Though physical inactivity is clearly linked to prescription drug trends, poor mental health has also influenced usage patterns: Antidepressants were the third most-popular type of drug dispensed in 2008, with $9.5 billion in sales.

The percentage of non-elderly adults who used antidepressants increased from 6% to 10% between 1996 and 2005, according to Dr. Mark Olfson, a professor of clinical psychiatry at Columbia University Medical Center who recently analyzed these trends and published the findings in the Journal of the American Medical Association.

Olfson and his co-author, Steven C. Marcus, a professor at the University Pennsylvania School of Social Policy & Practice, found that the increase occurred regardless of gender, age, marital status, educational level and health insurance status.

Despite the increase in antidepressant use, Olfson says it’s unclear if the trend indicates that more Americans are struggling with mental health issues. Rather, Olfson cites the growing acceptance of discussing and treating depression and the use of antidepressants for conditions like insomnia and back pain as factors for the increase.