American scientists say anti-depressants and sedatives such as Prozac may be at best only 25% more effective than placebos. Previous research suggested they could by up to 40% more effective.

Writing in the New Scientist, Irving Kirsch of the University of Conneticut and Guy Sapirstein of Westwood Lodge Hospital in Maaschusetts said they studied 2,318 patients, some of whom had taken placebos and some of who had been given anti-depressants.

Relief

Psychological evaluations of the patients not only showed that the anti-depressants were not as successful as previously suggested, but that their effectiveness could be explained by patients' relief at being diagnosed and believing their condition was treatable.

Over 3m people in the UK are thought to suffer from depression

They said some of the trial patients may have been used to the side effects of taking the drugs and realised they were being given antidepressants. This could have increased their expectations of their effectiveness.

The scientists also found that antidepressants were no better than old-style tranquillisers and other types of downers despite their manufacturers' claims and the high fashion status of drugs like Prozac.

Irving Kirsch said trials of the drugs needed to be more strictly controlled.

Uncertainty

Also writing in the New Scientist, Simon Wessely, professor of psychiatry at King's College Hospital in London, said: "There's a tremendous uncertainty about how [the drugs] work. The public thinks the doctors know, but they don't."