An experimental drug trial took life of a participant in France and sent five others to hospital in city of Rennes. French prosecutors have started a probe into the controversial case, which has raised questions over drug testing on healthy humans.

The unusual case is linked to a Portuguese pharmaceutical company which was conducting trials on its drug, Bial. The company has admitted that the man who has lost his life and five others hospitalized were part of its drug test. The company will work with health authorities to understand what caused this ill-fated situation during the trial, it said.

Western France’s Rennes University Hospital confirmed the death of brain-dead participant, but didn’t reveal his identify. The university announced that the drug trial, which began on January 7, has killed the person who had been in brain death state.

The brain dead participant was one of the six male persons who were taken to hospital last week. All of them were part of a drug test of Bial drug. As per French health authorities, three other participants who are currently in the hospital could face the brain damage condition.

The Paris prosecutor’s office announced in a statement that the investigation has begun after the recent death to include potential manslaughter charges. The trial by the Portuguese pharmaceutical company involved about 90 healthy participants who received the company’s experimental drug with different doses at different times.

As per a statement by the hospital, “We have contacted the 84 other volunteers exposed to the new painkiller. Ten of those volunteers underwent medical exams Saturday, but the hospital found no anomalies. Five will have medical exams closer to their homes”.

The controversial drug was also intended to ease mood and anxiety troubles.