The analysis, published in the Journal of the American Medical Assocation, combined the findings of six different previous studies of two commonly prescribed treatments -- paroxetine, similar to common Paxil, Prosac and Zoloft, and imipramine, an older antidepressant drug.
"The magnitude of benefit of antidepressant medication compared with placebo increases with severity of depression symptoms and may be minimal or nonexistent, on average, in patients with mild or moderate symptoms. For patients with very severe depression, the benefit of medications over placebo is substantial," the study concluded.
The findings do not mean that the drugs or the placebos were frivolous for most users, "Good Morning America" chief medical editor Dr. Richard Besser said today. Rather, both the antidepressants and the placebos had a positive effect on the patients.
"You hear that headline and you think, 'Oh, my God, there is nothing out there that works for depression," Besser said. "The study actually found the exact opposite; that both placebo and medications were extremely effective at treating mild to moderate depression. What you can't tell from this study is what else is going on. Were these individuals getting what is most effective, which is talk therapy?"
The analysis included a pool of 434 patients from the antidepressant group and 284 patients in the placebo group.
Dr. Gary Kennedy, a professor of psychiatry and behavioral science at Montefiore Medical Center, Albert Einstein College of Medicine, said that analysis seemed logical, but was cautious of its conclusions.
"The finding that more severe depression is more likely to respond to antidepressant medication seems sound," Kennedy said. "But only six studies were used to generate the conclusion, and three of those studies used an antidepressant that few practicing physicians would prescribe nowadays.
"However... This is a major line of enquiry at present and offers the hope that we can prevent severe depression if we could identify the trajectory from minor to major depression," he said.
One criticism of the study is that by simply participating in the trial, the patients are getting a secondary form of therapy that is not measured: talk therapy.
"The most effective thing for mild to moderate depression is being in a therapeutic relationship where they can talk through their problems with someone who is really skilled," Besser said. "What they found in [the study], and you can't really tell from this, is that it didn't really matter the drug. You were getting better if you had this and that should give people hope with mild to moderate depression."
Harold Koenig, a professor of psychiatry and behavior sciences at Duke University Medical Center, said the study coordinators are often extremely kind and encouraging of participants to make sure they comply with the study.
"This is basically providing supportive therapy, and supportive therapy is very effective in mild to moderate depressions," Koenig said.
Several experts told "Good Morning America" that antidepressants are often prescribed to those with mild to moderate depression when proper therapy or interpersonal support is lacking.
"Consumers should understand that with mild or moderate depression, the ideal treatment must include talk therapy, ideally either cognitive-behavioral or interpersonal psychotherapy," said Dr. Ken Robbins, clinical professor of Psychiatry at the University of Wisconsin in Madison. "In addition, if antidepressants are to be used, it is best if they are prescribed by someone who has training and experience in the most up-to-date use of these medications."