Seroquel brings in almost 10% of AstraZeneca's revenues
The marketing team sued over a drug's alleged side effects tried to suppress key data, an ex-employee has claimed.
Seroquel's former UK medical adviser told the BBC he was pressured to approve promotional material which said weight gain was not an issue.
Maker AstraZeneca, which faces fresh legal action next month, said it took concerns about its conduct seriously.
In the same programme, the British Medical Journal editor urged that the medicine licensing system be reviewed.
Dr Fiona Godlee said industry should no longer provide the evaluations of its own drugs which the licensing body considered.
Thousands of patients are suing AstraZeneca in US courts, claiming the anti-psychotic drug Seroquel caused weight gain and diabetes.
The patients allege Seroquel, its second biggest selling drug worth $4.5bn (£2.7bn) a year, was marketed without adequate warning about possible side effects such as massive weight gain and the development of diabetes. However, this is denied by the company.
AstraZeneca, which is facing renewed legal action next month, said the company took concerns about its conduct seriously.
Seroquel was launched in 1997 for treating schizophrenia and later for bipolar disorder. Dr John Blenkinsopp, the company's former UK medical manager, claimed he was pressurised by the company's marketing arm to approve claims about the drug which he felt did not reflect the medical evidence.
"The clinical studies at the time of the launch of Seroquel showed patients developed significant weight gain, significant both statistically and clinically," he told the BBC's File on 4.
"They [the marketing team] came at me with a number of potential claims all of which were trying to intimate that Seroquel was not associated with weight gain - the data pointed in the opposite direction," added Dr Blenkinsopp who was speaking publicly for the first time since he left the company in 2000.
He said: "I understood where they were coming from. I had some robust discussions and exposed them to the data but that didn't seem to stop them because they were desperate for a differential advantage over one of the competitor products and they didn't have one.
"In the end I was put under quite a significant amount of pressure by the marketeers to sign off claims with regards to the lack of weight gain and I was unwilling to sign that off. The marketeers made it clear it could be career limiting for me," Dr Blenkinsopp added.
In the US the drug was marketed with claims that it would not cause weight gain. That was not done in the UK except for one advertisement, published in the British Journal of Psychiatry in April 2004.
Astra Zeneca said it would not comment specifically in reference to its former employees, but said it took seriously any concerns regarding the firm's conduct and compliance procedures and it was currently reviewing issues raised by File on 4's investigation.
It said Seroquel was an important medicine and its safety and efficacy has been evaluated in clinical trials with thousands of patients
Dr Godlee, Editor of the British Medical Journal, told File on 4 that the system of developing and licensing drugs needed a major overhaul to give an independent evaluation of the effects of medications.
She said the pharmaceutical industry had grown enormously and delivered many good and effective drugs. But she warned that its power and influence needed to be controlled.
She has called for independent trials for all new drugs. At present, the regulator - the Medicines and Healthcare products Regulatory Authority - has to rely on research provided by the drug companies when it licences a medicine.
Dr Godlee said the regulator could sometimes be swamped by the amount of information it was given.
The MHRA says it has seen no evidence of this and maintains it carries out thorough and detailed reviews of any application.
File on 4 is on BBC Radio 4 on Tuesday, 26 January , at 2000 GMT, repeated Sunday, 31 January, at 1700 GMT. You can also listen via the BBC iPlayerafter broadcast or download the podcast.
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