Numark sleep aid 50mg tablets are used to relieve temporary sleeping difficulties. Numark sleep aid 50mg tablets are used to relieve temporary sleeping difficulties. The active ingredient is diphenhydramine hydrochloride, an antihistamine that causes sleepiness or drowsiness. Temporary difficulties in getting a good night's sleep can be caused by various problems such as stress, jet lag or personal problems such as bereavement. In sleep problems of this type, this medicine has been shown to help sufferers to fall asleep faster, have a longer and deeper sleep, and to wake up feeling rested in the morning. Do not take this medicine for more than 2 weeks without consulting your doctor.