Prozac, the bestselling antidepressant taken by 40 million people worldwide, does not work and nor do similar drugs in the same class, according to a major review released today.

The study examined all available data on the drugs, including results from clinical trials that the manufacturers chose not to publish at the time. The trials compared the effect on patients taking the drugs with those given a placebo or sugar pill.

When all the data was pulled together, it appeared that patients had improved - but those on placebo improved just as much as those on the drugs.

The only exception is in the most severely depressed patients, according to the authors - Prof Irving Kirsch from the department of psychology at Hull University and colleagues in the US and Canada. But that is probably because the placebo stopped working so well, they say, rather than the drugs having worked better.