A new study of prescription antidepressants published this week suggests the drugs may be no more effective than placebo in treating the most common forms of depression.

“Although patients get better when they take antidepressants, they also get better when they take a placebo, and the difference in improvement is not very great,” said the study’s lead researcher Irving Kirsch, a professor of psychology at the University of Hull in Great Britain, in a prepared statement. “This means that depressed people can improve without chemical treatments.”

Kirsch and colleagues collected data on 35 clinical trials of antidepressant selective serotonin reuptake inhibitors (SSRIs) submitted to the FDA. Drugs in the trials included fluoxetine (Prozac), venlafaxine (Effexor), nefazodone (Serzone) and paroxetine (Paxil). 

According to Kirsch’s analysis of the data, patients taking the antidepressant drugs fared no better than patients taking placebo. The result appeared to be the same in patients who were mildly or moderately depressed. The antidepressants appeared to benefit a small group of patients with severe depression, the study found.

The findings were published online Feb. 25 in the journal PLoS Medicine. For more, information click here.

Global sales of antidepressants were approximately $21 billion in 2007.