The lowdown on sleeping pills

I think this is some really useful information. I found it in Mayoclinic.com.
Today's sleeping pills don't carry the same risks of dependence and lethal overdoses as sleeping pills of the past. But risks remain — especially for people who have certain medical conditions, including liver and kidney disease. Here's the lowdown on some of the most common types of sleeping pills used today.
Over-the-counter medications
Various over-the-counter sleeping pills are available in any pharmacy. Many of these medications contain antihistamines, which induce drowsiness by working against the central nervous system chemical histamine. They're most effective for an occasional sleepless night. The more often you take them, the less effective they become.
Nonbenzodiazepine hypnotic medications
Nonbenzodiazepine hypnotic medications are the newest class of sleeping pills. They quiet the nervous system, which helps induce sleep. They're metabolized quickly, which helps reduce the risk of side effects the next day. These medications are mainly intended for short-term or intermittent use. They're available by prescription only.
Benzodiazepine hypnotic medications
Benzodiazepines are an older class of sleeping pills. They're more likely than newer types to cause drowsiness or headaches the next morning, and they may become habit forming. Benzodiazepines are available by prescription only.
Sedating antidepressants
Sometimes drugs used mainly to treat depression may ease insomnia when taken in lower doses. When insomnia is secondary to depression or anxiety, antidepressants can improve both conditions at the same time. Antidepressants are available by prescription only.
source: mayoclinic.com