A naturally occurring hormone acts as spontaneous defence in the brain against the high caused by marijuana and could be useful in preventing addiction, researchers say.
French researchers studied lab rats and found that the steroid hormone pregnenolone reduced the activity of a particular brain molecule called the type-1 cannabinoid receptor (CB1).
The hormone, which was not previously believed to have any biological effect of its own, actually cancels out the "high" caused by THC, the psychoactive ingredient in marijuana, according to lead author Pier Vincenzo Piazza of the French Institute of Health and Medical Research (INSERM).
"These researchers weren't trying to be buzzkills," said the journal Science, in which the study appears.
"Their discovery could lead to new approaches to treating marijuana intoxication and addiction - and it may allow researchers to isolate the medicinal properties of cannabis while blocking its behavioural and somatic effects."
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About 147 million people globally - or about 2.5 per cent of the population - use cannabis, according to the World Health Organisation.
While cannabis products can alleviate symptoms of depression, glaucoma, spasms, and nausea associated with cancer and AIDS, they are also known to impair brain development, memory and lung function, and some say they can lead to addiction.
Researchers discovered the previously unknown role of pregnenolone when they administered high doses of cannabis to lab rats, on the order of three to 10 times more than the typical human marijuana smoker might be exposed to, Piazza said.
The high doses of cannabis raised the brain's level of pregnenolone, which blocked the harmful effects of THC on the brain.
