Biotrial has carried out thousands of trials since it was set up in 1989

A man left brain-dead after an experimental drug trial in France has died, local media report.

The man was one of several volunteers taken ill in the city of Rennes.

On Friday, the chief neuroscientist at the hospital, Gilles Edan, said there was a risk that three of six volunteers being treated could have permanent brain damage.

Reports that the drug was a cannabis-based painkiller have been denied by the French health ministry.

All those who volunteered for the trial have undergone hospital tests, and the Paris prosecutor's office has opened an investigation.

The 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.

Mr 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.

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Clinical trials

Trials typically have three phases to assess a new medicine for safety and effectiveness

• Phase I tests for safety. A small number of people, sometimes healthy, and sometimes with a medical condition, are given a tiny dose of the drug under careful supervision, not to test if the drug works, but in order to check for any side effects
• Phase II sees the drug given to people who have a medical condition to see if it does indeed help them
• Phase III trials are only for medicines or devices that have already passed the first two stages, and involve them being compared to existing treatments or a placebo. The trials often last a year or more, involving several thousand patients

Has drug trial safety improved?