In collaboration with Dr. Paul Morrison at the Institute of Psychiatry the Beckley Foundation is using EEG to study the differing effects of the constituents of cannabis, THC and CBD, on brain functioning. Our work so far has shown that THC produces certain neural responses which are similar to those observed in some types of mental illness, which may be the physiological basis of cannabis psychosis.
THC vs CBD
Cannabis is a complicated substance with over 400 constituent chemicals. The majority of research investigating the effects of cannabis has focused on D9-tetrahydrocannabinol (THC), which accounts for the main psychoactive effects associated with cannabis. THC has been shown to elevate levels of anxiety and produces ‘psychotic’ symptoms in 40-50% of healthy individuals (D’Souza et al., 2004).
In stark contrast, another constituent of herbal cannabis, Cannabidiol (CBD), appears to have an anti-psychotic profile, suggesting that it might actually be an effective medical treatment in many psychiatric conditions.
Content of Cannabis
Over the last 10 years the levels of THC has continued to increase in modern forms of street cannabis called “skunk”. This is largely due to advancements in cultivation techniques such as hydroponics, cloning, high-intensity artificial lighting and the selective breeding of high potency strains of skunk, all of which have made it possible to grow strains of skunk with ever increasing levels of THC. What is less well known is that a side-effect of these approaches has caused CBD, to be nearly eliminated from the plant.
Accumulating evidence suggests that THC and CBD act on the same physiological systems in a diametrically opposed fashion. This might explain why CBD has anti-psychotic properties, whereas THC has been associated with the induction of acute psychosis (Morrison et al. 2009). Using electroencephalography (EEG) we recently investigated the neural mechanisms by which THC causes its effects (Morrison et al., 2010). We tested the hypothesis that THC psychopathology is related to changes in EEG power or the coherence between differing areas of the brain. The results revealed that the pro-psychotic effects of THC might be related to impaired network dynamics with impaired communication between the right and left frontal lobes, which may be the physiological basis of cannabis psychosis.
Recently we compared the effects of a mixture of synthetic THC and CBD, (to mimic traditional cannabis) with THC on its own (to mimic skunk). The aim was to find out if CBD offered protection against the psychotic effects of THC. We found that overall, volunteers were rated as being significantly less psychotic after being given THC and CBD compared to THC on its own (Bhattacharyya et al., 2010). The implication of this study is that the presence of CBD in cannabis counteracts THC’s tendency to trigger transient psychosis.
Our findings suggests that the risk to cannabis users of experiencing an acute adverse psychological reaction has and will continue to increase as forms of street cannabis become ever more potent, while continuing to diminish CBD content.
Therapeutic Potential of CBD
CBD exhibits an impressive plethora of therapeutic uses, including anticonvulsive, sedative, hypnotic, antipsychotic, anti-inflammatory and neuroprotective properties. CBD is well tolerated in humans, with a profile of very low toxicity, and is devoid of psychoactive and cognitive effects.
To investigate the potential therapeutic applications of CBD in treating anxiety disorders we are carrying out two further studies at the Institute of Psychiatry. This study will use a virtual reality scenario to place participants in a stressful situation and test if CBD reduces anxiety in those vulnerable to such mental states.