Strong cannabis found to hinder communication between brain's left and right hemispheres

Smoking skunk-like cannabis wreaks havoc on a part of the brain that is responsible for communication between the two hemispheres of the brain, a new study claims. Researchers from King's College London and Sapienza University of Rome found that skunk smokers could be more susceptible to mental health conditions such psychosis, because of changes in the way the brain's hemispheres communicated.

Skunk is a particularly strong strain of cannabis, and the most commonly smoked in the UK. The researchers set out to find the impact of cannabis potency on the brain – previous research has shown that marijuana products high in THC showed that the main ingredient of marijuana can induce psychotic symptoms.

Dr Paola Dazzan, Reader in Neurobiology of Psychosis from the Institute of Psychiatry, Psychology and Neuroscience (IoPPN) at King's College London, and senior researcher on the study, said: "We found that frequent use of high-potency cannabis significantly affects the structure of white matter fibres in the brain, whether you have psychosis or not. This reflects a sliding scale where the more cannabis you smoke and the higher the potency, the worse the damage will be."

Diffusion tensor imaging (DTI), a magnetic resonance imaging (MRI) technique, was used to analyse the amount of white matter in the brain of 56 participants who had experienced a first episode of psychosis, as well as 43 healthy patients, according to the study published in the journal Psychological Medicine. They examined the corpus callosum – the largest white matter structure in the brain – which is the main component for communication of the hemispheres and is also plentiful in cannabinoid receptors.

White matter is essential to the brain as it contains an abundance of nerve cell projections, which acts as a link between different parts of the brain – meaning that each part of the brain can operate in conjunction with other parts. In its research, the team found that high potency cannabis was correlated with damage of white matter structure.

Dr Tiago Reis Marques, a senior research fellow from the IoPPN at King's College London, said: "This white matter damage was significantly greater among heavy users of high potency cannabis than in occasional or low potency users, and was also independent of the presence of a psychotic disorder."

Dazzan added: "There is an urgent need to educate health professionals, the public and policymakers about the risks involved with cannabis use. As we have suggested previously, when assessing cannabis use it is extremely important to gather information on how often and what type of cannabis is being used. These details can help quantify the risk of mental health problems and increase awareness on the type of damage these substances can do to the brain."