Skip to main content


Cannabis (marijuana)

What is cannabis?

Cannabis is a plant from which marijuana and other mind-altering (psychoactive) products are made. Marijuana is produced from the dried leaves and flowers of the cannabis plant. (The words “cannabis” and “marijuana” are often used interchangeably). Other terms for marijuana include weed, pot, grass, reefer and many more. Hashish (hash) and hash oil are made from the resin of the cannabis plant.

Why do people use cannabis?

Cannabis is used almost exclusively for recreational and medical purposes.

Recreationally, people use it for its mind-altering effect, which is usually described as a “high” (see “What are the effects” below).

Those who use cannabis medically seek to relieve symptoms of health problems. Cannabis is not an approved therapeutic product in Canada; however, “The courts in Canada have ruled that the federal government must provide reasonable access to a legal source of marijuana for medical purposes.”  Symptoms that cannabis has been used to manage include chronic nerve pain, severe nausea or vomiting in cancer chemotherapy, loss of appetite or weight in people with HIV/AIDS, and pain and muscle spasms in multiple sclerosis.

How is cannabis used?

Cannabis is consumed in a variety of ways, the most common of which is through inhalation. Cannabis is often rolled into a “joint” that resembles a cigarette and smoked. The flowers of the plant can be burned in devices such as a pipe, a bong or a hookah, which creates smoke that is inhaled. It can also be heated in a device called a vaporizer that doesn’t burn the plant; rather it heats it to a temperature that releases a gas that is inhaled (vaped).

Other ways to consume cannabis include eating it (e.g. hash brownie) and drinking it in the form of a tea. Edibles have a delayed onset and the effects last longer.

Medicinal preparations derived from the cannabis plant include patches, lotions/topical creams, drops or sprays. Learn more.

What are the effects of cannabis?[1]

The cannabis plant contains hundreds of compounds that have numerous and varied effects on the body and mind.  Many of these compounds are classified as cannabinoids. Tetrahydrocannabinol (THC) is the main cannabinoid that is responsible for cannabis’ psychoactive effects (i.e. the “high”). Cannabidiol (CBD) is a non-psychoactive cannabinoid that modifies some of the effects of THC.

The effects of cannabis on a user depend on a variety of factors and are different from one person to another. They depend on the combination of substance, user and context:


  • How much is used
  • How often it is used
  • How long the user has been consuming
  • The method of consumption (e.g. smoked, vaped or eaten)
  • The concentration of THC & CBD
  • The consumption of other substances including alcohol, illegal drugs, and prescription medications


  • The user’s mood and expectations
  • The user’s age
  • The user’s health, which includes medical and psychiatric conditions
  • How long the user has been consuming


  • The environment in which it is used
  • The moment of the day
  • With whom it is used
  • Presence of conflicts


The effects of cannabis use can be placed into two categories: Short-term & Long-term effects:

Short-term effects

For a majority of users, these occur shortly after cannabis is consumed into the body and last for a few hours.

Psychological effects (i.e. the “high”) include:

  • Euphoria
  • Decreased inhibition
  • Relaxation
  • Changes in consciousness (e.g. heightened appreciation of art, music and humour)
  • Distortions in sensory experiences (e.g. time passes more slowly, distances become distorted, taste is heightened)
  • Increased sensuality and libido

Physiological effects include:

  • Red eyes
  • Dry mouth
  • Increased appetite
  • Increased heart rate

Behavioural effects include:

  • Laughter
  • Talkativeness
  • Sociability

Other short-term effects include:

  • Using cannabis before driving doubles the risk of being involved in a motor vehicle accident
  • Decreased cognitive ability (e.g. decreased learning, memory and attention). These effects are reversible if user stops or greatly reduces their consumption
  • Some people who have tried cannabis find the effects unpleasurable. For example, they don’t like feeling disinhibited or experiencing distorted time and space perception, they become more anxious, less talkative, more fearful, more withdrawn and/or more paranoid.
Long-term effects

Several consequences of long-term regular cannabis use have been identified. They include:

  • Increased risk of dependence (i.e. “addiction”). About 10 per cent of all cannabis users meet the criteria for dependence: 17 per cent of those who began using cannabis in adolescence meet the criteria for dependence. [2]
  • Increased risk of experiencing psychotic symptoms (e.g. hallucinations, delusions) or psychotic disorders (e.g. schizophrenia).
  • Increased risk of acute episodes of chronic bronchitis for cannabis smokers

How can a person reduce the risks associated with cannabis use?

If you decide to use cannabis, there are ways to reduce the chance you will experience immediate or long-term negative consequences.

Canada’s Lower-Risk Cannabis Use Guidelines, developed by the Centre for Addiction and Mental Health, lists 10 harm reduction strategies. These strategies are "based on the best available scientific evidence". They are:

"1. Remember that every form of cannabis use poses risks to your health. The only way to completely avoid these risks is by choosing not to use cannabis. If you decide to use cannabis, follow these recommendations to lower risks to your health.

2. The earlier in life you begin using cannabis, the higher your risk of serious health problems. Teenagers, particularly those younger than 16, should delay using cannabis for as long as possible. You’ll lower your risk of cannabis-related health problems if you choose to start using cannabis later in life.

3. Higher-strength or more powerful cannabis products are worse for your health. If you use products with high tetrahydrocannabinol (THC) content, the main mind-altering ingredient in cannabis, you’re more likely to develop severe problems, such as dependence or mental health problems. Cannabidiol (CBD), another cannabis ingredient, can counteract some of THC’s psychoactive effects. If you use, choose low-strength products, such as those with a lower THC content or a higher ratio of CBD to THC.

4. Don’t use synthetic cannabis products. Compared with natural cannabis products, most synthetic cannabis products are stronger and more dangerous. K2 and Spice are examples of synthetic cannabis products. Using these can lead to severe health problems, such as seizures, irregular heartbeat, hallucinations and in rare cases, death.

5. Smoking cannabis (for example, smoking a joint) is the most harmful way of using cannabis because it directly affects your lungs. There are safer, non-smoking options like vaping or taking edibles that are better for your lungs. Keep in mind that these alternatives aren’t risk-free either.

6. If you choose to smoke cannabis, avoid inhaling deeply or holding your breath.
These practices increase the amount of toxins absorbed by your lungs and the rest of your body, and can lead to lung problems.

7. The more frequently you use cannabis, the more likely you are to develop health problems, especially if you use on a daily or near-daily basis. Limiting your cannabis use to occasional use at most, such as only using once a week or on weekends, is a good way to reduce your health risks. Try to limit your use as much as possible.

8. Cannabis use impairs your ability to drive a car or operate other machinery. Don’t engage in these activities after using cannabis, or while you still feel affected by cannabis in any way. These effects typically last at least six hours, but could be longer, depending on the person and the product used. Using cannabis and alcohol together further increases your impairment. Avoid this combination before driving or operating machinery.

9. Some people are more likely to develop problems from cannabis use.  Specifically, people with a personal or family history of psychosis or substance use problems, and pregnant women should not use cannabis at all.

10. Avoid combining any of the risky behaviours described above. The more risks you take, the greater the chances of harming your health as a result of cannabis use."


The High-Way Code: The guide to safer, more enjoyable drug use (cannabis) is “The first guide to safer drug use voted for by people who take drugs”.  The guide was developed from a survey of over 38,000 cannabis users who were asked about the strategies they use to reduce the risk of harm when using cannabis.  The strategies include:

  • Use a vaporizer
  • Avoid driving and cycling
  • Avoid using during the day
  • Set limits on amount used
  • Have 3-4 week breaks
  • Eat cannabis
  • Avoid inhaling deeply

When does cannabis use become problematic?

Cannabis use can be problematic. This occurs when a person continues to use cannabis despite significant consequences or distress.

One way to identify if cannabis use is problematic is to complete a self-assessment such as the Cannabis Use Disorders Identification Test (CUDIT-R), which you can take here.

Another way to identify problematic cannabis use is to review the signs of cannabis dependence from the American Psychological Association and note how many apply to you:

  • Taking more cannabis than was intended or for a longer period than planned
  • Difficulty controlling or cutting down cannabis use despite having a strong desire to cut back on use
  • Spending a lot of time obtaining, using or recovering from cannabis use
  • Strong cravings or urges to use cannabis
  • Problems at work, school, and home as a result of cannabis use
  • Continuing to use cannabis after facing repeated or persistent issues with relationships that are caused or made worse by cannabis use
  • Giving up or reducing other activities in favor of cannabis
  • Taking cannabis in high-risk situations, such as driving
  • Continuing to use cannabis despite physical or psychological problems
  • Tolerance to cannabis (i.e. you need to use more cannabis to achieve the same effect)
  • Experiencing withdrawal when discontinuing cannabis or drastically reducing, which include anger, irritability, restlessness, sleeping difficulty/bad dreams, decreased appetite, headache and depression

Mild dependence: 2-3 signs
Moderate dependence: 4-5 signs
Severe dependence: 6 or more signs

Resources available at Concordia and the greater community

Where can I get help for problematic cannabis use?

If you identify that your cannabis use problematic and you want to stop using or reduce your harm by cutting down, consult the following resources:

At Concordia

Self-help resources:

Community Resources

  • Marijuana Anonymous Online meetings are held at many different times throughout the week: see their Online Meeting Schedule. You can also get support through their Chatroom 24/7.
  • Marijuana Anonymous meetings are held in-person several days of the week at different locations around Montreal [ON HOLD DURING PANDEMIC MEASURES]. Near to Concordia are the M.A. meetings at Chabad Lifeline (4615 Chemin de la Côte-S.-Catherine) and at St. James United Church (Thursday evenings at 7 p.m.; 463 Saint-Catherine St W, 514-288-9245).
  • CRD Foster provides addiction rehabilitation services for the Anglophone population
  • Le Centre Dollard Cormier provides addiction rehabilitation services for the Francophone population.
  • Le Portage Quebec provides a therapeutic community for addiction recovery
  • The Addictions Unit, Griffith Edwards Centre, McGill University Health Centre (MUHC) is a hospital-based addictions service that provides a continuum of care for adults (18 years of age or more) with drug/alcohol and mental health disorders.
  • SMART Recovery "offers an abundance of support options at your disposal to help you fight off addiction and maintain sobriety. SMART Recovery® Quebec offers weekly meetings in the Montreal NDG area open to the public looking for on-going support and help.  SMART Recovery is a non-profit organisation and offers its services for free".  They also have online access to meetings (for those who can't attend), an online message board, a "Tool Box" that contains worksheets and a section with "Articles and Essays".

Helpful Links


Frequently Asked Questions about Cannabis


[1] National Academics of Sciences, Engineering and Medicine, 2017, The health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research. Washington, D.C: The National Academics Press: doi: 10.17226/24625

[2] Volkow N.D., Baler R.D., Compton W.M. et Weiss S.R.B. (2014) Adverse health effects of marijuana use, The New England Journal of Medicine, vol. 370, p.2219-2227



Back to top Back to top

© Concordia University