Cannabis & Young Brains

Cannabis is not the only substance that has the potential to impact brain development

By the time you read this, consuming cannabis (marijuana) will be legal for adults in Canada. While the specific regulations need to be clarified and expanded, we know that it will not be available to children. For adults it is generally agreed that occasional limited use will be relatively harmless (leaving aside the short-term impairment that can happen if too much is consumed). For children and adolescents, the concern is that the use of cannabis may negatively impact the brain’s development. Thus, the government has prevented its use by minors.

My knowledge of the brain indicates that the government’s control of cannabis is well grounded. The brain is a complex organ with ~100 billion neurons at birth. Fifty years ago we held a relatively static notion of the brain; it was believed that after puberty the only changes in the brain were a slow decline in the number of neurons till death. We now know that in addition to the major changes in childhood and a slow decline in later life, the brain is developing throughout the teenage years and into at least the early twenties.  

In the first few years of life, there is a large amount of pruning: connections between neurons are maintained only if they are active connections (if synapses are active). A second round of pruning occurs in adolescence. Over a period that extends into early adulthood, a process of myelination occurs: neural connects are covered with a myelin insulation that speeds up signals across neurons a hundred-fold. This process starts in the sensory areas of the brain, then continues in the language areas at around five years old, and lastly extends in the 20s to the front of the brain where “executive functions” occur. This late development of the frontal areas may underlie the impulsive, dangerous behaviours often seen in teenagers – their higher brain functions are not yet fully mature. Additionally, we now know that in several brain areas new neurons are added to the brain and become functional throughout life. 

Cannabis is not the only substance that has the potential to impact brain development, often in a negative manner. It has been well documented that alcohol consumption by pregnant mothers can result in lifelong changes in their children, often related to difficulty with impulse control and emotional problems (Fetal Alcohol Spectrum Disorders). What is relatively harmless in a 30 year old may result in profound disruptions in the normal brain maturation in a child or adolescent.

Access to minors
There is similar concern arising around a new generation of e-cigarettes called “pod mods,” with the most popular brand being the “Juul.” These are smaller rechargeable devices that aerosolize liquids containing nicotine and flavours. The dose of nicotine delivered can be relatively high, and with flavouring it does not have the negative taste effects that many of us experienced with a first cigarette. These pod mods are becoming popular among teenagers, leading to concerns about nicotine’s addicting properties becoming a lifelong temptation. Nicotine administered to rats at puberty can have detrimental cognitive effect in adulthood, and we suspect the same thing may be true in human teenagers. 

Thus, with the changing legal landscape around e-cigarettes and cannabis, the need to restrict access to minors becomes more important. One of the arguments for legalizing cannabis is that it reduces the underground market and makes controlled access easier, with the potential to better restrict sales to adolescents. How well this occurs is a function of government regulation and societal willingness to actively enforce the rules around access. 

I think these legal changes are generally positive, but we must pray for our leaders that they will wisely assume the responsibilities they have been given and regulate psychoactive substances like cannabis and nicotine in a manner that protects our vulnerable children. 


  • Rudy Eikelboom is a Professor of Psychology, at Wilfrid Laurier University, who has emerged from the dark side of the University after being department chair for 9 years and now teaches behavioural statistics to graduate and undergraduate psychology students. His retirement looms and he is looking forward to doing more writing on the implications of modern science for our Christian faith. Currently, he serves as a pastoral elder at the Waterloo Christian Reformed Church.

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