Researchers report that cognitive therapy to treat moderate to severe depression works just as well as antidepressants and in some cases works better.

University of Pennsylvania researchers reported their findings in the Archives of General Psychiatry.

The team compared the efficacy of antidepressants with cognitive therapy in 240 moderately to severely depressed patients. Researchers randomly assigned study participants drugs, cognitive therapy or placebo.

They found response rates for study participants in both the drug and psychological therapy groups were 58 percent. However, those receiving cognitive therapy were less likely to have a relapse - 46 percent in the drug group, compared with 40 percent in the cognitive therapy group.

"For many people, cognitive therapy might prove to be the preferred form of treatment," wrote the researchers.

The findings challenge the American Psychiatric Association's guidelines that drugs are the only effective treatment for moderately to severely depressed patients.