Ambien CR is different from Ambien in that it uses zolpidem tartrate extended release. The continued release allows for increased effectiveness of a lower, consistent dose of zolpidem, gives less or no hangover, and is proven to be more effective than traditional Ambien in quality of sleep (less/no sleep interruptions) and depth of sleep (preserves stage 3 and 4 deep sleep.) Ambien CR is also celebrated because it lacks many of the side effects for which non-CR Ambien is particularly notorious.