A new study from Dr Tom Freeman of the Addiction & Mental Health Group at the University of Bath suggests that some people’s genetic make-up could make them more prone to cannabis addiction.

However, when it comes to impairment caused by cannabis, a separate but related study from the same team, finds that cannabis strains containing more cannabidiol (CBD) result in lower impairment to brain function.

Publishing their results in the journal Addiction Biology, the team firstly wanted to investigate three different markers of genetic variation which had previously been implicated in cannabis addiction but to date had not all been studied together.

For their first study, 48 people took cannabis using a vaporiser, while the team conducted tests related to addiction predisposition. This included tests for: drug cue salience, which looked at how ‘attention grabbing’ cannabis-related images were versus more neutral ones; satiety, testing whether individuals still wanted more cannabis after consumption; and a measure for craving. Participants were also tested for the three genetic markers.

The researchers chose to focus on the specific cognitive mechanisms involved in addiction, rather than a general measure of cannabis dependency, to get a more detailed picture of how genetic markers affect the brain mechanisms that contribute to long-term drug dependency.

They found differences to drug cue salience and state satiety for all three genetic variants. One genotype in particular, regarding the Cannabinoid receptor 1 gene, was associated with people continuing to want more cannabis after having used it, and continuing to be more drawn to cannabis-related imagery while under the influence.

The team say this suggests that people with that genetic marker could be more prone to cannabis addiction, especially as THC - the psychoactive component in cannabis - binds to this receptor.

The second study which has important implications for doctors and users suggests that the more CBD in a given strain of cannabis, the lower the impairment to brain.

Published in the Journal of Psychopharmacology, the research is the first of its kind to use fMRI (functional magnetic resonance imaging) to gauge how different strains of cannabis impact brain function.

There is growing evidence that THC is implicated in addiction and cannabis-induced psychosis. CBD, on the other hand, is being researched for a range of potential therapeutic functions, whilst the interplay between THC and CBD is not yet well-known.

In the latest study, the researchers monitored brain activity at rest in 17 people after taking different strains of cannabis.

The two strains had equal levels of THC, but one of them also has high levels of CBD while the other strain, a high-strength cannabis commonly known as skunk, contained negligible levels of CBD. Both strains are comparable to the different strains of cannabis in common usage.

The researchers found that the low-CBD strain produced widespread reductions in connectivity in the brain’s salience network, while the high-CBD strain caused only minimal disruption, suggesting that the CBD counteracts some of THC’s harmful effects.

Their findings provide fresh insight into why CBD holds potential for medicinal uses.

Dr Tom Freeman explained: “Our findings have the potential to inform precision medicine targeting the rising clinical need for treatment of cannabis use disorders.

“We found that the presence of CBD in cannabis offset the effects of THC on connectivity within a large scale resting state network that toggles between internally driven thoughts and external behaviours. This is the first study to show how different strains of cannabis affect the brain during acute intoxication. These findings provide new insight into the mechanisms through which CBD may reduce the harmful effects of cannabis for addiction and mental health.”

The CBD study involved researchers at UCL, Invicro, King’s College London, Imperial College London, and the University of Bath and was supported by Drug Science, Channel 4 Television, and the Beckley Foundation.

Dr Freeman and colleagues led the recent clinical review into medicinal use of cannabis based products and cannabinoids published last month in the BMJ.