Originally Posted by Christopher

Night Nurse is a brand; it contains promethazine, dextromethorphan, and paracetamol. It is the promethazine (an anti-histamine) that aids sleep, though dextromethorphan (an anti-cough agent) has some tranquillising effects as well, but these fade into insignificance beside those of promethazine. So if you can find promethazine available over the counter or in a cold or cough preparation, it should do the same job for you.