King’s College Study Suggests High-Potency Cannabis Can Damage the Brain

In March of 2016 researchers at King’s College published an open access article in Psychological Medicine that suggests pot smokers may suffer microstructural changes in an important part of the brain called the corpus callosum (CC), a structure that connects the two hemispheres.

At the beginning of the publication, the authors remark that the use of cannabis with higher levels of THC has been associated with a greater risk for earlier onset of psychosis. This is only true in those who have a genetic susceptibility to psychosis, NOT in otherwise healthy patients.

Here, they investigated whether cannabis potency and pattern of use are associated with changes in corpus callosum (CC) microstructural organization, in patients with first-episode psychosis (FEP) and individuals without psychosis, cannabis users and non-users.

They have demonstrated that higher potency cannabis does cause changes in the brain, not only in those predisposed to psychosis, but also in those without psychosis.

Some authors have proposed that the THC component of cannabis may have a neurotoxic effect on the brain (Gilman et al.2014), while the CBD component has been proposed to be actually neuroprotective (Pertwee, 2008). While long-term use of cannabis has been associated with alterations in brain function and morphology the effect of potency has never been explored.

The study’s main author Dr. Rigucci:

As the CC has a fundamental role in inter-hemispheric connectivity, it is not surprising that this structure has been widely implicated in both psychosis and cannabis-associated behaviours (Arnone et al.2006; Walterfang et al.2008).

Interestingly, changes in CC integrity have often been observed in individuals without psychosis but with a history of heavy and long-term cannabis use. Based on this observation there doesn’t appear to be a consistent relationship between altered CC architecture and abnormal behavior.

Corpus Collpsum


Fig 1: Corpus callosum tract: whole (a) and segmented (b). Regions of interest as defined according to Witelson ( 1989) subdivisions.

The conclusions of the study:

Our main finding, which is in line with our main hypothesis, is that frequent use of high-potency cannabis is significantly associated with altered callosal microstructural integrity. Furthermore, our results suggest that this particularly occurs in the most posterior part of the CC, including the splenium and the posterior mid-body. Interestingly, these alterations were similar in users with and without a psychotic disorder.

The theory is that there exists a rich deposit of CB1 receptors on the CC, and that during development, high-THC cannabis affects the maturation of the CC due to ‘down regulation’ of CB1 receptors. This in turn may cause the growth of neurons in the CC to die off. This was particularly seen in the splenium (see figure 1 b).

The authors also reported:

We were somewhat surprised to see that differences in callosal integrity in relation to cannabis potency were larger in the individuals without psychosis than in the [psychotic] patients….Our data go further than previous evidence and suggest that cannabis potency and frequency affect the CC in individuals with and without psychosis, and possibly reflect a subtle and general effect rather than altered neuronal integrity.

Lastly, the study’s authors conclude:

This study provides the first report that white matter (WM) disarray is greater among heavy users of high-potency cannabis, than in occasional or low-potency users, and that this is independent of the presence of a psychotic disorder. Unfortunately, high-potency cannabis is replacing traditional herbal cannabis preparations in many European countries. Raising awareness about the risks of high-potency cannabis abuse seems therefore crucial.

As yo can see from above, they found changes in WM of which the CC is one such structure. However, there seems to be no clinical correlation with WM changes in high-potency marijuana users and the development of either schizophrenia or any other psychotic disorder.

In the final analysis this study exaggerates the microstructural changes in the CC suggesting that these changes can cause an increase in neurobehavioral effects. Which, of course, the study does not demonstrate. In other words, although there seem to be subtle changes in the white matter within the brains of high-potency cannabis users it does not clinically appear to increase the risk for psychiatric disorders.

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