To prevent motion sickness, take promethazine the night before a long journey. Some products can be taken 1 to 2 hours before travelling, if it's a short journey. Promethazine, sold under the brand name Phenergan among others, is a first-generation antihistamine, sedative, and antiemetic used to treat allergies, nausea, and vomiting. Promethazine is an antihistamine medication that prevents and treats the symptoms of an allergic reaction. It can also help you relax, go to sleep and relieve nausea, vomiting or pain before or after procedures. Detailed Promethazine dosage information for adults and children. Includes dosages for Allergic Rhinitis, Nausea/Vomiting, Allergic Reaction and more; plus renal, liver and dialysis adjustments. Promethazine is a medicine used to help with allergy symptoms, reduce or prevent nausea and vomiting, or provide sedative or pain-relieving effects after surgery. View promethazine hydrochloride information, including dose, uses, side-effects, renal impairment, pregnancy, breast feeding, contra-indications and important safety information. Promethazine is used to treat allergy symptoms such as itching, runny nose, sneezing, itchy or watery eyes, hives, and itchy skin rashes. It also prevents motion sickness, and treats nausea and vomiting or pain after surgery. It is also used as a sedative or sleep aid. Promethazine is used to prevent and treat nausea and vomiting. Learn about side effects, drug interactions, dosages, warnings, and more. Find out how promethazine treats hay fever and other allergy symptoms and how to take it. NHS medicines information on promethazine – what it's used for, side effects, dosage and who can take it. Promethazine is used to relieve or prevent the symptoms of hay fever, allergic conjunctivitis (inflammation of the eye), and other types of allergy or allergic reactions.