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 sleep