The research, which analysed 47 clinical trials, breaks new ground by incorporating data not previously released by drug companies which researchers obtained under US freedom of information laws.
Its findings prompted some academics and mental health campaigners to question whether people with mild and moderate depression should be prescribed drugs like Prozac, which has been taken by 40 million people worldwide.
"The difference in improvement between patients taking placebos and patients taking anti-depressants is not very great," said Professor Irving Kirsch of Hull University, who led the team.
"This means that depressed people can improve without chemical treatments.
"Given these results, there seems little reason to prescribe antidepressant medication to any but the most severely depressed patients unless alternative treatments have failed to provide a benefit."
The study, published in the journal PLoS (Public Library of Science) Medicine, looked at Prozac, Seroxat, Effexor and Serzone and found the drugs were only better than a placebo for some people with severe depression.
Kirsch's team said it was one of the most thorough probes into the impact of new generation anti-depressants or selective serotonin reuptake inhibitors (SSRIs).
Drug companies strongly questioned the findings.
A spokesman for Eli Lilly, which makes Prozac, said that "extensive scientific and medical experience" had shown it is "an effective anti-depressant".
And GlaxoSmithKline, which makes Seroxat, said the study had not acknowledged the "very positive benefits" of the drugs.
"Their conclusions are at odds with what has been seen in actual clinical practice," a spokesman said.
"It is widely recognised by experts in the field that studies in depression are challenging and very difficult to conduct."
One leading academic who has studied why drug companies only publish some of their data on new drugs said in the wake of the findings they should be obliged to do so.
Doctor Tim Kendall, deputy director of the Royal College of Psychiatrists research unit, said the study was "fantastically important".
"I think it's too dangerous to allow drug companies -- where profit is a key factor -- to be able to withhold data which shows that a drug is ineffective or harmful," he said.
Alison Cobb, of mental health charity Mind, hailed the findings as "a serious challenge to the predominance of drugs in treating depression".
"Anti-depressants do help many people but by no means all and some people experience severe side-effects with them," she said.
"Nine out of 10 GPs say they've been forced to dish out drugs because they don't have proper access to 'talking treatments' such as cognitive behavioural therapy, which are recommended as the first-line treatment for mild to moderate depression."
Another mental health charity, Sane, warned the findings "could remove what has been seen as a vital choice for thousands," adding people should not stop taking their drugs immediately.
Güncelleme Tarihi: 26 Şubat 2008, 18:17