Some media reports in France claimed the drug was a cannabis-based painkiller and AFP quoted a source “close to the case” who said the drug contained cannabinoids – an ingredient found in cannabis plants.

However a spokesperson for France's health ministry has told The Local this information is false.

“This medication did not contain cannabis and was not a cannabis-based drug,” said Health Minister Marisol Touraine.

According to France's Minister of Health Marisol Touraine the trial has been called off after one person was left brain-dead and five others hospitalised after taking the drugs.

However some reports suggest the victim has been left in a coma, which would mean the brain damage may not be permanent. 

It is believed eight people were taking part in the trial, but of two of them had been given a placebo.

“A serious accident took place,” the minister said, adding the study had been halted and all volunteers taking part recalled.

“This trial was performed in a licensed private institution specializing in the conduct of clinical trials (…) in healthy volunteers. This accident caused the hospitalization of six of the volunteers at the University Hospital of Rennes. One of them in intensive care, is brain dead,” said the minister in a statement.

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The Paris prosecutor's office said an investigation had been opened by police as well as health authorities.

Touraine, who was informed of the accident on Thursday evening, was on her way to Rennes on Friday morning, where she is expected to hold a press conference along with a representative from the company Biotrial which was leading the trial.

The study was a phase one clinical trial, in which healthy volunteers take the medication to “evaluate the safety of its use, tolerance and pharmacological profile of the molecule”, the minister added in a statement.

Touraine gave no further details on the type of drug being trialed or what it would eventually be used for.

She simply said it was a medication “taken orally and in the process of being developed by a European laboratory”.

Medical trials typically have three phases to assess a new drug or device for safety and effectiveness.

Phase I entails a small group of volunteers, and focuses only on safety.

Phase II and Phase III are progressively larger trials to assess the drug's effectiveness, although safety remains paramount.

Touraine said she was determined to “shed light on” what happened.

The trial was being carried out by the private laboratory named Biotrial, that was accredited and approved by the Ministry of Health. 

The firm released a statement via Twitter in which it insisted that all the necessary rules were followed.

Biotrial is a French company that employs 300 people worldwide, including 200 in France. It also has labs in Paris and in London and New Jersey, from where it carries out “a large variety of early clinical studies,” according to its website.

On its website Biotrial boasts of having 25 years experience in clinical drug trials. 

Every year thousands of volunteers, often students looking to make extra money, take part in such clinical trials which are seen as safe.