A clinical trial of a new drug in France has left one person brain-dead and another five people in hospital, the health minister says.
The oral trial was being conducted by a private laboratory in the north-western city of Rennes, Marisol Touraine said.
The trial has been suspended and the firm is recalling the volunteers. It is unclear how many people are involved.
Media reports that the drug is a cannabis-based painkiller have been denied by the health ministry.
The Paris prosecutor’s office said an investigation had been opened.
The drug was taken in a licensed laboratory, the ministry said in a statement (in French).
Ms Touraine, who was heading for Rennes on Friday, pledged to “get to the bottom… of this tragic accident”.
The first people to fall ill were taken into hospital earlier this week, French media say.
The study was a Phase I clinical trial, in which healthy volunteers take the medication to evaluate the safety of its use, the ministry said.