According to the French Government the Phase I study was being conducted by Biotrial in Rennes in the Northwest of the country.
The Government said the research was halted after six* serious adverse events occurred.
It also confirmed earlier reports that one subject is in a coma after the study and that he has has been declared brain dead -"est en état de mort cérébrale." The most recent updates state this patient has been declared "clinically dead."
According to the statement all injured volunteers are being cared for at the Centre Hospitalier Universitaire de Rennes (ou CHU de Rennes). The health condition of four of the patients is being described as "disturbing."
AFP reported that the drug being trialed is a cannabis-based pain medication being developed by Portuguese pharmaceutical company Bial. However, according to a BBC report, this has been denied by the French health ministry.
Bial did not respond to a request for comment.
Biotrial told this publication it will stream a press conference on its website at 14h30 CET.
A statement on the French contract research organisation's (CRO) website and Twitter now reads:
"During a FIM study which was being conducted for a sponsor, serious adverse events related to the test drug have occurred in some subjects at our CPU. The trial has been conducted in full compliance with the international regulations and Biotrial’s procedures were followed at every stage throughout the trial, in particular the emergency procedures for the transfer of subjects to the hospital.
"We are in close and regular contact with the Health Authorities and Ministry in France. The priority at Biotrial remains the safety of our subjects. We are very grateful for the support we have been receiving from our clients and partners today."
*French authorities have since confirmed that one of the five men showed no symptoms and was hospitalised as a precaution.