhydramine, in about equal parts. Diphenhydramine blocks central H1 receptors and muscarinic receptors in the vestibular pathways and the vomiting centre. This damps the overstimulated signal from the inner ear that causes motion sickness. The same central H1 and antimuscarinic actions explain the drowsiness and the dry mouth. - Motion overstimulates the labyrinth and vestibular nuclei - Diphenhydramine blocks central H1 and muscarinic receptors - Vestibular input to the vomiting centre is damped - Nausea, vomiting and vertigo ease; drowsiness is expected ## Indications - Prevention and treatment of nausea, vomiting and vertigo of motion sickness ## Adverse effects ### Common - Drowsiness (most common) - Dizziness, headache, nervousness and insomnia - Dry mouth, nose and throat; blurred vision - Difficulty passing urine - Tachycardia, epigastric discomfort and rash ### Serious (rare, important) - Overdose: in children hallucinations, convulsions and death; in massive overdose coma and respiratory depression - Must never be injected into an artery ## Contraindications - Neonates (the injection contains benzyl alcohol, linked to the fatal gasping syndrome in premature infants) - Hypersensitivity to dimenhydrinate, diphenhydramine or 8-chlorotheophylline - Caution in conditions that anticholinergic drugs can worsen, such as narrow-angle glaucoma or prostatic enlargement ## Key interactions **Alcohol and other CNS depressants** Additive sedation and impaired driving **Certain antibiotics that can damage hearing** Dimenhydrinate may mask early ototoxic symptoms until damage is irreversible ## What is monitored - Level of sedation, especially in older adults - Urinary retention and confusion in older adults - Hearing symptoms in patients on ototoxic antibiotics ## Administration and safety - The injection is given intramuscularly or, after dilution in sodium chloride, slowly intravenously - Never injected into an artery - Parenteral solution is inspected for particles and discolouration - For motion sickness it is given before the journey ## Pregnancy and breastfeeding Human data do not show an increased risk of malformations, but it is used only if clearly needed; safety in labour is not established. ## Nursing care - Warn about drowsiness: no driving or machinery, and no alcohol - Raise bed rails and help older adults walk after a dose - Check for urinary retention and dry mouth - Keep out of reach of children: overdose is dangerous in them ## Pharmacokinetics **Absorption** Oral (tablets, chewable tablets, syrup) or injection (intramuscular or diluted intravenous) **Onset and duration** Used before travel to prevent symptoms, and also to treat them ## Memory aid DIMENhydrinate DIMs the inner ear (and the patient): good for motion, bad for driving. ## Test yourself Think of the answer, then tap the question to see it. ## What is dimenhydrinate chemically? The 8-chlorotheophylline salt of diphenhydramine. ## What is the most common adverse effect of dimenhydrinate? Drowsiness. ## Why is dimenhydrinate injection contraindicated in neonates? It contains benzyl alcohol, linked to the fatal gasping syndrome in premature infants. ## Which risk arises when dimenhydrinate is given with ototoxic antibiotics? It may mask early ototoxic symptoms until the damage is irreversible. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/dimenhydrinate/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) ## Connections ## Related drugs 3 - [Diphenhydramine](https://durgical.com/en/pharmacology/diphenhydramine/) - [Meclozine](https://durgical.com/en/pharmacology/meclozine/) - [Promethazine](https://durgical.com/en/pharmacology/promethazine/) [← 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: [DailyMed - DIMENHYDRINATE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=bc71539e-1a33-4709-8a24-c2894e8dbc1c) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=R06AA11) (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/dimenhydrinate/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/dimenhydrinate/