One clinical-trial volunteer is brain dead and five others have been hospitalized, French officials said Friday.
The country's Ministry of Health said an investigation has been launched into the incident at the privately-licensed laboratory in Rennes specializing in conducting clinical trials.
The lab informed officials overnight about the accident and subsequent interruption of the trial, the ministry said in a statement. All volunteers participating have been recalled.
French Health Minister Marisol Touraine was en route to Rennes on Friday and pledged to shed light on the circumstances of the tragedy, the statement added.
It did not name the lab, saying only that the accident affected a Phase 1 trial of an oral drug.
France-based Biotrial later confirmed that "serious adverse events" related to a test drug had occurred "in some subjects" during a study for a sponsor, saying in a statement the company was in "close and regular contact" with French authorities.
"The trial has been conducted in full compliance with the international regulations," the company said. "Biotrial's procedures were followed at every stage of the trial, in particular the emergency procedures for the transfer of subjects to the hospital."
Biotrial did not give any further details on the drug in testing or other trial volunteers.