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Effects of cannabis use by teens

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Context - Cannabis is one of the most widely used illicit drug. Are teens well informed about the risks associated with it ?

What are those risks ?

This is a faithful summary of the leading report produced in 2015 by Canadian Centre on Substance Abuse (CCSA): " The Effects of Cannabis Use during Adolescence" 

  • Source document:CCSA (2015)
  • Summary & Details: GreenFacts
Latest update: 1 April 2016


Cannabis is a significant political, health and law-enforcement issue. Across North America, the public discourse on cannabis tends to focus on sociopolitical and legal issues. With evidence, opinions and perspectives being released and discussed every day the public has become increasingly confused about cannabis’ status, prevalence and effects. For teenagers, making decisions about cannabis without having a good knowledge of the facts can have profound consequences.

What are the direct safety risks of cannabis use?

Some people, especially inexperienced users, can experience very unpleasant events such as intense anxiety, panic and psychotic symptoms when using cannabis. However the risk of overdose is extremely low, even among individuals with the highest levels of use.

Perhaps the most significant safety concern for youth is driving under the influence of cannabis. In student surveys, approximately 10–20% of student who have a driver’s license, reported driving within one hour of using cannabis, which is nearly identical to the rates reported for driving under the influence of alcohol. Although evidence suggests that it is not quite as dangerous as driving under the influence of alcohol, driving under the influence of cannabis is still associated with a significantly increased risk of collision and injury; that risk increasing further when driving under the influence of both alcohol and cannabis.

Cannabis intoxication has also been linked to deficits in attentional focus, information processing, motor coordination and reaction time.

What are the short- and long-term effects of cannabis use?

Numerous studies indicate that cannabis use can result in a number of short- and long-term physical, mental, and psychosocial effects. In studies where strong evidence for a connection with cannabis use has been found, the following variables were linked to “regular” or “heavy” cannabis use, which is typically defined as daily or near-daily use :

  • When compared to alcohol and tobacco, among adolescents, cannabis users have a higher rate of transition to either other drugs or to substance abuse problems.
  • The risk of dependence is approximately 9% among all people who use cannabis, and approximately 16% among those who started use during adolescence.
  • Symptoms of tolerance and withdrawal, such as depression, insomnia, anxiety and disturbances in appetite, are reported, typically in the context of high-frequency, long-term use.
  • Regular cannabis use in adolescence is associated with experiencing psychotic symptoms, such as schizophrenia, and also with a possible increased risk for depression and suicide. Long-term regular use that starts in adolescence has also been found to be associated with impairments in attention, memory and verbal learning.

What are the possible consequences of cannabis use during adolescence?

Adolescents are more sensitive than adults to the adverse effects of regular heavy use of cannabis, including cognitive impairment, dependence, poor psychosocial development, impaired school and work performance, drug-related psychiatric illness, and generally poorer treatment outcomes.

In some contexts, the long-term cognitive impairments that result from regular cannabis use have been reversed, but this appears less likely for heavy use that begins in adolescence. Youth might be particularly vulnerable to these negative outcomes due to the extensive structural and neurochemical changes that are taking place in the brain during adolescence. In general, the earlier the use of cannabis started, the more risk there is of long term problems.

As the effects of cannabis can impact learning and schoolwork completion, youth who use cannabis regularly are more likely to drop out of high school and, in turn, less likely to pursue post-secondary education. In addition, youth who are already vulnerable to poor educational outcomes due to other factors might be more likely to use cannabis regularly and affiliate with peers who also use cannabis.

What are the actual limits of the available studies on the effects of cannabis use?

Given the high rates of cannabis use by youth during this critical period of their development — as well as the multitude of cannabis-related information being released and discussed every day — it is more important than ever to review what is known, what is not known and what evidence is emerging about the effects of cannabis use during adolescence. Preventive education programs delivered in schools or healthcare facilities are highly variable in content and execution, but the best ones can delay the commencement of use by 20–40% compared to the outcome in groups not attending such programs.

How is cannabis perceived and used by Canadian youth?

In Canada, use of cannabis is more prevalent than the use of any other illicit drug, and many start consuming it as early as late elementary school. About a quarter of youth in age groups 15-19 and 20-24 reported past-year use of cannabis. In total, youth use cannabis at a rate 2.5 times higher than adults aged 25 and older.

While the current levels of past-year cannabis use are concerning, more problematic is the high-frequency use of cannabis reported by some students. Daily or near-daily use by adolescents is associated with increased harm and the rates for this type of heavy cannabis use range from 1% to 6%.

In Canada, the youth has a wide range of opinions about cannabis, some of which are misconceptions, and conflicting messages received through the media, peers and adults. They perceive cannabis use to be widespread: it is something that “everyone” is using “all the time.” They also believe cannabis to be relatively harmless, viewing it as a more “natural” substance that is not really a drug at all. Youth have also expressed mixed beliefs about cannabis’ impact on one’s ability to drive, with some stating that using cannabis improves driving performance and is not as dangerous as drinking and driving. It is therefore of paramount importance to provide the best possible information to these young people.

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