Once upon a time you'd mostly hear the likes of Cheech and Chong singing the praises of marijuana, but nowadays doctors and scientists are joining in. Compounds like cannabidiol (CBD) are of particular interest, since they've been found to impart benefits to the brain without the negative "stoned" side-effects. Now, researchers at King's College London have shown that CBD could help reset the brain abnormalities found in people suffering from psychosis.

Of all the cannabinoids that marijuana contains, THC is the most (in)famous. As the principal psychoactive compound, this is the stuff that's largely responsible for hallucinations, the feeling of getting high, and the reduced ability to distinguish between what's real and what's not.

But CBD could be the yin to THC's yang. Recent studies have found that its neurological and behavioral effects on people are almost the opposite, with evidence suggesting it can calm anxiety and relieve pain. Recently it even gained FDA approval as a treatment to reduce seizures in children with a rare form of epilepsy.

Since psychosis has a similar symptom list as THC – specifically the trouble in figuring out what's real – scientists have been studying CBD as a possible anti-psychotic drug. Results so far are promising, although the exact mechanism behind it is still unknown.

To investigate further, the King's College researchers tested cannabidiol on a group of young people who were beginning to show psychotic symptoms. Of the 33 test subjects, 16 received a single dose of CBD while the remaining 17 had a placebo, and these were compared to a control group of 19 others.

After their dose, the participants then performed a memory task specifically designed to involve three brain regions that play a part in psychosis. This was done inside an MRI scanner, to monitor brain activity. The results showed that abnormal brain activity was less severe in patients who received cannabidiol compared to those who had a placebo.

Of course, that's a pretty small test group, but the results are interesting enough that the King's College team is now planning to launch a large-scale trial into the possible anti-psychotic benefits of cannabidiol.

"There is an urgent need for a safe treatment for young people at risk of psychosis," says Sagnik Bhattacharyya, an author on the study. "One of the main advantages of cannabidiol is that it is safe and seems to be very well tolerated, making it in some ways an ideal treatment. If successful, this trial will provide definitive proof of cannabidiol's role as an antipsychotic treatment and pave the way for use in the clinic."

The research was published in the journal JAMA Psychiatry.

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