A naturally occurring hormone can be used to extinguish the "high" produced by cannabis, research has shown.
The discovery could lead to new approaches to treating cannabis intoxication and dependence. It may also assist in the use of cannabis for medicinal purposes while blocking its psychoactive effects.
Researchers found that the steroid hormone pregnenolone reduces the brain's sensitivity to THC, the chief high-inducing compound in cannabis.
Scientists led by Dr Monique Vallee, from the University of Bordeaux in France, studied mice and rats to see how recreational drugs such as cocaine, alcohol and cannabis affected the production of steroids in the brain involved in nerve function.
They found that THC triggered a dramatic spike in pregnenolone through activation of the cannabinoid receptor (CB-1), a molecule that facilitates cannabis stimulation.
This in turn had a "negative feedback" effect leading to a blunting of THC activity.
The findings, published in the journal Science, follow the decision to legalise the recreational use of cannabis in the US state of Colorado.
The scientists wrote: "This new understanding of the role of pregnenolone has the potential to generate new therapies for the treatment of cannabis dependence."