Cannabis and the Corpus Callosum

Consumption of legal marijuana and cannabis-containing products is on the rise in the United States, due to new laws allowing medical and recreational use in several states. Medicinal use of marijuana also appears to be increasing in Europe. With more marijuana and cannabis use, as well as better control of the active ingredients found in marijuana, people may want to have a greater understanding of how much cannabis they can safely use. Psychiatrists may also want to advise their patients who use recreational or medicinal cannabis about how much is too much, or whether any use is advisable.

Some researchers propose that the use of cannabis can cause psychosis.¹ A research group based in Italy and the UK conducted a recent study looking at the association between high potency cannabis as well as frequency of use and possible damage to the corpus callosum.² The corpus callosum is the large white matter tract connecting the two cerebral hemispheres. They also examined whether there is a relationship between white matter damage, cannabis use, and psychosis. The scientists used a brain-imaging technique called diffusion tensor imaging tractography to examine the corpus callosum in people with first episode psychosis who did or did not use cannabis compared to cannabis users with no history of psychosis.

The study subjects included a total of 56 people with first episode psychosis, of which 37 were cannabis users, and compared them to 43 cannabis users without any history of psychosis. All of the study subjects completed a survey that assessed whether or not they used cannabis, how often they used cannabis, and what kind of cannabis they used. This included questions about low-potency, defined as “hash-like,” and high potency, defined as “skunk-like.” According to the researchers, “skunk-like” cannabis is known to contain higher content of r Δ9-tetrahydrocannabinol, the active ingredient found in marijuana.

To measure corpus callosum damage, they looked at a property known as mean diffusivity. This is a way to determine the extent of existing white matter lesions in the brain.

Overall, the investigators found that those individuals who used higher potency cannabis had more white matter lesions in their corpus callosum when compared to users of the less potent forms of cannabis. Daily use was also associated with a corresponding increase in white matter lesions, as measured by mean diffusivity. The most posterior part of the corpus callosum showed the greatest effects. Surprisingly, these changes were similar in cannabis users regardless of whether or not they had a psychotic disorder. The researchers did not find an association between cannabis potency and psychosis, or frequency of use and psychosis.

Overall, the study authors concluded that “Frequent use of high-potency cannabis is associated with disturbed callosal microstructural organization in individuals with and without psychosis. Since high-potency preparations are now replacing traditional herbal drugs in many European countries, raising awareness about the risks of high-potency cannabis is crucial.”

The study results suggest that cannabis use may have detrimental effects on the brain, and in particular the corpus callosum. It seems unlikely, however, that psychosis is related to corpus callosum damage in these individuals. Further studies will hopefully focus on possible effects of cannabis on causing psychosis, possibly due to an impact on different brain areas. In addition, it would be of interest to understand what physiological effects other than psychosis may be caused by damage to the corpus callosum in cannabis users.

References:

1. Di Forti M, et al. Daily use, especially of high-potency cannabis, drives the earlier onset of psychosis in cannabis users. Schizophr Bull. 2014 Nov;40(6):1509-1517.

2. Rigucci S, et al. Effect of high-potency cannabis on corpus callosum microstructure. Psychol Med. 2015 Nov 27:1-14. [Epub ahead of print]