One person has been left brain dead and five people hospitalised after a "serious accident" during a drugs trial in France.
The six people were taking part in a trial of oral medication, in the northwestern city of Rennes, Health Minister Marisol Touraine said.
Agence France cited a source who said the drug was a painkiller containing cannabinoids, an active ingredient found in cannabis plants.
But The Local reported this was not the case.
Touraine said the study had been stopped and all other volunteers recalled. She added she would "shed light" on what happened and prosecutors have opened an investigation.
She added: "This trial was performed in a licensed private institution specialising in the conduct of clinical trials in healthy volunteers.
"This accident caused the hospitalisation of six of the volunteers at the University Hospital of Rennes. One of them in intensive care, is brain dead."
The accident was during a Phase I clinical trial at a lab in Rennes that specialises in them.
"Marisol Touraine wants to express her solidarity and deep determination to get to the bottom of what happened and establish responsibility for this tragic accident," the French Health Ministry said in a statement.
Mishaps are relatively rare, but in 2006 six men were hospitalised in London after taking part in a clinical trial into a drug developed to fight auto-immune disease and leukaemia.Suggest a correction