(Information provided by the University of Washington Alcohol & Drug Abuse Institute). www.learnaboutmarijuana.org

Studies have shown that if an adolescent uses marijuana early in life (before the age of 16 years) and for a prolonged period of time, it can lead to a number of significant problems. While prevalence rates have markedly declined over the past decade, marijuana is still widely used by adolescents, and the possible impacts on adolescent development remains an important issue.

How Many Adolescents Use Marijuana?

Marijuana is the illicit drug most likely to be used by teens in the U.S. According to the 2012 Monitoring the Future (MTF) Study, 45.3% of U.S. 12th graders reported having used marijuana once or more in their lifetime, with 22.9% reporting use in the previous 30 days.

In our state, the 2012 Washington State Healthy Youth Survey reported that approximately 19% of students in the 10th grade and 27% of students in the 12th reported current marijuana use, almost double the percentage who smoke cigarettes. Fewer students in grades 8, 10, and 12 perceive a great risk of harm in using marijuana regularly, and among 10th graders, that percentage dropped from 65% in 2000 to 46% in 2012. More than half of Washington’s 10th graders report it is easy for them to get marijuana.

Nationally, while the proportion of students using marijuana decreased from 2011-2012, use was still relatively widespread among secondary school students, particularly older males, and more students are using marijuana daily than they were five years ago (daily use among 12th graders increased from 5.1% to 6.5%). (MTF)

What are the Concerns About Adolescents Using Marijuana?

Adolescence is a period when many developmental changes are occurring. It is a time when a young person’s intellectual capacities expand and their friends and peers become increasingly influential.

Adolescent use of marijuana has been linked to a range of developmental and social problems. A 2012 study of over 1,000 individuals followed from birth through midlife found that persistent cannabis use was associated with neuropsychological decline across numerous domains, including cognitive and memory problems and declining IQ. Further, cessation of marijuana use did NOT fully restore neuropsychological functioning among adolescent-onset cannabis users (Meier et al, 2012).

Early initiation of marijuana use can have an impact on the following:

  • Memory, Attention and Learning
    • Affect memory, attention and ability to think clearly, making it difficult to concentrate, learn new things, and make sound decisions (Dougherty et al, 2013)
  • Affect movement and balance while intoxicated
  • Be associated with a moderate decrease in IQ in heavy current marijuana users (Meier et al, 2012).
  • School Performance
    • While it is difficult to distinguish whether this is due to learning difficulties, lack of motivation, or because marijuana users mix with peers who may be involved in a range of risk taking behaviors (McCaffrey DF et al, 2010),
    • Poorer school performance
    • Increased absences from school
    • Increasing the risk of dropping out without graduating.
    • In Washington State, the Healthy Youth Survey results for 2012 found that, statewide, high school students who used marijuana were more likely to get lower grades in school (Cs, Ds, or Fs) compared to those that don’t use.
  • Problematic Behaviors
    • Studies have shown that those who use marijuana from an early age are at risk of later developing problems, characterized by social disadvantage, behavioral difficulties, and problematic peer affiliations.

A 2008 longitudinal study of heavy cannabis users from ages 14 to 25 in a New Zealand birth cohort found that increasing cannabis use in late adolescence and early adulthood is associated with a range of adverse outcomes in lager life. High levels of cannabis use are related to poorer educational outcomes, lower income, greater welfare dependence and unemployment, and lower relationship and life satisfaction. These findings add to a growing body of knowledge regarding the adverse consequences of heavy cannabis use. However, this study primarily established correlation rather than causality (Ferguson & Boden, 2008).

Using marijuana at an early age is also linked to higher risk taking behavior such as:

  • Higher levels of leaving the family home
  • Immature sexual activity, which can result in unplanned pregnancy (Bryan et al, 2012)
  • Increased risk of driving while under the influence of marijuana; marijuana use more than doubles a driver’s risk of being in an accident (Ashbridge et al, 2012)
  • Higher levels of criminal behavior such as motor vehicle theft and break-and-enter offences to pay for drug use
  • Increased Risk of Mental Health Issues

Marijuana use has been linked to a range of mental health problems such as psychosis, depression or anxiety. A 2002 study in Sweden found that heavy cannabis use at age 18 increased the risk of later schizophrenia sixfold (Arseneault et al, 2002). Since then, numerous additional studies have found a similar correlation between adolescent marijuana use and psychosis or schizophrenia, especially in teens with a family history of the disorder (Copeland et al, 2013).

The potential for depression and anxiety is also increased in adolescent marijuana users. The nature of this relationship is controversial, with some studies not supporting a causal association, but instead linking depression due to marijuana’s contributions to learning difficulties, poorer educational outcomes, and problematic behaviors. However, a 2012 study found that increasing frequency of marijuana use was associated with increasing symptoms of depression, with the association stronger in adolescence and declining into adulthood (Horwood et al, 2012).

Using marijuana from an early age places the person at risk of:

  • Impaired emotional development
  • Increased risk of becoming more dissatisfied with life
  • Increased likelihood to suffer from depression, anxiety, psychosis, or other mental illness