A King’s College London trial has demonstrated cannabidiol has anti-psychotic properties – although the way in which this is achieved remains a ‘mystery’, say researchers.

“The mainstay of current treatment for people with psychosis are drugs that were first discovered in the 1950s and unfortunately do not work for everyone,” says Dr Sagnik Bhattacharyya, from the Institute of Psychiatry, Psychology and Neuroscience.

“Our results have started unravelling the brain mechanisms of a new drug that works in a completely different way to traditional anti-psychotics.”

The researchers studied a group of 33 young people who had not yet been diagnosed with psychosis but who were experiencing distressing psychotic symptoms, along with 19 healthy controls.

A single dose of cannabidiol was given to 16 participants while the other 17 received a placebo.

All participants were studied in an MRI scanner while performing a memory task which engages three regions of the brain known to be involved in psychosis. As expected, the brain activity in the participants at risk of psychosis was abnormal compared to the healthy participants.

However, among those who had cannabidiol, the abnormal brain activity was less severe than for those who received a placebo, suggesting cannabidiol can help re-adjust brain activity to normal levels. The influence of cannabidiol on these three brain regions could underlie its therapeutic effects on psychotic symptoms.

Intriguingly, previous research from King’s College London shows cannabidiol appears to work in opposition to tetrahydrocannabinol (THC); the ingredient in cannabis responsible for getting users high which has been strongly linked to the development of psychosis.

THC can be thought of as mimicking some of the effects of psychosis, while cannabidiol has broadly opposite neurological and behavioural effects.

Dr Bhattacharyya and colleagues at IoPPN are now launching the first large scale, multi-centre trial to investigate whether cannabidiol can be used to treat young people at high risk of developing psychosis. The trial is supported by a £1.85m grant from an NIHR and MRC partnership. Some estimates suggest that in England alone, over 15,000 people present with early symptoms of psychosis every year.

“There is an urgent need for a safe treatment for young people at risk of psychosis,” says Dr Bhattacharyya.

“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.”

Meanwhile further research estimates that around one in 10 new cases of psychosis may be associated with strong cannabis.

In London and Amsterdam, where most of the cannabis which is sold is very strong, the risk could be much more, say researchers in The Lancet Psychiatry. Lead researcher and psychiatrist Dr Marta Di Forti said: “If you decide to use high potency cannabis bear in mind there is this potential risk.”

Dr Adrian James from the Royal College of Psychiatrists said:

“This is a good quality study and the results need to be taken seriously.”

Doctors are concerned about the growing use of high potency cannabis that contains lots of the ingredient THC – the one that gives the high. Skunk-like cannabis with a THC content of 14% now makes up 94% of the drug sold on the streets of London, according to experts