New-generation antidepressants may be no more effective than placebo for some patients with depression, analysis suggests.

A study published in the journal Public Library of Science Medicine focused on four selective serotonin reuptake inhibitors, namely Eli Lilly's Prozac; Effexor produced by Wyeth; Bristol-Myers Squibb's Serzone and GlaxoSmithKline's Paxil.

Forty-seven clinical trials submitted to the Food and Drugs Administration (FDA) were analysed.

Results showed that these drugs did not show clinically significant improvements for patients with moderate depression.

The most severely depressed patients did notice significant benefits from the drugs, however.

Lead researcher Irving Kirsch from Hull University said that the results showed "little reason to prescribe antidepressant medication to any but the most severely depressed patients, unless alternative treatments have failed to provide a benefit".

However in a statement, drugs firm Eli Lilly said: "Extensive scientific and medical experience has demonstrated that [Prozac] is an effective antidepressant."

GlaxoSmithKline spokesperson Mary Anne Rhyne said that the analysis had failed to acknowledge "very positive" benefits of the treatment.

"This analysis has only examined a small subset of the total data available while regulatory bodies around the world have conducted extensive reviews and evaluations of all the data available, and this one study should not be used to cause unnecessary alarm and concern for patients," she said.

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