The head and founder of France's Servier laboratories went on trial on Tuesday (May 21) accused of misleading patients and authorities about a diabetes pill 'Mediator' often prescribed for weight loss that officials blame for at least 500 deaths.

The case, one of France's biggest health scandals, has put authorities under scrutiny for allowing the sale of Mediator long after the medicine had been pulled in other European countries.

Mediator -- an anti-diabetic drug that was mostly prescribed by doctors as a weight-loss pill -- was sold to as many as 5 million people between 1976 and November 2009, when it was withdrawn, years after being pulled in Spain and Italy.

The president of a group of plaintiffs, Pierre Rinalduzzi, said the case did not solely target the ageing company director Jacques Servier.

The trial opened amid uncertainty as the defence and some civil parties have asked for the cancellation or delay of the trial.

Presented by Adam Justice