A man who was left brain-dead after taking part in a drug trial for an experimental painkiller based on a compound similar to cannabis died in France on Sunday, Rennes University hospital said in a statement.
French health authorities have said three of those still hospitalized face possible brain damage, and an investigation is underway into what French Health Minister Marisol Touraine called "an accident of exceptional gravity."
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 were given placebos. The six men who were hospitalized were the group that received the highest dose.
The trial began Jan. 7.
The hospital said it has contacted the other volunteers exposed to the new painkiller. Ten of those volunteers underwent medical exams Saturday but the hospital found no anomalies, it said.
It is 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.