Cyclizine

Cyclizine is a first-generation antihistamine used to prevent or treat nausea, vomiting, and motion sickness. It can cause drowsiness and other anticholinergic effects.

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Histamine H1 receptor: A receptor activated by histamine that mediates allergic responses and contributes to signaling in the brain. Cyclizine blocks H1 receptors involved in nausea and vestibular signaling.
Motion sickness: Nausea and related symptoms caused by a mismatch among sensory signals about movement. Preventing motion sickness is one of cyclizine’s established uses.
Meclizine: A first-generation antihistamine used chiefly to prevent and treat motion sickness and vertigo. It serves similar purposes, with use and availability varying by country.
Drowsiness: A state of reduced alertness and an increased tendency to fall asleep. Cyclizine can impair alertness, making driving and operating machinery unsafe for some people.
Muscarinic acetylcholine receptor: A family of receptors activated by acetylcholine and blocked by anticholinergic drugs. Cyclizine’s antimuscarinic activity contributes to its effects on motion-related nausea and its side effects.
Vertigo: A false sensation that oneself or the surroundings are moving or spinning. Cyclizine may be used to relieve nausea associated with vertigo.
Promethazine: A sedating first-generation antihistamine used for allergies, nausea, and other indications. It is another antihistamine option for nausea, but has a different adverse-effect profile.
Anticholinergic syndrome: A toxic state caused by excessive blockade of acetylcholine at muscarinic receptors. Large doses or interactions can intensify cyclizine’s anticholinergic effects.
Vestibular system: The inner-ear and brain pathways that detect head movement and help maintain balance and spatial orientation. Cyclizine dampens vestibular signaling that can trigger motion sickness.
Postoperative nausea and vomiting: Nausea or vomiting occurring after surgery, often related to anesthetic drugs and patient risk factors. Cyclizine is used in some settings to prevent or treat postoperative symptoms.