Antidepressants are no better than dummy drugs at treating depression in the majority of patients, a new study has concluded.
Researchers from the University of Hull say that 'new generation' antidepressants such as Prozac only benefit some, very severely depressed patients.
Makers of the drugs studied have urged caution over the research however, pointing to other reports that have been carried out on their efficacy.
For the latest study, published today in the journal PLoS Medicine, the researchers reviewed data on clinical benefit from trials submitted to the US Food and Drug Administration for the drugs Prozac (fluoxetine), Seroxat (paroxetine), Effexor (venlafaxine) and Serzone (nefazodone).
They included data from unpublished as well as published trials to avoid bias that may result from non-publication of disappointing findings.
The results showed that, compared to people receiving a placebo, the improvement in depression amongst patients receiving the trial drug was not clinically significant in mildly depressed patients or in most patients who suffer from very severe depression.
The only benefit of antidepressants was seen in a small group of patients who were the most extremely depressed.
This improvement seemed to come about, the researchers claim, because these patients did not respond as well as less depressed patients to placebo, rather than responding better to the drug.
"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 researcher Professor Irving Kirsch.
"This means that depressed people can improve without chemical treatments."
The researchers argue that there is little reason to prescribe new-generation antidepressant medications to any but the most severely depressed patients unless alternative treatments have been ineffective.
A spokesperson for GlaxoSmithKline, which makes Seroxat, said the study only analysed a "small subset of the total data available" and "should not be used to cause unnecessary alarm and concern for patients".