Youth Cannabis Use: Not so harmless, by Dr Adnan Levent

Youth Cannabis Use: Not so harmless, by Dr Adnan Levent


Cannabis (marijuana) is the most commonly used addictive substance after alcohol and tobacco, in particular among youths. Many countries have already decriminalized its medical and recreational use in recent years. I’ve lost count of the number of times I’ve heard statements like “If it’s legal, it is okay to use” and “If it’s medicine, it must be safe” from both adults and youths. While cannabis may help several health conditions, such as pain and sleep management when used in small doses under a doctor’s control, it can cause lasting harm when abused. This blog aims to raise awareness about cannabis, its use and impact on mental well-being and cognitive functions.  

What is the prevalence of cannabis use? 

As you might be already aware, there is a sharp increase in recreational cannabis use globally in current years. It has been estimated that approximately 200 million people used cannabis worldwide in 2019, representing 4 % of the global population. Compared to the past decade, there is an 18% increase in the number of cannabis users (United Nations Office on Drugs and Crime, 2020). Cannabis use seems to be more spread among youths. In a study from 2020, 44% of university students reported having used cannabis in the previous year, up significantly from 38% in 2015 (Johnston et al., 2022) 

What are the factors that motivate cannabis use in youths? 

There are a number of factors that motivate cannabis use in youths (Benschop et al., 2015): 

  • Euphoria (“it makes me feel happy”) 
  • Enhancement (“it is exciting”) 
  • Social (“it helps me enjoy social events”) 
  • Routine (“I use it because I’m bored”) 
  • Expansion (“it helps me get new viewpoints of things”) 
  • Conformity (“so that I won’t feel excluded”)  

The popularity of cannabis use among younger people may be also associated with a low perception of risk. According to the World Drug Report 2021, the percentage of young people who perceive cannabis as harmful has dropped by 40 per cent, even though cannabis products have almost quadrupled in strength over the period 1995–2019. 

How does the legalisation of cannabis influence its use among youths? 

Cannabis legalisation is unquestionably one of the most controversial topics in our current time. It is anticipated that the prevalence of cannabis use will go up following the recent legalisation of recreational use in many countries and the introduction of a legal cannabis sector. A report in the US from 2014 showed that in states that have legalised cannabis, 40 per cent of secondary school seniors had consumed cannabis, compared with 26 per cent in states where cannabis use is not legal (Johnston et al., 2015).  

How does cannabis work and what are its effects on the body and the brain? 

Despite the widespread of its use, unfortunately, the effects of cannabis use on the body and the brain are often under-recognised. When cannabis is smoked, hundreds of compounds are released in the bloodstream. However, the delta-9-tetrahydrocannabinol (THC) is the main psychoactive ingredient of cannabis. This activates the Endocannabinoid system which is involved in many critical processes such as mood, sleep, appetite, pain-sensation, attention, learning and memory (Kalant, 2014). This means that cannabis use can negatively affect any of these areas.  

Indeed, there is a well-established association between cannabis use and psychiatric disorders, such as anxiety (Mustonen et al., 2021), and depression (Gobbi et al., 2019), specifically among regular and heavy users. Furthermore, extensive studies have revealed that cannabis use impairs:  

  • Attention (Kroon et al., 2021)  
  • Executive functions (Cohen & Weinstein, 2018) 
  • Retrospective memory (La Spada et al., 2019) 
  • Prospective memory (Levent & Davelaar, 2019) 

Those cognitive functions play important role in daily activities such as learning and driving. It is not surprising that cannabis is the drug most often associated with car accidents after alcohol (Legrand et al., 2013). Moreover, cannabis-induced cognitive impairments have been linked to poor academic performance. For instance, students who frequently used cannabis during the first year of university tended to skip more of their classes, earn lower grades and delay graduation (Arria et al., 2015) 

Together, while many people believe cannabis is harmless, the content above highlights its detrimental consequences on both mental health and cognitive abilities, suggesting that there is a disconnect between public perception and real risks associated with cannabis use. 

Are youths more vulnerable to the harmful effects of cannabis use?  

Previous research has established that young people are more vulnerable to the harmful effects of cannabis. For example, a study revealed that despite fairly brief cannabis usage (an average of 2.4 years), young users exhibited similar cognitive impairments relative to adult users with 24 years of use, suggesting that cannabis use is more harmful when it is initiated in early age. A possible explanation is that a teen’s brain is undergoing significant development until approximately 25 years of age (Schneider, 2008), thus the use of cannabis interrupts such developments, causing abnormalities in the brain and behaviours. Compared to later-onset users, early 24-onset cannabis users tended to have smaller whole brain volumes, lower grey matter and higher white matter (Wilson et al., 2000) 

Does cannabis use lead to the use of other drugs? 

According to several studies, young cannabis users are more likely to use more harmful drugs (e.g., cocaine) and develop addiction later in life (Secades-Villa et al., 2015). For instance, a study investigated the impact of cannabis use patterns on the probability of initiation with other illegal drugs in 29,393 teenagers and found that compared to non-users, the risk for other drug use was 21 times higher among cannabis experimenters and 124 times higher among daily cannabis users (Mayet et al., 2012) 

What is the take-home message?  

Cannabis use, especially between the ages of 15 and 24, can lead to various psychiatric disorders and cognitive impairments, possibly due to functional and structural changes in the brain which may affect the quality of life in a general manner as well as the academic and work achievement. It may also increase the risk of using other illegal drugs and developing drug addiction later in life.  

Therefore, any of you who is considering using cannabis for pleasure without medical justification should think about how it might affect your mental health and cognition. You are advised to avoid using cannabis or at least delay the age of first use to protect your brain.  




Arria, A. M., Caldeira, K. M., Bugbee, B. A., Vincent, K. B., & O’Grady, K. E. (2015). The Academic Consequences of Marijuana Use during College. Psychology of Addictive Behaviors : Journal of the Society of Psychologists in Addictive Behaviors, 29(3), 564–575. 

Benschop, A., Liebregts, N., van der Pol, P., Schaap, R., Buisman, R., van Laar, M., van den Brink, W., de Graaf, R., & Korf, D. J. (2015). Reliability and validity of the Marijuana Motives Measure among young adult frequent cannabis users and associations with cannabis dependence. Addictive Behaviors, 40, 91–95. 

Cohen, K., & Weinstein, A. (2018). The Effects of Cannabinoids on Executive Functions: Evidence from Cannabis and Synthetic Cannabinoids-A Systematic Review. Brain Sciences, 8(3), E40. 

Gobbi, G., Atkin, T., Zytynski, T., Wang, S., Askari, S., Boruff, J., Ware, M., Marmorstein, N., Cipriani, A., Dendukuri, N., & Mayo, N. (2019). Association of Cannabis Use in Adolescence and Risk of Depression, Anxiety, and Suicidality in Young Adulthood: A Systematic Review and Meta-analysis. JAMA Psychiatry, 76(4), 426–434. 

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Kalant, H. (2014). Chapter Thirteen—Effects of Cannabis and Cannabinoids in the Human Nervous System. In B. Madras & M. Kuhar (Eds.), The Effects of Drug Abuse on the Human Nervous System (pp. 387–422). Academic Press. 

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La Spada, N., Delker, E., Blanco, E., Encina, P., Caballero, G., Delva, J., Burrows, R., Lozoff, B., & Gahagan, S. (2019). Marijuana Use Associated With Worse Verbal Learning and Delayed Recall in a Sample of Young Adults. Revista Medica de Chile, 147(2), 206–211. 

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Mustonen, A., Hielscher, E., Miettunen, J., Denissoff, A., Alakokkare, A.-E., Scott, J. G., & Niemelä, S. (2021). Adolescent cannabis use, depression and anxiety disorders in the Northern Finland Birth Cohort 1986. BJPsych Open, 7(4). 

Schneider, M. (2008). Puberty as a highly vulnerable developmental period for the consequences of cannabis exposure. Addiction Biology, 13(2), 253–263. 

Secades-Villa, R., Garcia-Rodríguez, O., Jin, C. J., Wang, S., & Blanco, C. (2015). Probability and predictors of the cannabis gateway effect: A national study. The International Journal on Drug Policy, 26(2), 135–142. 

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