What is Ambien and what are its known side effects?

The drug is one of the most commonly used prescription sleep aids.

Another tweet she wrote said she was "not giving excuses for what I did(tweeted) but I've done weird stuff while on ambien- cracked eggs on the wall at 2am etc."

So what exactly is Ambien?

Ambien is the brand name for the drug zolpidem tartrate. It is part of a class of drugs called sedative-hypnotic, known to depress the central nervous system and promote sleep. It is also a schedule IV controlled substance under federal regulation because it can be abused or lead to dependence.

When is Ambien prescribed?

What are the most common side effects?
Four percent of users reported side effects over the first 10 nights, including drowsiness, dizziness and diarrhea. The higher the dose, the higher the risk of side effects.

What are the serious side effects of Ambien?
Ambien does have more serious physical risks, reported in about one percent of users in studies. These risks include allergic reactions like swelling of the tongue or throat, trouble breathing, nausea and vomiting.

What about behavioral side effects?
Ambien can cause abnormal thinking, behavioral changes and affect complex behaviors like driving a car. Less than one percent of people in studies reported sleep-driving, sleep-walking, preparing and eating food, talking on the phone, having sex and having hallucinations while not fully awake, according to Sanofi-Aventis -- and they do not usually remember these events.

Since Ambien is a central nervous system depressant, its use can also decrease alertness and ability to walk. It is known to cause falls and lead to hip fractures. Studies show poor recall after waking.

Sima Patel, M.D., is a third-year physical medicine and rehabilitation resident at the University of Minnesota who works in the ABC News medical unit.