NANTERRE, France (AP) — The first French trial has begun over a diabetes drug that was also used to lose weight and is suspected in the deaths of at least 500 people.

The pharmaceutical group Servier is suspected of “aggravated deception” for hiding the fact that the drug known as Mediator contained an amphetamine called benfluorex — which was taken off the market in 2009 after being found to thicken heart valves.

However, another investigation is underway and lawyers for Servier were arguing Monday against holding the current trial claiming that the laboratory could be judged twice on the same grounds.

The nature of benfluorex was allegedly hidden to obtain approval for the drug, first marketed in 1976. So far, charges have been filed against seven people, including drugmaker chief Jacques Servier.