Cyclizine

Cyclizine is a first-generation H₁ antihistamine of the ethanolamine class. In the vestibular apparatus of the inner ear and its associated central nervous system pathways, histamine released from histaminergic neurons can activate H₁ receptors in these regions and further stimulate the vomiting center in the brainstem. Cyclizine blocks H₁ receptors, reducing vestibular nerve responsiveness to motion stimuli and thereby preventing nausea and vomiting caused by motion sickness and seasickness. Cyclizine also antagonizes central and peripheral M₁ muscarinic receptors, suppressing the neural pathways from the vestibular system to the vomiting center and enhancing its anti-motion sickness and antiemetic effects.