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New research reveals how cannabis alters brain function

20 January 2009

Two recently published research papers have used functional MRI (fMRI) to show how the two main constituents of cannabis Tetrahydrocannabinol (THC) and Cannabidiol (CBD) act on the brain to modulate cognitive function and psychiatric  symptoms.

Cannabis is the world’s most widely used illicit drug and has a wide range of psychological and symptomatic effects.  In the short term cannabis can induce psychotic symptoms and anxiety, while regular use is associated with cognitive impairments and an increased risk of schizophrenia.  

Talking about the latest research published by the Institute of Psychiatry at King’s College London, into the effects of cannabis, Professor Philip McGuire one of the authors said: 'The Institute has been at the forefront of research into the adverse psychiatric effects of cannabis use.  These new findings further develop scientific understanding in this area by indicating how the two main psychoactive constituents of cannabis act on the brain to alter cognitive function and induce psychiatric symptoms.'

The studies were initiated by Philip McGuire and Zerrin Atakan from the Institute of Psychiatry at King’s, Jose Crippa from Ribeirão Preto, Brazil and Rocio Martin-Santos in Barcelona, Spain.   They and a team of researchers at the Institute used functional magnetic resonance imaging and behavioural measures to assess the impact on brain function in healthy male volunteers.  Each subject was scanned on three occasions at monthly intervals, with each scan preceded by the administration of either THC, CBD or a placebo.

In the first paper published in Biological Psychiatry in December 2008, 'Neural Basis of Δ-9-Tetrahydrocannabinol and Cannabidiol: Effects During Response Inhibition' the researchers considered the effects of THC and CBD on brain function during a Go/No Go task which requires subjects to over-ride a regular button pressing response.  They found that THC reduced activation in the part of the prefrontal cortex that is normally critical for this ‘response inhibition’ process.  Please refer to the journal for a full copy of the paper. (Biological Psychiatry 64 (11), pp. 966-973) doi:10.1016/j.biopsych.2008.05.011)

In the second paper published in the Archives of General Psychiatry (12 January 2009) 'Distinct Effects of _9-Tetrahydrocannabinol and Cannabidiol on Neural Activation During Emotional Processing'  the researchers investigated the neurophysiological basis of the effects of cannabis on anxiety, using faces that had fearful expressions.  Normally viewing fearful faces provokes anxiety, activates the amygdala, and increases skin conductance (a measure of autonomic arounsal).  Administration of CBD reduced the response of the amygdale to fearful faces, and this effect was correlated with its effect on skin conductance.  Please refer to the Archives of General Psychiatry, January 2009 issues for full copies of this paper.  (Arch Gen Psychiatry, 2009;66 (1): 95-105.)

Professor Philip McGuire concludes, 'These studies show that THC and CBD have distinct effects on brain function in humans, and these may underlie their correspondingly different effects on cognition and psychiatric symptoms.  Determining how the constituents of cannabis act on the brain is fundamental to understanding the role of cannabis use in the aetiology of psychiatric disorders.'

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