"Antidepressants were the third most common prescription drug taken by Americans of all ages in 2005–2008 and the most frequently used by persons aged 18–44 years. From 1988–1994 through 2005–2008, the rate of antidepressant use in the United States among all ages increased nearly 400%."

Source

Pratt, Laura A.; Brody, Debra J.; Qiuping, Gu,"Antidepressant Use in Persons Aged 12 and Over: United States, 2005–2008," NCHS data brief, no 76 (Hyattsville, MD: National Center for Health Statistics, 2011), p. 1.
http://www.cdc.gov/nchs/data/…