Dr. Michael Thorpy and Dr. Shelby Freedman Harris of the Montefiore Medical Center Sleep Disorders Center want to clear up some things about using sleeping pills for insomnia.
Some drugs known as Z-drugs or hypnotics affect the GABA receptor in the brain. These drugs reduce arousal, making it possible for the individual to sleep. Some non-GABA sleeping pills affect the receptor for melatonin which also reduces arousal.
It's important that the reasons for insomnia in the particular individual be understood before they are given drugs to make sure it is an appropriate treatment.
"Sleeping pills should be taken only immediately before bedtime. It is not recommended they be taken in the middle of the night if you have to get up early the next morning. Some pills have a longer duration of effect than others and could cause daytime sedation. As with all prescription medications, sleeping pills need to be taken according to the physician’s recommendations."
http://consults.blogs.nytimes.com/2010/07/16/are-sleeping-pills-addictive/?WT.mc_id