GlaxoSmithKline was sued by the New York attorney general for 'illegal and deceptive' reporting of the risks of its anti-depressant Seroxat. Photograph: Jack Sullivan

Another pharmaceutical giant has settled a big compensation claim. So why are they allowed to go on misleading the public?

This week the drug company AstraZeneca paid out £125m to settle a class action. More than 17,500 patients claim the company withheld information showing that schizophrenia drug quetiapine (tradename Seroquel) can cause diabetes. So why do companies pay out money before cases get to court?An interesting feature of litigation is that various documents enter the public domain. This is how we know about the tobacco industry's evil plans to target children, the fake academic journal that Elsevier created for Merck's marketing department, and so on.

One of the most revealing documents ever to come out of a drug company emerged from an earlier quetiapine case: an email from John Tumas, publications manager at AstraZeneca. In it, he helpfully admits that they do everything I say drug companies do.

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