Americans are taking a "startling" amount of mental-health related medications, according to a big new study by Medco Health Solutions. More than 1 in 5 Americans now takes at least one drug to treat a psychological disorder, ranging from antidepressants like Prozac to anti-anxiety drugs like Xanax. Understanding why Americans are taking more pills to treat mental illness "is the next critical goal," says Dr. Martha Sanjatovic in a statement released by Medco. Here's a look this growing trend, by the numbers:

2.5 million
The number of Americans surveyed for prescription drug use from 2001 to 2010

1/5
One out of every five U.S. adults takes drugs to treat some type of mental health condition

22
Percent increase in the number of U.S. adults taking mental health drugs in 2010 compared to 2001

29
Percent increase in the number of women using antidepressants in 2010 compared to 2001

1/5
Proportion of women over the age of 20 who are prescribed antidepressants, like Zoloft and Lexapro 

11
Percent of middle-aged women using anti-anxiety medications

5.7
Percent of middle-aged men using anti-anxiety medications

3
Number of people ages 20 to 44 using antipsychotic drugs (like Resperadol) and ADHD medications (like Ritalin) in 2010 for every one person who used them in 2001

100
Percent increase in the number of  children under age 10 taking antipsychotic medications

40
Percent increase in the number of girls being prescribed ADHD medications

23
Percent of people in the "diabetes belt" states of Tennessee, Kentucky, Mississippi, and Alabama who are on at least one psychiatric drug, according to the AP

Sources: Associated Press, Daily Beast, Huffington Post, LA Times