One person is brain-dead and five have been hospitalized after taking part in a clinical trial of an experimental drug at a hospital in Rennes, the French Ministry of Health said.
The affected volunteers, between the ages of 28 and 49, were taking part in a trial at a private hospital that specializes in clinical trials.
Among those hospitalized, three have irreversible brain damage, Rennes chief neurosurgeon Gilles Edan said at a press conference.
It is unclear what kind of drug was being tested but the minister of health, Marisol Touraine, told reporters it was an oral drug developed by a European lab. The drug, according to Touraine, affects the endocannabinoid system.
The lab has informed the national agency for drug safety - Agence Nationale de Sécurité du Médicament et des Produits de Santé (ANSM) - that it is suspending the trials. In addition, health authorities have recalled all 90 volunteers involved with this trial since July 2015. The agency will also inspect the location of the trial.
Touraine has asked the Inspector General of Social Affairs to lead an investigation into the circumstances around the trial.
The study was the first phase of a clinical trial in which healthy volunteers take the medication to "evaluate its safety."