Ambien is a drug used for sleep initiation for people with insomnia. It works by making one feel woozy in a relatively short period of time after dosing with the hopes of doing its job quickly and knocking the user out so he or she can get a good night sleep. At this time Ambien is not an illegal drug in Pennsylvania so there is nothing that prohibits the operator of a motor vehicle from having it in their system while driving. But this does not mean that Ambien is safe to use when operating a car, and I have gotten cases recently where the driver has been charged with DUI for being under the influence of Ambien while driving. This is how it works.
Ambien is technically classified as a “nonbenziodiazepine hyponotic” – whatever the hell that is. When a person takes it they can shortly enter into a haze, stupor, or hypnotic state that precedes sleep. 
Think how you feel when you take a lot of Nyquil or Benadryl. This is when a person cannot drive. People have been pulled over – and are now being prosecuted – for DUI while driving after taking Ambien and while in this impaired state. So, if you are taking Ambien, which by all accounts can be a very effective drug for what it is prescribed for, do not try and drive while on it. There could be trouble. To put it as clearly as possible – it is against the law to drive when you are feeling the effects of Ambien. Be advised.