New research finds that 27 million Americans -- more than 10 percent of the population -- took antidepressant medications in 2005, double the number who reported taking such drugs in 1996, Reuters reported Aug. 3.

At the same time, fewer patients were seeking psychotherapy for depression, the researchers found, even though research has shown that therapy can be at least as effective as medication in treating depression.

Drugs like Paxil, which affect the brain's serotonin system and are known collectively as SSRI's, are the most commonly prescribed class of antidepressants. "Significant increases in antidepressant use were evident across all sociodemographic groups examined, except African-Americans," according to researchers Mark Olfson of Columbia University and Steven Marcus of the University of Pennsylvania. "Not only are more U.S. residents being treated with antidepressants, but also those who are being treated are receiving more antidepressant prescriptions."

Other studies have shown that 164 million prescriptions for antidepressants were written in the U.S. in 2008.

Olfson and Marcus speculated that the trend is due to a decline in stigma related to depression, the availability of new drugs to treat the disease, and a spike in direct-to-consumer advertising by pharmaceutical companies.

The research appears in the August 2009 issue of the Archives of General Psychiatry.