The Evidence

Health risks

Cannabis is not a benign substance. Public health experts identify these as the main health risks:

  • Problems with thinking, memory or physical co-ordination
  • Impaired perceptions or hallucinations
  • Fatal and non-fatal injuries, including those from motor-vehicle accidents, due to impairment
  • Mental health problems and cannabis dependence
  • Chronic respiratory or lung problems
  • Reproductive problems

Public health experts recommend reducing risks to your health by taking these steps, including: abstaining from cannabis use, delaying taking up cannabis use, choosing lower-risk cannabis products, limiting and reducing cannabis use, not driving or operating machinery while impaired, and avoiding cannabis use if you are at risk for mental health problems or are pregnant.


Fischer et al (2017). Canada’s Lower-Risk Cannabis Use Guidelines (LRCUG) Retrieved at:

Use of cannabis in the past year:

  • General population, 15 years of age and up: 12 %
  • Past year use males: 15 %
  • Past year use females: 10 %
  • Adults, 25 years of age and up: 10 %
  • Youth, 15 to 24 years of age: 25.5 %
  • Youth, 15 to 19 years of age: 21 %
  • Youth, 20 to 24 years of age: 30 %
  • Median age of initiating cannabis use: 17 years of age


Canadian Tobacco, Alcohol and Drugs Survey (CTADS) (2015 summary). Retrieved at:

Effects of cannabis use on youth

  • Adolescents are particularly at risk for harms since their brains are undergoing development into their early 20s.
  • Cannabis use during adolescence can cause functional and structural changes to the brain leading to damage.
  • The research suggests a strong association between daily cannabis use and depression in adolescents and young adults although no causal relationship has been established.
  • Cannabis use can produce psychosis in adolescents even among those without a prior history in mental illness. Although the absolute risk for producing psychosis is low.


Canadian Centre on Substance Use and Addiction. Marijuana and Youth. Retrieved at:

Canadian Paediatric Society, position statement (2017). Cannabis and Canada’s Children and Youth. Retrieved at:

Drug-impaired driving

  • Cannabis use is associated with an increased risk of a motor vehicle crash especially for fatal collisions.
  • Cannabis is the most commonly found drug among fatally-injured drivers in Canada.
  • Nearly half of cannabis users surveyed who drive in Ontario have reported driving while impaired.
  • In 2012, cannabis collisions in Canada resulted in an estimated 75 fatalities, 4,407 injuries and 7,794 victims of property damage only (PDO) collisions, with an estimated economic and social cost of approximately $1 billion.
  • 16–34 year olds represent only 32% of the Canadian population, but 61% of the cannabis-attributable fatalities.


Ashbridge et al (2012). Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis, British Medical Journal. Retrieved at:

Solomon et al for MADD Canada (2018). Cannabis and other drugs among drivers of highway vehicles dying within 30 days of a crash on a public road: Canada, 2014. Retrieved at: Oct. 4, 2018. Nearly half of Ontario cannabis users polled have driven under the influence: CAA. Retrieved at

Canadian Centre on Substance Use and Addiction. Driving Under the Influence of Cannabis. Retrieved at

Wettlaufer et al (2017). Estimating the harms and costs of cannabis-attributable collisions in the Canadian provinces. Retrieved at:

Share This