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What you should know to make decisions about cannabis.

Source: Health Services

Note: While cannabis is legal in Canada, the Cannabis Regulation Act sets out certain restrictions in Quebec, notably for educational institutions like Concordia University, where the use of cannabis is not permitted.

Rules and Regulations Regarding Cannabis on Campus

About cannabis

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 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.


The effects of cannabis

What are the effects of cannabis?

Source: The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research (2017)

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 
  • The 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. (Source)
  • 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

Reducing the risks associated with cannabis

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


Problematic cannabis use

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).

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


If you identify that your cannabis use problematic and you want to stop using or reduce your harm by cutting down, consult addiction and substance-use resources for information, services and resources.

Frequently asked questions

The limited research on second-hand cannabis smoke has identified the following effects on people who have passively inhaled it:

  • They have detectable levels of THC in their blood.
  • They have detectable THC metabolites (by products of THC breakdown) in their urine.
  • Some have reported psychoactive effects (i.e. the “high”) from second-hand cannabis smoke; however, these effects were weaker than in active smokers.

The magnitude of the effects depends on a variety of factors that include:

  • If exposure occurred in a ventilated or unventilated environment
  • Air volume (how big the space is)
  • How many people were in the area and inhaled the smoke
  • The THC content of the cannabis
  • How many joints were lit
  • The number of people smoking cannabis

Therefore, someone in a small, enclosed room where several people are smoking joints may have detectable levels of THC in their blood and urine and may experience psychoactive effects, while someone who is walking past a person smoking a joint on the street will not be affected by second-hand cannabis smoke.

Both alcohol and cannabis are drugs that affect the central nervous system. Several risks of using them together have been identified:

  • A person may use more of each substance without realizing it, which increases their level of intoxication and the risks of experiencing negative consequences. Being very intoxicated makes a person less aware of their surroundings and they may find themselves in a dangerous situation.
  • Consuming alcohol before using cannabis increases the amount of THC that is absorbed. This can increase the risk of experiencing psychotic symptoms (e.g. paranoia), anxiety, terror or panic.
  • A person may be unable to vomit or they may choke on their vomit. When a person consumes too much alcohol, the body tries to eliminate the alcohol in the stomach by vomiting. Cannabis is an antiemetic: it prevents vomiting. If a drunken person cannot vomit, the alcohol remains in their stomach and will be absorbed into their bloodstream, which can lead to severe illness and even death. In addition, if a person cannot vomit properly they may choke on their vomit.
  • A person is more likely to “green out." “Greening out” is a term that refers to a negative experience with cannabis where a person feels sick (e.g. nausea, dizziness, sweaty, turn pale) and may vomit. This is not a common experience when using cannabis alone; it is, however, more likely to occur if alcohol is consumed before using cannabis.

A drug is a substance that changes the way the body works physically or psychologically. All drugs, including cannabis, have potential negative effects (i.e. risks). As such, there is no “safe” level of cannabis use or safe age to begin using cannabis. If a person chooses to use cannabis, they should take steps to reduce the risks associated with its use.

The evidence-based Low-Risk Cannabis Use Guidelines state that 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.”

The reason to delay use until later in life is because the human brain continues to develop until early adulthood. Some studies have found that cannabis use can disrupt the development of the brain and lead to mental health and other problems.

The effects that cannabis has on the developing brain depend on the amount used, the frequency of use, the concentration of THC, and individual factors.

Consuming cannabis has physical and cognitive effects that can impair a person’s ability to drive. These include a slower reaction time, difficulty staying focused, impaired decision making and changes in time and space perception. Driving under the influence of cannabis increases the risk of being involved in an accident. The risk increases as concentrations of THC in the blood increase.

Unlike alcohol, where blood alcohol concentrations can be calculated, there is no way for a person to calculate the concentration of THC in their blood to determine if their level of intoxication puts them at increased risk for an accident. Factors such as potency of THC, how much is used, the method of use, the frequency of use, time passed since last use and personal factors, affect blood THC concentrations.

The evidence-based Canada’s Lower-Risk Cannabis Use Guidelines recommend that you not drive a car or operate other machinery “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.”

Quebec has adopted a “zero drug tolerance” policy for driving under the influence of cannabis. Any level of THC detected in tests constitutes a legal offense.

If you are going to use cannabis for the first time, here are some things to consider:

  • Choose not to use if you are at increased risk for experiencing cannabis-related problems. Risks include:
    • You have a mental health condition (e.g. depression, schizophrenia)
    • There is a history of psychosis in your family
    • You are pregnant
    • You will be driving or operating machinery within the next 6 hours
  • Be clear about why you are choosing to try cannabis. Some people think that using cannabis will help manage negative feelings (e.g. stress, anxiety). Using cannabis may not help and it may even make a person feel worse. There are effective strategies for managing negative feelings, such as cognitive therapy. Pressure from friends or a romantic partner, and “because it is legal so why not?” are not good reasons to begin using cannabis.
  • Know what to expect. Cannabis affects people in different ways that depend on:
    • Personal factors (e.g. personality, family history, physical and mental health status, size etc.)
    • The situation in which cannabis is used
      • the type of cannabis used (e.g. THC concentration, THC to CBD ratio, indica vs. sativa)
    • The amount used
    • The method of use
  • Become informed about the effects that you may experience. The effects are more intense at first and start to fade over the course of a few hours.
    • The psychological aspects of being high include feelings of euphoria or happiness, increased social interest, losing track of time, becoming deeply fascinated in seemingly trivial things around you, as well as increased laughter or giggling.
    • Being high also has physical effects. These include increased heart rate, blood-shot eyes, dry mouth, and an increase in appetite (“the munchies”).
    • In general, consuming cannabis for the first time will leave you feeling relaxed and happy, however; in certain people, marijuana can cause paranoiaanxiety, or other unpleasant feelings.
  • Become familiar with the different ways to consume cannabis (e.g. smoking, vaping).
  • Check your mood. Using while in a bad frame of mind can intensify negative feelings and lead to a bad experience. Use when in a neutral or good mood.
  • Choose a lower risk method. Vaping is the least harmful to your lungs. A vaporizer does not burn the cannabis, so there is no smoke, which can be harsh on the lungs. Smoking (e.g. bong, pipe, joint) can be harsh on the lungs. Avoid joints that are rolled with tobacco as they can make a non-smoker feel dizzy and there is a greater chance of irritating the respiratory tract and coughing.
  • Take it SLOW. Regardless of which method you choose to use…GO SLOW. Use a small amount at first and wait to see how it affects you. Take a small puff and see how you feel. After 20 minutes if you would like to heighten the effects, take another small puff.
  • Try with a friend. Don’t try for the first time alone. If possible, try with a friend who has experience with cannabis.
  • Use in a safe environment. Avoid using in an unfamiliar environment. Choose one that is comfortable, relaxing, and familiar.
  • Avoid consuming alcohol with cannabis. If you drink alcohol before using cannabis, the effects of cannabis are increased and you may experience "greening out" where you feel sick (e.g. nauseous, pale, dizzy, vomit) and want to lay down.
  • Know what to do if you use too much. If you begin to experience signs of using too much (e.g. paranoia, anxiety, increased heart rate, dry mouth, lost coordination and hallucinations) don’t panic. If you are with friends, let them know what is happening. Lay or sit down, close your eyes and try to relax. Drink fluids and eat food. Stay in a safe, comfortable environment. Symptoms are temporary and will usually decrease within 15 minutes to an hour. If your discomfort becomes so intense that you think you need medical attention, ask someone to take you to the emergency room or call 9-1-1. Do NOT try to drive yourself anywhere!
  • Other things to keep in mind
    • Keep cannabis in a safe place, out of reach from children.
    • First time users may want to try cannabis a few hours before going to bed.

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.  For more information on medical marijuana consult the following resources:

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