A man who was left brain-dead during a drugs trial in France has died, while five others remain in hospital with grave fears for their recovery.

The Rennes University Hospital announced the death in a statement on Monday (AEDT), but did not identify the patient, who had already been brain dead.

According to the statement, five other volunteers hospitalised one week ago when the drugs trial went wrong, were “in a stable condition”.

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The drug, based on a natural brain compound similar to the active ingredient in marijuana, was given orally to healthy volunteers as part of a Phase 1 trial by Biotrial, a drug evaluation company based in Rennes, on behalf of the Portuguese pharmaceutical company Bial.

A total of 108 volunteers took part in the trial, 90 of whom received the drug at varying doses, while the rest of the people were given placebos. (The drug was formerly thought to contain a compound similar to cannabis. A representative for the company has denied this).

The six men aged between 28 and 49 who were hospitalised were the group which received the highest dose of the test drug.

The hospital’s head of the neurology Pierre-Gilles Edan said that three out of the remaining five surviving men were suffering a “handicap that could be irreversible” and that one of the men had neurological issues, the ABC reported.

French Health Minister Marisol Touraine called the incident “an accident of exceptional gravity”.

The trial, which began January 7, involved 90 healthy volunteers who were given the experimental drug in varying doses at different times.

The hospital said it had contacted the 84 other volunteers exposed to the new painkiller.

Ten of those volunteers underwent medical exams on Saturday but the hospital found no anomalies, the hospital statement said.

It said another five people in the trial would have medical exams closer to their homes.

In addition to treating pain, the drug was intended to ease mood and anxiety troubles as well as motor problems linked to neurodegenerative illnesses by acting on the endocannabinoid system.

In this system, natural brain compounds act on specific receptors to exert their effects.
It’s rare for volunteers to fall seriously ill during Phase 1 trials, which study safe usage, side effects and other measures on healthy volunteers, rather than drug effectiveness.

In a statement released by Bial, it said they followed “international best practice” while producing the drug and they were “co-operating” following the hospitalisation of its volunteers.

“Our principal concern, at the moment, is taking care of participants in the trial,” Bial said in a statement.

– with AAP