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.

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).  A contradctory (and surpising) finding was reported in a recent longitudinal study that followed males from adolescence into their mid-thirties, which found no differences in any of the mental or physical health outcomes measured regardless of the amount or frequency of marijuana used during adolescence. (Bechtold, 2015)

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

Memory, attention, and learning

Early and continued use of marijuana can:

  • 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), though this study has been challeged for its methodology.

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), using marijuana at an early age is independently associated with:

  • 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 later 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.

Other concerns about use of marijuana by adolescents

  • Use of marijuana by adolescents is illegal in Washington State and all other states in the U.S. It is an offence to cultivate, possess, use, sell or supply marijuana. Doing so could result in criminal prosecution or even incarceration, depending on the type of offence and which state it was committed in.
  • Marijuana can have short- and long-term consequences on health. See Health Effects topic page.
  • Marijuana use can increase the risk of psychotic episodes or trigger a mental illness. See Marijuana and mental health.
  • Marijuana use can lead to dependence in young people who use it regularly over a period of time.
  • Relationships with family and other friends who don’t use marijuana may become problematic.
  • Using marijuana has been associated with a decrease in motivation, which can impact school, work, family, friends and life in general.
  • The cost of using marijuana can result in financial difficulties.

Related resources

References

  • Arseneault L, Cannon M, Poulton R, et al. Cannabis use in adolescence and risk for adult psychosis: Longitudinal prospective study.  BMJ 2002;324:1212. View abstract
  • Ashbridge M, Hayden JA, Cartwright JL.  Acute cannabis consumption and motor vehicle risk: Systematic review of observational studies and meta-analysis.  BMJ 2012;344:e536. View abstract
  • Bechtold J, Simpson T, White HR, et al. Chronic adolescent marijuana use as a risk factor for physical and mental health problems in young adult men. Psychol Addict Behav 2015;29(3):552-563. View abstract
  • Bryan AD, Schmiege SJ, Magnan RE.  Marijuana use and risky sexual behavior among high-risk adolescents: Trajectories, risk factors, and event-level relationships.  Dev Psychol 2012;48(5):1429-42. View abstract
  • Copeland J, Rooke S, Swift W. Changes in cannabis use among young people: impact on mental health. Curr Opin Psychiatry 2013:26:325-329. View abstract
  • Dougherty DM, Mathias CW, Dawes MA, et al. Impulsivity, attention, memory, and decision-making among adolescent marijuana users.  Psychopharmacology 2013;226(2):307-319. View abstract
  • Fergusson DM, Boden JM. Cannabis use and later life outcomes. Addiction 2008;103 (6): 969–976; discussion 976–8. View abstract.
  • Horwood LJ, Fergusson DM, Coffey C, et al. Cannabis and depression: an integrative data analysis of four Australasian cohorts. Drug Alcohol Depend 2012;126:369-378. View abstract
  • McCaffrey DF, Pacula RL, et al. Marijuana use and high school dropout: The influence of observables. Health Econ 2010;19(11): 1281-1299. Free online.
  • Meier MH, Caspi A, Ambler A, et al.  Persistent cannabis users show neuropsychological decline from childhood to midlife.  Proc Natl Acad Sci USA 2012;109:E2657-64. View abstract

Updated 2015. This information adapted with permission from the National Cannabis Prevention and Information Centre in Australia.