One person is in a coma and five others are in critical condition after participating in a drug trial in France, the country's health ministry announced Friday. In a statement, the health ministry said a "serious accident" occurred at a private laboratory in the city of Rennes, and that all trials of the drug have been suspended there. French prosecutors have opened an investigation.

The ministry did not name the drug that produced it, saying only that it was "a drug taken orally being developed by a European laboratory." French media outlet iTélé reported this morning that the trial involved a cannabis-based painkiller, but at a press conference Friday afternoon, Health Minister Marisol Touraine said that the drug did not contain any cannabis or cannabis derivatives, adding that it acts upon cannabinoid receptors in the brain.

"This is unprecedented."

The drug was developed to treat neurodegenerative conditions, and was being tested by Biotrial, a laboratory based in Rennes. Biotrial's website includes a call for volunteers to participate in trials at Rennes and Newark, NJ, but the link to the Rennes volunteer page is currently broken. A Biotrial representative declined to comment when reached by phone Friday morning.

All six volunteers were men between the ages of 28 and 49, and were in good health prior to taking the oral medication at their homes, Touraine told reporters. Phase-1 testing of the drug began on January 7th and involved 90 people. The lab is contacting the other participants, and has suspended the trial following the incident.

The first of the six patients reported symptoms on Sunday night. One has been declared brain dead, and three others are at risk of suffering permanent handicaps, Pierre-Gilles Edan, head of neuroscience at the CHU Rennes hospital, said at Friday's press conference. In its statement, the health ministry said the trial aimed to evaluate the safety, tolerance, and pharmacological profile of the new drug. The ministry was first notified of the situation last night.

"I am not aware of any other comparable event," Touraine said. "This is unprecedented."

This article has been updated to include comments from Health Minister Marisol Touraine.