Canadian Centre on Substance Use and Addiction

After alcohol, cannabis is the second most commonly used substance in Canada. There is a lot of information available on the Internet about the health impacts and potential benefits of cannabis use. Some of this information is accurate and some is inaccurate. The research section summarizes the current scientific evidence on the health impacts of cannabis, the potential medical benefits of cannabis and peoples’ perceptions of cannabis.

Health Impacts
of Cannabis

Health Impacts of Cannabis

While the evidence on the medical applications of cannabis is limited, there are risks associated with regular cannabis use. Ongoing research is improving what we know about both risks and benefits.

The Clearing the Smoke on Cannabis series looks at how cannabis use affects mental and physical health, and discusses implications for policy and practice. Prepared and peer-reviewed by expert researchers in the field, this series addresses what we know about the health effects of cannabis use, what we don’t know and what needs further investigation.

Medical use of cannabis and cannabinoids

Promising research indicates that cannabis and cannabinoids are effective in relieving symptoms associated with certain severe and chronic conditions. As of June 2018, over 333,000 Canadians had registered to access cannabis for medical purposes.

  • There is good evidence that cannabis and cannabinoids can be effective for treating nausea, vomiting and pain associated with certain chronic conditions.
  • Research is also being conducted to determine if cannabis and cannabinoids are useful for managing symptoms associated with multiple sclerosis, epilepsy, cancer, obesity and glaucoma, as well as inflammatory diseases, and psychiatric and neurodegenerative disorders.
  • There are risks and harms associated with the medical use of cannabis, including lack of standardized dose information and impacts on cognitive abilities, such as attention and memory.
  • Health practitioners and clients need more evidence, including the results of clinical trials, to support them in making informed decisions. 
  • Individuals should speak to their healthcare provider before making a decision about using cannabis for medical purposes.

Chronic cannabis use and cognitive functioning

Starting to smoke Cannabis earlier in life — before 16 or 17 — is one of the strongest predictors of noticeable cognitive difficulties. However, the impact of regular cannabis use on cognitive functions is generally mild for most people. Many of the measurable effects on these functions disappear after sustained periods of not using cannabis.

  • Regular cannabis use is associated with changes in brain structure and function, including changes to the brain’s natural reward pathways.
  • Individuals who display risky and impulsive decision-making are more likely to develop problematic cannabis use and cannabis use disorder.
  • Establishing a standardized measurement of cannabis use, including frequency of use, dosage and methods of consumption, is required to explore the causal nature of these relationships.

Chronic cannabis use and mental health

People who use cannabis regularly — one or more times per week over a period of months or years — could be at greater risk of developing psychosis or schizophrenia. This finding was determined through a review of the current body of research about the relationship between cannabis and a number of mental health conditions.

Additional findings of the report include:

  • People with mental health conditions are more than twice as likely to use cannabis regularly.
  • Regular cannabis use is generally associated with more harmful rather than beneficial effects among people with mental health conditions.
  • A standardized measurement of cannabis use and larger studies are needed to understand better the relationship between cannabis and mental health.

Respiratory effects of smoking cannabis

Individuals who smoke cannabis on a regular basis commonly report coughing on most days, as well as wheezing, shortness of breath after exercise, chest tightness at night, sounds in their chest, early morning phlegm and bronchitis. Abstinence can reverse some of the negative respiratory symptoms experienced by those who smoke cannabis.

Research on the respiratory effects of smoking cannabis provides the following observations:

  • Cannabis smoke contains many of the same chemicals as tobacco smoke.
  • Evidence about the link between cannabis smoking and lung cancer is mixed.
  • There is currently no causal evidence between cannabis smoking and COPD.
  • At present, it is unclear how vaping and second-hand cannabis smoke affect an individual’s respiratory system.

Cannabis use during pregnancy

An estimated 16.9% of individuals of childbearing age (15–44 years) reported past-year use of cannabis in 2015 and 2% to 5% of pregnant individuals reported using cannabis during pregnancy. There is little evidence to suggest an association between cannabis use during pregnancy and increased risk of premature birth, miscarriage or major physical abnormalities. However, frequent cannabis use during pregnancy is associated with:

  • Low birth weight and is part of a cluster of risk-factors correlated with other adverse birth outcomes;
  • Altered neurodevelopment and cognition, and academic under-achievement; and
  • Behavioural disturbances among children and young adults, including attention deficits, increased hyperactivity and impulsivity, and increased likelihood of delinquency and substance use.

Costs of
Cannabis Use

Costs of Cannabis Use

Cannabis is one of the most commonly used substances in Canada. According to the 2018 National Cannabis Survey, 15.6% of all Canadians reported using cannabis in the past three months. While the non-medical use of cannabis can result in numerous health impacts, it also contributes to the overall cost of substance use. The greatest impact is in the criminal justice sector, and other sectors impacted include healthcare, business and industry, as well as other areas such as research and prevention, damage to property and motor vehicles, and workplace costs not covered in lost productivity.

  • In 2014, cannabis use contributed $2.8 billion dollars (7.3%) to the overall cost of substance use.
  • Between 2007 and 2014, per-person costs increased by 19.1% for cannabis.
  • Between 2007 and 2014, cannabis-related healthcare costs increased by 27.9%.
  • In 2014, cannabis was responsible for the third highest substance use-related crime costs ($1.8 billion or 19.7%), of which 60% of costs were associated with violations of the Controlled Drugs and Substances Act.
  • In 2014, cannabis accounted for 18% of other direct costs.

For more information, see the full report:

Canadian perceptions
and trends

Canadian perceptions and trends

Demographic trends
for cannabis use

Cannabis use in Canada is slowly on the rise: past-year use among the general population (aged 15 years and over) increased from 10.6% in 2012 to 12.3% in 2014. In addition, Canadian youth were more than twice as likely to report past-year cannabis use compared to adults, with the use rates among individuals aged 15–24 years and individuals aged 25 years and older being 25.5% and 9.9% respectively.

For more information see the Cannabis (Drug Summary), the National Cannabis Survey (second quarter 2018) and the Canadian Cannabis Survey (2017).

Canadian perceptions
on cannabis

Since the Cannabis Act was passed in October 2018, Canadians have been voicing their concerns and perspectives about the health and safety impacts of cannabis. In 2018, CCSA commissioned a Nanos poll wherein 1,000 Canadians were asked a series of questions about their thoughts on cannabis use. Some of the results include:

  • Over 80% of Canadians say that schools should play a role in educating youth about cannabis use;
  • Canadians’ top concern about the legalization of cannabis is individuals driving or working while impaired;
  • The majority of Canadians say they are knowledgeable or somewhat knowledgeable about the health effects of cannabis;
  • Close to 90% of of Canadians agree or somewhat agree that they would feel comfortable talking to their doctor about cannabis; and
  • Most Canadians say they are confident or somewhat confident that they know the effects of cannabis on driving.

Perceptions of cannabis by Canadians aged 16 years and older

According to Health Canada’s Canadian Cannabis Survey summary report (2017), Canadians aged 16 years and older held the following opinions about cannabis:

  • Non-medical cannabis use is more socially acceptable than tobacco use.
  • The majority of those who used cannabis in the past year stated that it had no effect on their work, studies, home life, marriage or physical health.
  • About half of those who used cannabis in the past year stated that it positively influenced their mental health, quality of life, friendships and social life.
  • About half of the participants stated that cannabis had a positive effect on a person’s mood, creativity, anxiety and sleep.
  • Most participants concluded that cannabis use had a negative effect on a person’s motivation and ambition, memory, concentration, attention, thinking and decision making.
  • The majority believe that cannabis can be habit-forming.

For more information, see the full report: Canadian cannabis survey 2017 - Summary.

Perceptions of cannabis
by Canadian youth

In addition, a small sample of Canadian youth aged 15–19 held the following opinions about cannabis:

  • Cannabis is a natural plant, not a drug, and therefore is safe.
  • Cannabis can give the user positive effects such as focus, relaxation, ability to sleep and creativity.
  • Cannabis effects depend on the people who use it; the effects have more to do with the person and their attitudes than the drug itself.
  • Cannabis makes people better drivers because it increases their focus.
  • Cannabis is not addictive and stopping use of it does not lead to withdrawal symptoms.
  • Cannabis is not harmful, especially compared to alcohol and psychoactive prescription drugs.

Driving under the
influence of Cannabis

Driving under the influence of Cannabis

Cannabis impairs the cognitive and motor abilities necessary to safely operate a motor vehicle and doubles the risk of crash involvement. Current data supports the following conclusions:

  • Among young drivers in Canada, driving after using cannabis is more prevalent than driving after drinking.
  • Males are three times more likely than females to drive after using cannabis.
  • After alcohol, cannabis is the most commonly detected substance among drivers fatally injured in traffic crashes in Canada.

Youth and Cannabis

Youth and Cannabis

With the legalization of cannabis, youth are seeking credible information from individuals they know and trust on the benefits and harms of cannabis use. They want to know the whole story. Young people are ready to have the conversation, but many who interact with them are not well prepared for it.


To help those looking for practical approaches to talking with youth about cannabis to feel more confident in having these difficult conversations, CCSA developed a communication guide to help educate youth allies on how to have safe, unbiased and non-judgmental conversations with young people about cannabis. By taking a harm reduction approach and providing a basis for communicating accurate information about cannabis, youth allies will be able to better support young people in making informed decisions about their cannabis use.

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