Lawyers representing patients who insist the bestselling drug is addictive have issued the first of 600 High Court writs against the company, each seeking compensation of up to £50,000.
Since first prescribed in Britain in 1990, Seroxat has been linked to at least 50 suicides of adults and children.
GSK, which makes up to £1billion a year from the drug, is already embroiled in lawsuits with American users, and has been accused of failing to act on warnings that it could have serious side-effects, including mood swings and personality changes.
Mark Harvey, of law firm Hugh James, claims Seroxat is “defective” under the 1987 Consumer Protection Act.
He said: “When patients took the drug, not only was there no warning of withdrawal problems, there was also a statement on the data sheet until about 2003 which said you cannot be addicted to Seroxat.
“Unfortunately many people are havingdifficulties as they try to withdraw from the drug, and there are a few who have not been able to stop taking it.”
Earlier this year the BBC’s Panorama programme alleged that GSK had covered up fears about Seroxat’s safety, which the firm strongly denied.
The drug was banned for under-18s in 2003 amid concerns that it contributed to suicide among adolescents with depression, and adult patients have reported that, when they stop taking it, they feel aggressive, reckless and violent towards themselves.
Four years ago a man arrested for armed robbery was cleared after medical experts concluded that his behaviour could have been altered by severe withdrawal symptoms from Seroxat.
GlaxoSmithKline said: “Seroxat has benefited millions of people worldwide.
“We believe the product is not defective and that there is therefore no merit in this litigation.”