Also, direct to consumer antidepressant ads nearly quadrupled during the years of the study.
The study indicates that 10 percent of Americans, about 27 million people, were taking antidepressants in 2005.
Some experts say more Americans are acknowledging they are depressed, but researchers at Columbia University say the majority of children and adults studied weren't being treated for depression.
Half of those taking the drugs used them for back pain, sleep difficulties and other problems.
Most of the patients were prescribed the medications by doctors other than psychiatrists.
Studies also suggest doctors should be cautious about prescribing antidepressants to children because they may increase the risk of suicides among kids.
Researchers are concerned about the decline in patients seeking psychotherapy and say the findings highlight the need for doctors who aren't psychiatrists to get more training in mental health.