Will Weed Make Your Brain Older?

Can recreational drugs be used safely? Do these drugs have long term effects on us? Are all drugs essentially the same? The answer to these tantalizing mysteries lies in the research literature surrounding drugs, which is always expanding. As we learn more about these drugs, we can answer more questions and make more connections that we previously had never thought might have been present. Since recreational drugs, from alcohol to marijuana to heroin, are actively being used by a large group of people, it is important that we have a holistic understanding of the effects that these drugs have on our bodies, both in the short term and throughout a longer span of time spent using them. I would like to focus this blog on just one drug and just one effect that may be associated with: marijuana and its possible connection to cognitive aging.

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As a recreational drug, marijuana has been highly stigmatized in the past, which is something that has been changing more in recent years. Rhetoric about marijuana being a gateway to other more dangerous drugs was prevalent decades ago, but these days it’s more often seen as a harmless pastime. The current rhetoric around it often portrays it as a safe drug that just about everyone does. I would, however, argue that this position is too extreme. Research into the effects of marijuana has been showing that it is associated with some significant negative outcomes which, although they do not directly cause death, are something that people should be aware of.

One side effect that has been associated with long term use of marijuana is a decline in IQ, specifically associated with use throughout adolescence (Fried et al., 2002). There is some dispute as to how much marijuana affects intelligence in general compared to specific domains like vocabulary, the permanence of these effects, and whether or not it is linked directly to marijuana use or other confounding factors (Jackson et al., 2016). Nonetheless, this finding may be confusing to some individuals, since some research has also shown that marijuana use in frequent users does not affect cognitive functioning and some has even found that marijuana use improved performance in certain tasks (Hart et al., 2001; Gruber et al., 2018).

The seemingly contradictory findings relating to marijuana use and certain markers of brain health and cognitive function seem to be related to two factors: age and dosage. In adults, marijuana usage in low doses can improve certain markers of cognitive performance and has even been shown to improve hippocampal neurogenesis. In high doses, however, it has been shown to have the opposite function: being associated with declines in memory, cognition, and neurogenesis. And for younger users, both large and small doses have negative effects on these domains (Calabrese & Rubio-Casillas, 2018). 

Some brain imaging studies have found that marijuana use is associated with the recruitment of more or different brain regions, as compared to non-users, to perform certain tasks (Eldreth et al., 2004). This means that although marijuana users may show comparable or better performance on certain tasks, this performance can be attributed to compensation, signaling that there is a generally worse efficiency in brain function.

It is this point that I would like to connect to the process of cognitive aging, which some models explain through the compensatory mechanisms. In a general sense, these models explain that cognitive tasks become more difficult with age, so more brain regions are recruited in order to maintain sufficient cognitive performance (Dennis et al., 2020). This compensation is a sign of declining brain health over time.

With this considered, it definitely does seem to be possible that marijuana use compels the brain to incorporate more regions in performing a task and that this shouldn’t be taken as a sign of better performance, but rather an indicator that it potentially could be decreasing the efficiency of brain functioning. This is especially alarming, since marijuana is shown to have more consistently negative consequences for younger adults and adolescents. 

One can only speculate a link between this mechanism and potentially negative ramifications for the process of cognitive aging, so I would just end by saying that there needs to be long term research looking into the effects of marijuana use on compensation over the aging process.


Calabrese, E. J., & Rubio‐Casillas, A. (2018). Biphasic effects of THC in memory and cognition. European Journal of Clinical Investigation, 48(5). https://doi.org/10.1111/eci.12920

Dennis, N., Gutchess, A., & Thomas, A. (2020). Overview of Models of Cognitive Aging. In A. Thomas & A. Gutchess (Eds.), The Cambridge Handbook of Cognitive Aging: A Life Course Perspective (Cambridge Handbooks in Psychology, pp. 5-31). Cambridge: Cambridge University Press. doi:10.1017/9781108552684.002

Eldreth, D. A., Matochik, J. A., Cadet, J. L., & Bolla, K. I. (2004). Abnormal brain activity in prefrontal brain regions in abstinent marijuana users. NeuroImage, 23(3), 914–920. https://doi.org/10.1016/j.neuroimage.2004.07.032

Fried, P., Watkinson, B., James, D., & Gray, R. (2002). Current and former marijuana use: preliminary findings of a longitudinal study of effects on IQ in young adults. Canadian Medical Association Journal, 166(7), 887–891.

Gruber, S. A., Sagar, K. A., Dahlgren, M. K., Gonenc, A., Smith, R. T., Lambros, A. M., Cabrera, K. B., & Lukas, S. E. (2018). The grass might be greener: Medical marijuana patients exhibit altered brain activity and improved executive function after 3 months of treatment. Frontiers in Pharmacology, 8. https://doi.org/10.3389/fphar.2017.00983

Hart, C. L., van Gorp, W., Hany, M., Foltin, R. W., & Fischman, M. W. (2001). Effects of acute smoked marijuana on complex cognitive performance. Neuropsychopharmacology, 25(5), 757–765. https://doi.org/10.1016/s0893-133x(01)00273-1

Jackson, N. J., Isen, J. D., Khoddam, R., Irons, D., Tuvblad, C., Iacono, W. G., McGue, M., Raine, A., & Baker, L. A. (2016). Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies. Proceedings of the National Academy of Sciences, 113(5). https://doi.org/10.1073/pnas.1516648113

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