The trial of a new painkiller has gone drastically wrong in France, leaving one person brain dead and five others in a serious condition.

On Friday, one source apparently familiar with the situation initially said the drug was a cannabis-based drug. French Health Minister Marisol Touraine later denied this, however, and said the painkiller contained neither cannabis nor any substance derived from cannabis.

The medicine involved works by targeting the body's pain-controlling endocannabinoid system, which is also responsible for the human response to cannabis.

France's health ministry said that the six volunteers at the facility in Rennes, Brittany, had been in good health until taking the oral medication, which was manufactured by Portugal-based Bial lab and being tested in a Phase I trial at the Biotrial clinic in the northwestern French city.

Touraine said two investigations had been launched, including one by France's National Agency for Medicines and Health Products (ANSM).

The volunteers are all men aged 28 to 49, Touraine told a news conference. They started taking the drug on January 7. One person started feeling ill on Sunday and the other five afterwards.

In total, 90 people have taken part in the trial, taking some dosage of the drug, Touraine said, adding that others took a placebo.

Pierre-Gilles Edan, head of the neurology department at Rennes hospital, told reporters that three of the patients could suffer "irreversible" disability as a result of brain injuries.

The brain dead individual was admitted to hospital in Rennes on Monday. Other patients went in on Wednesday and Thursday. All trials on the drug have now been suspended and all volunteers who have taken part in the trial are being called back.

The health minister told reporters that she was still waiting to hear back from other volunteers who took part in the clinical trials in hospitals in the northwestern region of Brittany and in the district of Mayenne.

A spokeswoman for the European Medicines Agency in London said it did not have full details of the case but that it was monitoring the situation.

More than 1,700 clinical trials are authorized each year in France by ANSM, half of which test new drugs. Speaking to VICE News on Friday, a spokesperson for ANSM described today's incident as "an exceptional — in fact, very exceptional — case… given the severity of the patients' condition."

"To my knowledge, this case is a first in France," said Jean-Christophe Coubris, an attorney who specializes in cases involving drugs. Coubris told VICE News that: "Whatever contract these patients may have signed, they will be protected by French legislation in the case of proven misconduct."

The attorney such a case was "almost inconceivable" in 2016. "It seems absurd, since this was only Phase I, i.e. the first introduction [of the drug] into the human body," he said, adding that studies usually start with very low doses.

In the initial so-called Phase I stage of clinical testing, a drug is given to healthy volunteers to see how it is handled by the body and what is the right dose to give to patients.

Cases of early-stage clinical trials going badly wrong are rare but not unheard of. The last drug trial disaster in Europe occurred in 2006, when six healthy volunteers given an experimental drug in London ended up in intensive care.

One of them was described as looking like "the elephant man" after his head ballooned. Another lost his fingertips and toes.

In the initial so-called Phase I stage of clinical testing, a drug is given to healthy volunteers to see how it is handled by the body and what is the right dose to give to patients.