One person is in a coma and five others critically ill after participating in a clinical trial in France . The Health Ministry has denied media claims the drug was a cannabis-based painkiller, the BBC reported. Biotrial, a company based in France, had reportedly been carrying out the trial at a clinic in northwest France.

The injured people are being treated at Rennes University Hospital, and the trial has since been suspended and other volunteers recalled. French Health Minister Marisol Touraine called it a "tragic accident" and pledged to get to the bottom of what went wrong while the prosecutor's office in Paris said it opened an investigation. Touraine was expected to travel to Rennes Friday.

The trial was a Phase I clinical trial, which typically means healthy volunteers are given the small doses of a medication to test its safety, not its efficacy. The botched trial had aimed to determine the "safety, tolerance and pharmaceutical properties of the molecule" for healthy people, the Independent reported.

Of the six people injured, one was fully brain dead and the others were in critical neurological condition. When the accident occurred remains unclear, with media reports saying the beginning of the week and the Health Ministry saying Thursday. The medication was an oral one, Touraine said, and the ministry said the testing had been carried out by a private company that was “specialized in carrying out clinical trials,” the Guardian reported.

French media reports said the drug was a cannabis-based painkiller, the Independent reported. 

Historically, studies have examined whether cannabinoid receptors (cannabinoids are compounds in a resin produced by marijuana) in various parts of the body have a role in relieving pain, and studies on animals have shown that cannabinoids potentially can prevent nerve problems. The idea that marijuana can help relieve pain has been one of the drivers of its legalization for medicinal use in numerous U.S. states, but actual studies testing the efficacy of cannabinoids on pain remain limited. Some research has indicated marijuana is more of a pain distracter than a pain reliever.