Effets de la consommation de cannabis chez les adolescents

Introduction

Cannabis is a significant political, health and law-enforcement issue. With new evidence, opinions and perspectives being released and discussed every day — covering a broad spectrum of considerations — 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.

In North America, a number of USA States have legalized cannabis use, and the public discourse on cannabis tends to focus on sociopolitical and legal issues: assessing the economic impact of legalization or decriminalization, for instance or considering cannabis use for medical purposes.

In Europe a small number of countries tolerate individual small quantities and the debate is still going on.

What motivates youth to use cannabis

Like adult cannabis users, youth report feelings of increased sociability and euphoria when using cannabis. Yet youth also describe a number of other factors that motivate their cannabis use, which can be divided into five distinct categories: enhancement (“it’s exciting”); social (“it helps me enjoy a party”); coping (“it helps me forget about my problems”); expansion (“it helps me understand things differently”); and conformity (“so I won’t feel left out”). Recently, this list has been extended to include routine (“I use it out of boredom”).

Cannabis use can also be looked at in terms of expectancies, which reflect an individual’s beliefs about the experiences that will result from cannabis use and can be grouped into two domains: negative, and positive expectancies. Adolescents who delay initiating cannabis use tend to have high negative expectancies; those who start using cannabis with greater frequency typically have high positive expectancies.

These expectancy domains include cognitive and behavioral impairment, relaxation and tension reduction, social and sexual facilitation, perceptual and cognitive enhancement, physical effects and cravings, and overall negative effects.

What are the acute effects and risks of cannabis use on youth?

While some people, especially inexperienced users, will experience unpleasant events such as intense anxiety, panic and psychotic symptoms when using cannabis, the risk of overdose is extremely low, even among individuals with the highest levels of use. Acute cannabis intoxication has been linked to deficits in attentional focus, information processing, motor coordination and reaction time.

Perhaps the most significant acute 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.

Actually, dose, potency and cumulative exposure, all contribute to the potential effects of cannabis use in youth. Of these factors, dose has been less studied due to the fact that the amount of active ingredient youth are exposed to during each episode of use, varies according to the overall substance content (i.e., proportions of cannabis and non-cannabis ingredients), the amount of active ingredient (e.g., THC, cannabidiol), the mode of administration (e.g., joints, vaporizers), and individual versus shared use.

Cannabis use can lead to hospitalization: in Canada in 2011, approximately 1,600 hospital stays were recorded as being primarily due to a cannabinoid- related disorder to be compared with nearly 20,000 hospital stays due to alcohol-related disorders during that same time period. Youth between the ages of 15 and 24 are likely to stay in hospital longer than other age groups.

What about the risk of dependence to cannabis use in youth?

The risk of dependence (i.e., lack of control over use of cannabis despite the associated harms) is approximately 9% among individuals with any lifetime cannabis use and approximately 16% among those who initiated cannabis use during adolescence.

When compared to alcohol and tobacco, among adolescents, cannabis use has a higher rate of transition to either other drugs or to substance abuse problems.

What are the long-term effects related to cannabis use by youth?

Numerous studies indicate that cannabis use can result in a number of short- and long-term physical, mental and psychosocial effects and this is a great concern. Specifically, evidence suggests that “regular” or “heavy” cannabis use, which is typically defined as daily or near-daily use beginning in adolescence — is associated with a wide range of poor outcomes that may have dose-response characteristics.

In studies where strong evidence for a connection with daily or near-daily (high-frequency) use, it was observed that:

• Long-term regular use that starts in adolescence has been found to be associated with impairments in attention, memory and verbal learning. There is also evidence that, among long- term daily cannabis users, these deficits coalesce into declines in IQ, although some have challenged this finding. 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.
• Symptoms of tolerance (a lower effect of the same dose) and withdrawal (a negative reaction when intake of the drug is stopped, such as depression, insomnia, anxiety and disturbances in appetite), are reported by some cannabis users, experienced typically in the context of high-frequency, long-term use.
• Regular cannabis use in adolescence is also associated with experiencing psychotic symptoms, especially when there is a family or personal history of psychotic disorders. The risk of reporting psychotic symptoms or being diagnosed with schizophrenia in adulthood is doubled in individuals with regular cannabis use in adolescence.
• While the evidence is not as strong regarding other mental health issues, there are possible links between regular cannabis use in youth and increased risk for depression and suicide.
• 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, especially the ongoing development and maturation of the prefrontal cortex, which is critical to higher-order cognitive processes such as impulse control, working memory, planning, problem solving, and emotional regulation.
• Adolescent brain development is also affected by the endocannabinoid system. Endocannabinoids (cannabinoids naturally occurring in the body) regulate the activity of neurotransmitters like dopamine and serotonin, which in turn affect memory, coordination, appetite, pain, mood, pleasure and motivation. Cannabis use can disrupt the functioning and development of these systems.

In Canada, how are the youth using cannabis and how do they perceive it?

Canadian youth use cannabis more than any other illicit drug and many start using it as early as late elementary school. Daily or near-daily cannabis use by adolescents is associated with increased harm and the rates for this type of heavy cannabis use range from 1% to 6%. The high-frequency use of cannabis reported by some students is problematic. The acute 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.

According to the 2013 Canadian Tobacco, Alcohol and Drugs Survey, about a quarter of youth aged 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, of whom only 8.0% reported past-year cannabis use. According to UNICEF, they are the highest users in the developed world amongst people of their age.

In general, young Canadian people have a wide range of opinions about cannabis, some reflect inaccurate information and others reflect conflicting messages received through the media, peers and adults. For example, some youth have expressed the belief that cannabis can prevent — or even cure — cancer. 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.

In Canada, the youth perceive cannabis use to be widespread, not just among their peers but also among adults as well. It is often described as a substance “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. In the United States, evidence from the Monitoring the Future Study shows among high school seniors over the past 40 years, an inverse association between the perception of the risk associated with cannabis use and past-year use.

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

Many studies of cannabis-related outcomes have lacked methodological rigor and do not provide adequate and reliable evidence regarding the direction of influence. Did the psychosocial or health problem exist before the cannabis use and increase the risk of cannabis use? Did cannabis use lead to the psychosocial or health problem? Or was there a common factor that led to both the psychosocial or health problem and the cannabis use? Moreover, examination of the biological indicators of the actual cannabinoid doses consumed has been lacking, limiting the extent to which conclusions about causality can be drawn.

While progress continues to be made in recognizing and understanding cannabis problems in youth, their causes and mechanisms, their long-term effects, and their prevention and treatment, there are still many questions. Prevention and treatment of cannabis problems in adolescents and young adults are not yet at the level of efficacy that our society would wish.

There is a need for more research and better data in particular on adverse effects to inform policy, practice and programs, on improved pharmacological and psychosocial treatment methods and follow-up studies of their long-term efficacy.

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, and to provide the best possible information to these young people.