Alcohol, tobacco, and cannabis are three commonly used drugs, and they may be used independent of one another, in a combination of the two, or all three may even be used by an individual. Use, co-use, and tri-use are terms that can be used to describe these conditions. Previous research has found evidence that when the brains of users are compared to nonusers, their brains appear abnormal. Specifically, it appears that users tend to have a reduction or loss of a certain type of material that helps to make up our brain.

Our nervous system, consisting of our brain and a long cord that runs down our back, known as the spinal cord, is made of two types of material known as grey matter and white matter. Within our nervous system, we have individual functional units known as cells. The cells in the nervous system are rather unique. There are two types but here, we are focused on neurons. They consist of a spherical component (the cell body) and long strands that extend from it and send messages to other cells (axons). Grey matter is made up of the spherical components and appears to be the target of alcohol, tobacco, and cannabis use according to previous research. Specifically, their use tends to affect the outermost, wrinkled layer of our brain known as the cortex, and a few other brain structures found underneath the cortex, for example, our sensory switchboard, the thalamus, and part of our memory system, the hippocampus.

Previous studies mostly focused on the effects of single-use, and co-use on such structures. The most studied form of co-use is combined alcohol and tobacco use which appears to cause more changes in brain structure than alcohol use alone. To add to our understanding of the effects of these drugs on the grey matter within the brain, one study set out to compare the effects of alcohol use alone to alcohol and tobacco co-use, alcohol and cannabis co-use, and finally, alcohol, tobacco, and cannabis tri-use (Grodin et al., 2021). The participants of the sample collected were all determined to be heavy drinkers and fell into one of the four listed comparison groups. The study collected images of the participant’s brains by using an MRI, a machine that essentially uses magnets to capture images of a person’s brain structure on a computer.

The images revealed mixed results. Alcohol and tobacco co-users were found to have less grey matter than alcohol-only users in a specific region of the cortex; the area of the brain that sits just above your eyes, known as the orbitofrontal cortex. This means that the cell bodies of the brain cells have been reduced in number in this area, causing it to look smaller in the image. Alcohol and cannabis co-users, as well as the tri-users, did not appear to have any differences in brain structure when compared to the alcohol-only group. The lack of differences in grey matter for groups involving cannabis use could potentially be explained by the mixed results of previous cannabis use studies. The effects of cannabis use on brain structure are so far unclear. The findings of this study are, however, consistent with previous research in that alcohol and tobacco co-use causes more damage to the cell bodies of the neurons in our brain than alcohol use alone.

Reference:
Grodin, E., Burnette, E., Towns, B., Venegas, A., & Ray, L. (2021). Effect of alcohol, tobacco, and cannabis co-use on gray matter volume in heavy drinkers. Psychology of Addictive Behaviors, 35(6), 760–768. http://dx.doi.org.cbu.idm.oclc.org/10.1037/adb0000743