The shift is being made at the same time the Affordable Care Act, designed to improve access to health-care insurance, gets set to take effect next year.
The biggest factor behind the drop was the availability of lower-cost generic versions of drugs such as Pfizer's cholesterol-lowering Lipitor. New generics contributed $28.9 billion to last year's reduction in medicine spending.
The pharmaceutical industry has been grappling with an unprecedented "patent cliff" that ratings agency Fitch has estimated will mean the loss of more than $70 billion in revenue from brand-name medicines between the second half of 2011 and the end of 2015.
(Read More: Pfizer Earnings, Revenue Miss; Lowers Full-Year Guidance)
Last year's patent expiries also included Sanofi and Bristol-Myers Squibb heart drug Plavix, and AstraZeneca's antipsychotic, Seroquel.
Higher health costs and a weak economy have led many Americans to cut back on visits to the doctor. Admissions to hospitals also remained on the wane and the flu season in early 2012 was relatively mild.
"Patients are being influenced by higher out-of-pocket costs as employers seek to rein in insurance costs," Kleinrock said.
IMS also found that visits to emergency rooms increased 5.8 percent last year.
"Some choices that people are making may not be in everyone's best interest," Kleinrock said, noting that some emergency room visits could be by people putting off needed care.
U.S. health-care costs remain heavily concentrated among relatively few patients suffering from multiple chronic conditions, cancer, or other serious diseases.
Within the population of commercially insured people under the age of 65, 5 percent of them incurred 51 percent of total health-care costs—or $15,684 per person in 2012.