Antidepressants may only be effective in severely depressed patients, according to a new British study suggesting most patients see a similar improvement whether taking pills or placebos.

"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 Irving Kirsch, one of the study's authors.

In a new study, British researchers found most patients see a similar improvement whether taking antidepressant pills or placebos.
(CBC)

"This means that depressed people can improve without chemical treatments."

Researchers at the University of Hull in the U.K. analyzed drug efficacy data provided to the U.S. Food and Drug Administration for Prozac (fluoxetine), Effexor (venlafaxine), Serzone (nefazodone) and Seroxat/Paxil (paroxetine).

Published and unpublished trials were reviewed to prevent bias.

The 47 trials, which usually lasted six weeks, involved one group of patients taking a placebo or dummy pill, and another group receiving the anti-depressant. Depressive symptoms of both sets of patients were documented at the end of each trial.

The researchers found that the improvement in patients taking the antidepressants versus the dummy pills was not clinically significant in patients with mild or moderate depression, and even in many of the severely depressed patients.

"We find that the overall effect of new-generation antidepressant medication is below recommended criteria for clinical significance," the authors wrote in the study, published Monday in the journal PloS Medicine.

The researchers found that response to placebo in these trials was very large, "duplicating more than 80 per cent of the improvement observed in the drug groups," according to the study.

The authors suggested new generation antidepressants may be prescribed to severely depressed patients when previous alternative approaches have failed.