The FDA is saying to lower the dosage recommendation, not the dosage. It's recommended people/women start with 5 instead of 10 (what it has been). If what you take works for you, nothing changes but if a new person decides to try Ambien, it's recommended (not law) on any information/packaging your doctor gets that they start with 5.

http://www.fda.gov/Safety/MedWatch/S.../ucm334738.htm