Promethazine is an antihistamine medication primarily used to treat Allergies, nausea, and motion sickness. It works by blocking histamine receptors in the body, which helps alleviate allergic symptoms and can also have sedative effects. Additionally, it is sometimes used as a preoperative sedative or to enhance the effects of pain medications. Promethazine is available in various forms, including tablets, syrups, and injections.