A court on Monday found pharma giant Servier guilty of manslaughter over hundreds of deaths caused by its diabetes and weight loss pill, in one of France's biggest health scandals.

The drug Mediator was on the market for 33 years and used by about five million people before being pulled in 2009 over fears it could cause serious heart problems -- more than a decade after such concerns had first been raised.

The company "weakened people's trust in the health system", the court's presiding judge Sylvie Daunis said as she pronounced the verdict.

"Although they knew about the risks for many years ... they never took the necessary measures", she said.

Instead the company "misled" consumers, she said, fining the company 2.7 million euros  for aggravated deceit, manslaughter and causing unintentional injury.

Servier's former deputy boss, Jean-Philippe Seta, was sentenced to a suspended jail sentence of four years.

Its powerful chairman, Jacques Servier, died in 2014.

France's medicines agency, meanwhile, was fined 303,000 euros for its delay in suspending the use of the drug.

In a damning verdict for the regulator the court convicted it of manslaughter and causing unintentional injury, saying it "seriously failed in its role as health watchdog".

Initially intended for overweight people with diabetes, Mediator was widely prescribed to healthy individuals as an appetite suppressant.

The first cases of heart disease linked to the drug were flagged in 1999, a decade before the drug was withdrawn.

Over 6,500 plaintiffs, including France's health insurance funds, are seeking one billion euros in damages.

Many of the victims who testified in court about the impact of the drug on their lives were women. 

"It was said that the drug was extraordinary. I lost ten kilos the first month," said one plaintiff, Stephanie, who took the drug for three years before being diagnosed with heart disease in 2009.

About 500 people are thought to have died as a result of the drug, though experts say it may eventually cause as many as 2,100 deaths.

Thousands of victims have already reached settlements with the company, totalling nearly 200 million euros, according to Servier.

The Mediator affair was the subject of the 2016 French film "150 Milligrams", about the work of lung specialist Irene Frachon who was instrumental in bringing the wrongdoing to light.

Servier and Seta claimed they did not know the drug was dangerous until 2009 when it was withdrawn. 

By then it had been outlawed in the United States, Spain and Italy.