Sominex Tablets Sominex Tablets are a clinically proven sleep aid to relieve occasional sleeplessness. They contain promethazine hydrochloride, an antihistamine that has a sedative effect. Sominex Tablets are ideal for correcting temporary disturbances of your normal sleep pattern where you have difficulty in going to sleep or staying asleep, caused by changes to your normal routine e.g. jetlag. Sominex Tablets are suitable for adults & children over 16 years of age.