In the ongoing effort to find the best method to treat severe depression, a combination of both therapy and antidepressant medications appears to work best to relieve suffering, but only if the affliction has been short-term, researchers say.

In a study with more than 450 patients over almost four years, half the study group was treated with a combination of cognitive therapy and drugs while the other half was treated with antidepressant medications alone.

Four out of five patients afflicted with severe depression for less than 2 years experienced a full recovery when their treatment consisted of the combined therapies, the researchers found.

"We think antidepressants work from the bottom up on the brain, smoothing hyperactivity in the area near the brain stem where emotions are generated," says lead study author and psychiatry Professor Steven Holland at Vanderbilt University. "And cognitive therapy may work from the top down in the frontal cortex. You learn you're more controlled than you thought you were."

However, in patients suffering from mild depression or those with sever chronic depression for more than 2 years, such a combined therapy was no more effective than a course of drug treatments alone, the researchers found.

"Our findings suggest that CT (cognitive therapy) engages different mechanisms than ADM (antidepressant medication) but that it likely does so only in some patients," Holland says.

Cognitive therapy is a form of treatment intended to deal with the kinds of thoughts that can lead to self-destructive behavior, according to the National Alliance on Mental Illness.

There is growing agreement in the medical field that patients suffering from depression require more than just medications to treat their symptoms, which is why cognitive therapy is seen more and more and as appropriate additional consideration, the researchers said.

Still, there are hurdles to overcome, and findings like those of the current study could aid mental health specialists in providing the accessible resources to patients most likely to gain from them, says Dr. Scott Krakower, assistant chief of psychiatry at New York's Zucker Hillside Hospital.

"It could help us figure out who needs therapy acutely and who will benefit most from medication, because it's so hard to find a therapist," he says.

One in 10 adults in the United States suffers from severe depression, the Centers for Disease Control and Prevention estimates.

The study has been published in the journal JAMA Psychiatry.