Does Recreational Cannabis Change the Brain in Young People?

Yesterday a paper was published online in the Journal of Neuroscience which showed that even recreational cannabis smoking may affect the shape and size of certain regions of the brain. Of course this study got widespread attention in the media and I’ve seen headlines raging from the conservative “Casual marijuana use linked with brain abnormalities” right up to the scare-mongering headlines which attract readers such as “Casual marijuana may damage your brain”… Nowhere in this study did the authors even mention the word ‘damage’. It’s very likely that the latter journalists didn’t even read the paper. Lucky for you, I did!

This study carried out by a team based in the USA, looked at the effects of recreational cannabis use compared to controls (people with no cannabis use in the past year and less than five times in their lives) in forty young adults aged 18-25 years – probably college students who received a bit of cash to have their brains imaged. The people in the recreational cannabis group were those who smoked at least once per week but weren’t deemed to be dependent based on standard clinical questions to assess dependency.  So far so good.

What this study showed is that there were differences in the size and shape of certain brain areas in recreational cannabis users compared to the control group.  These regions were the amygdala and the nucleus accumbens, both regions have been shown to be important for addiction and reward in the brain.

cannabis change the brain - HeadStuff.org

This figure taken from the paper (Gilman et al. 2014) shows the brain scans and 3D reconstructions of the brain regions involved. On the top left you can a brain scan highlighting the amygdala in both hemispheres of the brain, notice there is no difference in size. 3D reconstruction (top right) shows a difference in shape between right and left amygdala. On the bottom left you can see a brain scan highlighting another brain region the nucleus accumbens, notice the difference in size between left and right. Again looking at the 3D reconstruction (bottom right) we can see that there is also a difference in shape, with abnormalities in the left nucleus accumbens.

And here I could stop this piece and have told you all the information that there is in the study.

But of course I will continue and do my best to give you a non-exaggerated view of what this actually means. This study was very well performed with appropriate, non-biased analysis of brain images, the researchers were blind as to who was in each group. But it seems to me like they were on a fishing expedition of sorts. They took two groups of people and scanned many different brain areas hoping to find a difference in size or shape of brain regions. That’s not to say their findings are not interesting, similar results have been shown in animal models whereby structural changes in these brain areas have occurred when rats have been given drugs such as cannabis… it is worth mentioning that they have also seen similar effects for nicotine and alcohol addiction.

So are these changes observed in specific brain regions really due to recreational cannabis use? Or could we find similar changes for recreational cigarette smoking or alcohol consumption? I think it’s possible that what these researchers have found could be simply due to recreational drug use and not specifically to cannabis. Of course the researchers are aware of this issue and have done their best to control for these issues, with subject reporting their cigarette and alcohol consumption so that we could try to correct for these differences. I just hope these students are telling the truth when reporting this information. Looking closely at the data in the paper (you can too by clicking on the link at the beginning of the article) the cannabis users indeed drink more alcohol than the control group. There is no statistically significant difference, but it is borderline (for those who know their statistics the p value is exactly 0.05, any lower and it would have been significant).

This study is  simply a correlation between brain structure, size and shape and cannabis use. If indeed it proves to be true, then it’s a good start but what would be more interesting is the “how?”, “why?” and “so what?”. Here, I am asking a lot. Science doesn’t normally advance in huge leaps, its more baby steps. So I’m sure that this paper will lead to further research investigating this phenomenon and we will be able to understand if these changes are of any consequence for the recreational cannabis user. For now we just don’t know.

Irish cannabinoid expert, Dr. Eric Downer, who runs his own lab in University College Cork commented on this paper telling HeadStuff, “Researchers have used various methods to determine whether cannabis consumption results in brain atrophy or morphometric changes in adult subjects, and close examination of the literature indicates overall contradictory results on the effects of cannabis consumption on brain composition in adults. What is clear is that the components in cannabis have hugely diverse effects on brain function, disrupting neurotransmitter, neuroimmune and endogenous cannabinoid systems, which certainly contribute to the behavioural effects of recreational use”

So should recreational cannabis users worry about this new study?

Not really. Let’s take their word and say cannabis really does change your brain. Well so do a lot of things like drugs, disease and even learning. Reading this article has probably in some way changed your brain, the change is probably too small to measure but it just happened. Until more studies are carried out which show actual consequences of these changes in brain regions we don’t really know what this means for cannabis users.

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9 Comments
  1. Poix Poi says

    LoL, Only a sample size of 40, with little control over possible confounding factors. It is a preliminary investigation at best. I would be very interested in the results of a more large scale controlled study.

    1. Exactly, that’s a sample size of 40 in total, so 20 per group. As you said, its more of a preliminary investigation or observation rather than a full blown study with big implications.

  2. Arnau says

    Great article Ciaran and interesting topic 😉 Could be also good to do these kind of studies in a more “adolescent” population and to try to correlate the changes with behavioral alterations. Thanks for the article!

    1. Yea definitely Arnau, I think there needs to be a behavioural correlate for this to have any real impact. Also, for the Adolescents, it might be hard to get ethical approval to study the effects of an illegal drug in children (under 18). But again, this could be interesting as this is the time when a lot of people begin ‘experimenting’ with drugs!

  3. Laurie says

    Ciaran, just to say people involved in a clinical trial even a small one are supposed to sign a consent for their protection (Ethic) but also, in the interest of the research, to prevent any lie from them. Anyway, you usually can minimize this bias by some calculation.

    1. You’re right Laurie, people do sign consent forms and promise not to lie about things that need to be controlled for like alcohol and cigarette consumption (in the case of this paper), but you can never be 100% sure. People dont want to tell you that they are alcoholics because there is a stigma attached.
      That’s good to know that bias like this can be corrected for with some calculations.

  4. Smigolas says

    Hi Ciaran, great article again!I particularly liked the input from Irish cannabinoid expert, Dr. Eric Downer, very insightful.

    1. Thanks a mil Smigolas! Glad to hear you enjoyed it 🙂

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