sominex tablets have been formulated for those occasions when you cannot get to sleep because your natural routine is disturbed. sominex tablets contain promethazine hydrochloride, an antihistamine, which has a sedative effect. the medicine is used as a night time sleep aid, to correct temporary disturbances of sleep pattern where there is difficulty in going to sleep or staying asleep., a night time sleep aid, 16 one a night tablets, contains promethazine hydrochloride, decreases the time taken to fall asleep, increases the depth of slee