One man is in a coma and brain dead while five others are seriously ill after a medical trial in France went wrong.

The trial involved a drug manufactured by Portuguese company Bial.

90 people were given the experimental drug in various doses, and there is no known antidote.

The drug was initially reported to have been a cannabis-based painkiller, but those reports have been denied by the health ministry.

The study was a Phase I clinical trial, where healthy volunteers take medication to evaluate its safety for wider use.

Medical lawyer Philippe Courtois told French media: "This is the most serious case I have come across".

A formal investigation has been opened in Paris.