Cyclizine
H1 antihistamines
H1 antihistamines
A piperazine antihistamine anti-sickness medicine for nausea, vomiting, motion sickness and vertigo; on the WHO essential list.
Quick facts
- Group
- H1 antihistamines
- Target
- Histamine H1 receptor
- Used for
- Nausea and vomiting · Motion sickness · Vertigo
- Key effects
- Drowsiness · Dry mouth · Blurred vision
- Monitor
- Nausea and vomiting control · Sedation
- ATC
- R06AE03
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows doxepin, a tricyclic first-generation H1 blocker, in the human H1 receptor; cyclizine is thought to act at the same receptor.
Cyclizine is a first-generation H1 antihistamine with antimuscarinic action. It blocks histamine and acetylcholine signalling in the vestibular pathways and the vomiting centre, reducing nausea from motion, vertigo, surgery, opioids and some treatments. It causes drowsiness and anticholinergic effects such as dry mouth and blurred vision.
- Cyclizine blocks H1 and muscarinic receptors
- Vestibular signals to the brainstem are reduced
- The vomiting centre is less stimulated
- Nausea, vomiting and dizziness ease
Indications
- Nausea and vomiting, including after surgery or from opioids
- Motion sickness
- Vertigo, including Ménière's disease Ménière disease →
- Nausea and vomiting of pregnancy Hyperemesis gravidarum →
Adverse effects
Common
- Drowsiness
- Dry mouth
- Blurred vision
- Constipation or diarrhoea
- Headache
Contraindications
- Hypersensitivity to cyclizine
- Caution in severe heart failure, glaucoma and prostate enlargement
Key interactions
- Alcohol, benzodiazepines, opioids and other CNS depressants
- Additive sedation and slowed breathing
- Other anticholinergic drugs (tricyclic antidepressants, oxybutynin, antipsychotics)
- Additive dry mouth, urinary retention, constipation and confusion
What is monitored
- Nausea and vomiting control
- Sedation
- Heart rate and rhythm
Administration and safety
- Tablets by mouth; an injection is used in hospital
- For motion sickness it is taken before travel
Pregnancy and breastfeeding
Cyclizine can be used in pregnancy when needed, including for morning sickness; the clinician weighs risks and benefits.
Nursing care
- Assess nausea and vomiting before and after doses
- Teach not to drive or operate machinery until the effect is known, and to avoid alcohol
- Ask the patient to report palpitations, twitching or a rash
Pharmacokinetics
- Absorption
- Oral; also intramuscular or intravenous
- Metabolism
- Liver
- Onset and duration
- Within about an hour by mouth
Test yourself
Think of the answer, then tap the question to see it.
Which receptors does cyclizine block to reduce nausea?
Histamine H1 and muscarinic receptors.
In which two situations is cyclizine used?
Motion sickness and nausea after surgery (also vertigo and pregnancy sickness).
Why should a patient on cyclizine avoid driving if drowsy?
Cyclizine, a first-generation antihistamine, causes drowsiness and blurred vision.
Connections
← Back to the class: 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: Cyclizine: an anti-sickness medicine - NHS (NHS, 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.