The report, commissioned by drug maker Sanofi Aventis, suggests that employers would benefit from better treatments of their workers for depression. Depression is the leading cause of disability among Americans aged 15 to 44, according to the National Institute of Mental Health.

Even when depressed patients are treated with antidepressants, there are substantial productivity losses. Therapies that can better manage depression may provide opportunities for savings to employers, the Thomson Reuters research team wrote in the Journal of Occupational and Environmental Medicine.

Despite the widely acknowledged effectiveness of antidepressant therapy, productivity costs related to depression persist even after patients receive treatment, Suellen Curkendall, director of outcomes research at Thomson Reuters, said in a statement.

This may be due to the fact that patients often don't respond to the first type of antidepressant that they are prescribed. They also may fail to take their medications on a regular basis, added Curkendall, who led the study.

Curkendall and colleagues analyzed insurance claims and employee health and productivity data for more than 22,000 patients treated with antidepressants and compared them to people without depression.

Workers who had been treated for depression were twice as likely as others to use short-term disability leave, they found. Disability-related costs for a year, on average, were $1,038 for patients treated for depression and $325 for the non-depressed workers.

Over 40 percent of patients with depression were diagnosed with at least one of the other included psychiatric conditions besides depression, the researchers at Thomson Reuters, parent company of Reuters, added.

Most common were anxiety, dissociative and so-called somatoform disorders -- a group of disorders with physical symptoms but no apparent physical cause.

Last month, a team at the University of Pennsylvania found only patients with very severe depression were measurably helped by antidepressant drugs. Mild to severe depression might be better treated with alternatives to antidepressant drugs, they wrote in the Journal of the American Medical Association.

At least 27 million Americans take antidepressants and more than 164 million prescriptions for antidepressants were written in 2008, totaling nearly $10 billion in U.S. sales and $20 billion globally, according to IMS Health.

(Reporting by Maggie Fox, editing by Jackie Frank)

Depression