A man left brain-dead after an experimental drug trial in France has died, local media report.He was one of six people being treated in hospital in the city of Rennes, reports BBC.The other five remain in a stable condition, the hospital said, four had "neurological problems", the fifth had no symptoms.Reports that the drug was a cannabis-based painkiller have been denied by the French health ministry. The Paris prosecutor has opened an investigationThe trial, which involved taking the drug orally and has now been suspended, was conducted by a private laboratory in Rennes.Ninety volunteers took the drug, manufactured by the Portuguese company Bial.All have undergone hospital tests.On Friday, the chief neuroscientist at the hospital, Gilles Edan, said there was no known antidote to the drug.The trial was conducted by Biotrial, a French-based company with an international reputation which has carried out thousands of trials since it was set up in 1989.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.Before any new medicine can be given to patients, detailed information about how it works and how safe it is must be collected.Clinical trials are the key to getting that data - and without volunteers to take part in the trials, there would be no new treatments for serious diseases such as cancer, multiple sclerosis and arthritis.New EU regulations to speed up clinical drug trials and streamline testing procedures across the 28-nation bloc are due to take effect in 2018.