OBJECTIVES: To describe new data on recent trends in U.S. psychiatric prescription drug spending and utilization over the period 2003 to 2008 and to understand drivers of those new trends. METHODS: SAMSA Spending Estimates were coupled with MEPS data to examine trends in mental health drug spending and utilization through 2005.  1997-2008 Thomson Reuters MarketScan Commercial Claims data were used to decompose spending where: Total Expenditures = Price X Quantity, and ΔCost/Enrollee = ΔCost/Day  X  ΔDays/User X  ΔUsers/Enrollees. The following drugs were included in the analysis: Antidepressants, Antipsychotics, Stimulants, and Anxiolytic/Sedative/Hypnotics. RESULTS: The average annual growth rate in mental health prescription drug spending dropped from 28% in 1998 to 3% in 2008.  The rate of growth has stayed below 10% since 2005, and was negative in 2007.  For persons with private insurance, the average annual expenditure growth rate overall was 6% during the years 2001-2008, where 2% was attributable to days/user, 2% was due to users per population, and 2% was due to cost/day. In contrast for the years 1997-2001, the average growth rate overall was 18%, where  3% was attributable to days/user, 7% was due to users per population, and 8% was due to cost/day.  CONCLUSIONS: Mental health prescription drug spending growth has slowed in recent years.  This is due primarily to slower growth in additional users and slower price growth.  The lower price growth is mainly due to generic entries starting in 2005, particularly within the antidepressant drug class.