People in the United States took more prescription drugs than ever last year, with the number of prescriptions increasing from 3.99 billion (with a cost of $308.6 billion) in 2010 to 4.02 billion (with a cost of $319.9 billion) in 2011.

Those numbers and others appear in an annual profile of top prescription medicines published in the journal ACS Chemical Neuroscience.

Journal Editor-in-Chief Craig W. Lindsley analyzed data on 2011 drugs with a focus on medications for central nervous system (CNS) disorders. So-called antipsychotic medicines -- including those used to treat schizophrenia, bipolar disorder, obsessive-compulsive disorder, Tourette syndrome and some forms of depression -- ranked as the fifth most-prescribed class of drugs by sales. Antidepressants, for conditions that include depression and anxiety, ranked No. 7.

XanaxTM, CelexaTM and ZoloftTM were the most-prescribed psychiatric medicines, with other depression and anxiety medications rounding out the top 10. Two antipsychotics were among the 10 drugs that Americans spent the most on, with AbilifyTM in fourth place. Lindsley explains that while antidepressants continued to be the most-prescribed class of CNS drugs in 2011, prescriptions for ADHD medicines increased by 17 percent and multiple sclerosis medications by 22.5 percent in sales from 2010. While expiring patents on major antipsychotics in the next few years will put pressure on drug makers to innovate, the industry should be heartened by the growth of the number of prescriptions and spending.