A substance taken to prevent or treat nausea and/or vomiting. Antiemetic medications come in various forms. Anticholinergic agents (ACh blockers): Scopolamine: Antihistamine agents (H1 receptor blockers): Diphenhydramine (Benadryl), meclizine (Antivert), promethazine (Phenergan): Neuroleptic agents: chlorpromazine (Thorazine), prochlorperazine (Compazine): Prokinetic agents: Metoclopramide (Reglan): Serotonin blockers: Dolasetron (Anzemet), granisetron (Kytril), ondansetron (Zofran) and Tetrahydrocannabinoids: dronabinol (Marinol)