(Chicago Daily Herald) -- The number of Americans taking antidepressants doubled to 10.1 percent of the U.S. population in 2005 compared with 1996, increasing across income and age groups, a study found.

An estimated 27 million U.S. people ages 6 and older were taking the drugs by 2005, while their use of psychotherapy declined, according to Columbia University research published in the August issue of the Archives of General Psychiatry.

The surge in antidepressant use propelled that class of treatments to become the top-selling U.S. medicines in 2005, surpassing blood-pressure prescriptions, the study said.

Rising use of the drugs "may involve the introduction of new antidepressants, the increase in the direct-to-consumer advertising, lessening stigma with seeking mental health care" and more Americans acknowledging they are depressed, said lead author Mark Olfson, a professor of clinical psychiatry at Columbia University and New York State Psychiatric Institute in New York.

The trend fueled sales of such antidepressants as Eli Lilly & Co.s Prozac, Forest Laboratories Inc.s Celexa and Pfizer Inc.s Zoloft. The research found more growth in the class of antidepressants known as selective serotonin reuptake inhibitors and a decline in tricyclic antidepressants.

The results also showed a jump in the use of antidepressants across demographic groups, with the exception of blacks. The rate of use of the medicines among blacks in 2005 was 4.5 percent, less than half that of whites. The rate for Hispanics increased to 5.2 percent in 2005 from 3.7 percent in 1996.

Olfson said its unclear if more people are depressed or if more people are just taking antidepressants. Other studies have found diagnoses of major depression in adults increased from 3.3 percent in 1991-1992 to 7.1 percent in 2001-2002.

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