A major trial against one of France’s biggest pharmaceutical companies over a weight-loss drug suspected of causing up to 2,000 deaths is getting underway in Paris.

The landmark trial involves more than 4,000 plaintiffs accusing  Servier Laboratoires and the French medicines watchdog of involuntary manslaughter a deceit.

The lab is accused of covering up the killer side-effects of a widely-prescribed weight-loss drug named Mediator.

The regulator meanwhile is accused of failing to act to prevent patient deaths.

The amphetamine-derived drug was marketed to overweight diabetics but was often prescribed as a hunger suppressant to people attempting to lose weight.

As many as 5 million people were prescribed the drug between 1976 and 2009 – despite claims that it caused heart and pulmonary failures.

A 2010 found that the drug was suspected to have caused between 1,000 and 2,000 deaths – while the French health ministry found that at least 500 died from exposure to its active ingredient.

It is believed that thousands more are living with debilitating heart and lung problems after taking it.

It was only taken off the shelves in 2009 and court documents accuse Servier of knowingly concealing its true characteristics and suppressing unfavourable medical studies.

The firm has claimed it was not aware of the risks until 2009.

The drug was never licensed for sale in Ireland.

The trial is expected to last six months.