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Doug Krizner: The number of people taking anti-depressants worldwide has got to be astounding. In this country alone, it's estimated that 227 million prescriptions were written during 2006.

Well, now a new study shows many of these drugs don't significantly improve things for most patients. A team of researchers from the U.S., Britain and Canada have found drugs like Prozac work no better than a placebo. Not surprisingly, two of the drug companies concerned have dismissed these findings, as Stephen Beard reports from London.

Stephen Beard: The researchers looked at the four most widely used anti-depressants, including Prozac and Paxil. They reviewed data on 47 clinical trials. Some of that data was unpublished. The researchers used freedom of information laws to get access to it.

They concluded that in most cases, the drugs had more or less the same effect as placebos. The drugs only proved really beneficial for a small group of severely depressed patients.

GlaxoSmithKline, which makes Paxil and Eli Lilly, which makes Prozac, both rejected the study as insufficient.

But a spokesman for Britain's Royal College of Psychiatrists said the message was clear -- that drug companies must be compelled to publish all the data from their clinical trails.

In London, this is Stephen Beard for Marketplace.