DOES CANNABIS FRY YOUR BRAIN?

Some people believe that the use of cannabis should be avoided because it will “fry your brain,” but what does the term “fry” really mean? Our best interpretation of this term and phrase is that it implies that the use of cannabis, either short-term or long-term, will have detrimental effects on the brain and how it functions. While this phrase is quite common and can be used as a scare tactic to dissuade people from using cannabis it does raise the question - is there any scientific merit to it?

Short and Long-Term Effects

Research has observed that the acute use of cannabis does indeed reduce performance on tasks involving memory, cognitive control, and learning (Volkow et al., 2016). However, the deficits observed following a single, acute use of cannabis appear to be temporary, with the effects wearing off after cannabis intoxication subsides (Volkow et al., 2016).

While the cognitive deficits observed with acute use appear to only be temporary, of greater public health concern are the effects of frequent, prolonged cannabis use. While the observed effects are minor, it has been shown that chronic cannabis users have impaired function in a wide variety of cognitive tasks compared to non-users (Grant et al., 2003, Scott et al., 2018). It is important to note that the effects of cannabis on cognition appear to depend on the dosage and timing of cannabis use. In addition, it is challenging to account for other factors (such as the use of other drugs and alcohol) that may at least partially account for cognitive differences between cannabis users and non-users. Finally, these effects are dependent on the individual and can vary from person to person.

Cannabis Use in Adolescents

The largest impacts on cognition and brain development are observed in frequent cannabis users and in individuals who started using as adolescents. When combining results across all studies, there are minimal decreases in IQ (~2 IQ points) among those who have tried or used cannabis; however, these decreases are larger and more significant among adolescents who frequently used cannabis or met cannabis dependence criteria (Power et al., 2021).  But why is this?

Our body naturally produces compounds known as endocannabinoids that interact with a variety of receptors spread throughout the body that make up what is known as the endocannabinoid system. The endocannabinoid system is heavily localized in the brain, and adolescents (people aged 10 through 19) may be at particular risk for cognitive impairment, due to the prominent role that the endocannabinoid system has in neural development and brain maturation (Lubman et al., 2015).

Are the Effects Permanent?

Many studies on adult cannabis users indicate that memory and learning impairments are not permanent and dissipate after a period of time once cannabis use has ended (Scott et al., 2018). One such study looked at brain volume reductions in chronic cannabis users and found that participants who use products containing CBD or completely abstain from cannabis use for a few months have similar brain volumes when compared to non-users (Yücel et al., 2016). Other work found that performance on cognitive tasks returns to the same level as non-users after abstaining from cannabis. There is some discrepancy in how long this abstinent period should be to observe these effects, but estimates range from 3 to 25 days (Scott et al., 2018; Schreiner and Dunn, 2012).

Unfortunately, there is still little known about the reversibility of these effects when cannabis use starts during adolescence. A study from 2010 observed that adolescents who had abstained from cannabis use for at least 5-weeks still had cognitive impairments on a memory task compared to non-users (Jager et al., 2010). This suggests that the cognitive impairments associated with adolescent cannabis use are either not reversible or take longer to remediate compared to adults (Hurd et al., 2019). More research is still needed to fully explain these effects.

Conclusions

While it might be a bit of a stretch to say that using cannabis will “fry your brain,” research does show that both the acute and prolonged use of cannabis may have detrimental effects on the brain and how it functions. Luckily, in adult cannabis users these effects appear to be minor and typically reverse with the cessation of cannabis use; however, this may not be the case in individuals who start using in adolescence. Because of these observations, it is not recommended for individuals under the age of 21 to consume cannabis products.

Contributing Authors: Aaron Fontenot, Austin Drake, Ashley Master, Josh Elmore, & Jonathan Lisano

Check out the studies below for more information:

Arseneault, L., Cannon, M., Poulton, R., Murray, R., Caspi, A., & Moffitt, T. E. (2002). Cannabis use in adolescence and risk for adult psychosis: Longitudinal Prospective Study. BMJ, 325(1), 1212–1213. https://doi.org/10.1136/bmj.325.7374.1212

Camchong, J., Lim, K. O., & Kumra, S. (2017). Adverse Effects of Cannabis on Adolescent Brain Development: A Longitudinal Study. Cerebral cortex (New York, N.Y. : 1991), 27(3), 1922–1930. https://doi.org/10.1093/cercor/bhw015

Grant, I., Gonzalez, R., Carey, C. L., Natarajan, L., & Wolfson, T. (2003). Non-acute (residual) neurocognitive effects of cannabis use: a meta-analytic study. Journal of the International Neuropsychological Society : JINS, 9(5), 679–689. https://doi.org/10.1017/S1355617703950016

Hurd, Y. L., Manzoni, O. J., Pletnikov, M. V., Lee, F. S., Bhattacharyya, S., & Melis, M. (2019). Cannabis and the Developing Brain: Insights into Its Long-Lasting Effects. The Journal of neuroscience : the official journal of the Society for Neuroscience, 39(42), 8250–8258. https://doi.org/10.1523/JNEUROSCI.1165-19.2019

Jager, G., Block, R. I., Luijten, M., & Ramsey, N. F. (2010). Cannabis use and memory brain function in adolescent boys: a cross-sectional multicenter functional magnetic resonance imaging study. Journal of the American Academy of Child and Adolescent Psychiatry, 49(6), 561–572.e5723. https://doi.org/10.1016/j.jaac.2010.02.001

Lubman, D. I., Cheetham, A., & Yücel, M. (2015). Cannabis and adolescent brain development. Pharmacology & therapeutics, 148, 1–16. https://doi.org/10.1016/j.pharmthera.2014.11.009

Power E, Sabherwal S, Healy C, O’Neill A, Cotter D, Cannon M. (2021). Intelligence quotient decline following frequent or dependent cannabis use in youth: a systematic review and meta-analysis of longitudinal studies. Psychological medicine, 51(2), 194-200. https://doi:10.1017/S0033291720005036

Schreiner, A. M., & Dunn, M. E. (2012). Residual effects of cannabis use on neurocognitive performance after prolonged abstinence: a meta-analysis. Experimental and clinical psychopharmacology, 20(5), 420–429. https://doi.org/10.1037/a0029117

Scott, J. C., Slomiak, S. T., Jones, J. D., Rosen, A., Moore, T. M., & Gur, R. C. (2018). Association of Cannabis With Cognitive Functioning in Adolescents and Young Adults: A Systematic Review and Meta-analysis. JAMA psychiatry, 75(6), 585–595. https://doi.org/10.1001/jamapsychiatry.2018.0335

Volkow, N. D., Swanson, J. M., Evins, A. E., DeLisi, L. E., Meier, M. H., Gonzalez, R., Bloomfield, M. A., Curran, H. V., & Baler, R. (2016). Effects of Cannabis Use on Human Behavior, Including Cognition, Motivation, and Psychosis: A Review. JAMA psychiatry, 73(3), 292–297. https://doi.org/10.1001/jamapsychiatry.2015.3278

Yücel, M., Lorenzetti, V., Suo, C., Zalesky, A., Fornito, A., Takagi, M. J., Lubman, D. I., & Solowij, N. (2016). Hippocampal harms, protection and recovery following regular cannabis use. Translational psychiatry, 6(1), e710. https://doi.org/10.1038/tp.2015.201