I have not taken these medications, but I am referencing my nurse's drug guide now. Ambien and Ambien CR are schedule IV medications. Ambien CR, or controlled release tablets are a CNS depressant, prescribed for relief of insomnia. The 12.5 mg CR tablet has 10mg released immediately, and then another 2.5 later. Be cautious (i.e., avoid) when combining ambien with other CNS depressants, such as opioid analgesics, alcohol, tricyclic antidepressants or antihistamines. Prolonged use of greater than 7 to 10 days can cause physical and psychological depenendence. If used for 2 weeks or longer, abrupt withdrawal may result in fatigue, nausea, flushing, light-headedness, uncontrolled crying, vomiting, GI upset, panic attack, or nervousness. Do not crush, break, or chew the tablet. Swallow whole.
The standard ambien tablets are exactly the same as above, except in 10mg tablets. No warning re: swallowing whole or not.
My medication of choice however, when I had difficulty sleeping was Trazodone. It is labeled as an anti-depressant, but also has unlabled uses for managing insomnia and chronic pain. The doses are different depending on its purpose. For insomnia, take 25-100mg at bedtime. For depression, its 150mg/day in 3 divided doses. The thing I like about trazodone better than medications like Lunesta or Ambien is that you can take the medication for your entire life and never build a tolerance to it. Ambien is really only intended for a week or two use at a time, and not for chronic insomnia.
This is a good link listing and describing the different "schedules" of medications. So when you ask if its a controlled substance, I'm not 100% sure what you are asking. Schedule I meds are like heroin and ecstasy, LSD. They have a high abuse potential, and no medical uses. Schedule II start the high abuse potential medications that have a medical use, like fentanyl, oxycodone, morphine, methadone, codeine, and cocaine. Schedule III are less abused, but still high risk, such as hydrocodone. Schedule IV, which includes Ambien, has a lower potential for abuse. You can have this kind of medication refilled five times within 6 months.
So to answer your question, "yes" it is a controlled substance, but it is so low on the list that it won't affect anything.
I guess I have too much free time! This is a little longer than I intended...I hope it helps ;)