Cannabis (also known as weed, pot or marijuana) became legal in Canada on October 17, 2018. In Ontario, you have to be 19 or older to legally buy, use, possess or grow cannabis.
There are health risks to using cannabis, especially if you start using before age 25. It can affect your mental health, change the way you learn and remember things, and cause addiction.
There are legal risks too, because cannabis is still illegal to buy, use, possess and grow, if you are under 19.
If you are 21 or under, or are a new driver (G1, G2, M1, M2 license), it’s against the law to have any cannabis in your system while you’re driving. No matter how old you are, driving after using cannabis is illegal and dangerous.
If you choose to use cannabis, there are steps you can take to reduce your risk.
Explore:
- What happens when you use cannabis
- How cannabis affects your health
- Using cannabis for medical reasons
- Addiction
- Mental Health
- Learning and memory
- Ways to reduce your risk
- Edibles (food and drinks) made with cannabis
- When cannabis is a problem
- Where to get help
What happens when you use cannabis
Cannabis affects people differently. It might cause enjoyable, harmful or medicinal effects. These effects can change depending on the strain of cannabis as well as the amount of the active ingredients (including tetrahydrocannabinol [THC] and cannabidiol [CBD]).
The effects of cannabis can include:
- A sense of well-being
- Relaxation
- Feeling high (euphoria)
- Anxiety or panic
- Confusion
- Sleepiness
- Lowered blood pressure
- Increased heart rate
- Feeling hungry
- Dry mouth
If you’re smoking or vaping:
- You’ll likely feel the effects within seconds to minutes
- It can take up to 30 minutes to feel the full effects
- The effects can last up to 6 hours (and some remaining effects could last up to 24 hours)
If you’re eating or drinking cannabis:
- You’ll likely feel the effects within 30 minutes to 2 hours
- It can take up to 4 hours to feel the full effects
- The effects can last up to 12 hours (and some remaining effects could last up to 24 hours)
When you use cannabis, it affects your brain. It:
- Slows your reaction time
- Affects your judgement
- Makes you less coordinated
- Makes it harder to pay attention, make decisions and remember things
- May affect your mental health
Because of these effects, using cannabis can increase your risk for injuries and accidents.
Driving after using cannabis is dangerous and illegal. Learn more about driving and cannabis.
How cannabis affects your health
Cannabis can affect your physical and mental health.
Using cannabis regularly before the brain is fully developed (about age 25) can affect memory, thinking and attention. Some harms from using cannabis at a young age may never go away. This is especially true when:
- You start using cannabis as a teenager
- You use cannabis every day or almost every day
- You use cannabis for a long time
The risks of dependence (addiction), mental health issues and lung damage are also greater in young people.
Short-term effects
Besides affecting your reaction time, judgement, coordination and ability to make decisions, cannabis can:
- Affect your mood and mental health (e.g., cause confusion, panic, anxiety)
- Trigger psychosis (hearing and seeing things that aren’t really there)
- Decrease blood pressure, causing some people to faint
- Increase heart rate, which can be dangerous for those with heart conditions
Long-term effects
Over time, if you continue to use cannabis, it can:
- Harm your lungs, if you smoke it
- Make you physically or psychologically addicted
- Affect your mental health
- Affect your concentration, ability to learn things, and memory
Your risk of experiencing these effects is higher if you use cannabis daily or almost every day.
To learn more about cannabis or to get help:
Using cannabis for medical reasons
Some people use cannabis for medical reasons. If you want to use cannabis for a medical reason, talk to your healthcare provider. Cannabis might interact with medications or conditions you already have.
To learn more about cannabis or to get help:
Addiction
Cannabis can be both physically and psychologically addictive, especially if you start using at a young age.
- One in six people who start using as a teenager will develop addiction
- If you use every day, the risk can be as high as one in two
To reduce your risk of becoming addicted to cannabis:
- Delay use as long as possible, ideally until age 25
- Avoid using it every day or almost every day
It’s possible to be addicted to substances (such as cannabis, alcohol or tobacco) or activities such as gambling or technology. Any addiction can cause serious harm to your health, social life, school, work and financial future.
Signs of addiction include:
- Use getting in the way of everyday life, like going to school, working a job or participating in sports or other activities
- Using more or longer than planned
- Not being able to cut down or control use
To learn more about cannabis or to get help:
- Lower Risk Cannabis Use Guidelines for Youth
- Find resources and supports
- Cannabis: Important things to know (Kids Help Phone)
Mental health
Using cannabis can affect your physical and mental health. It can also be addictive—both psychologically and physically.
Using cannabis can:
- Have the opposite effect than you’re hoping for (e.g., using to relieve stress/anxiety can make the problem worse)
- Increase your risk of psychosis (e.g., losing touch with reality, hallucinations)
- Increase your risk of having a lifelong psychotic disorder, such as schizophrenia (risk is even higher if you have a personal or family history of psychosis)
- May increase your risk of suicide, depression and some forms of anxiety (more research is still needed to better understand this)
The mental health risks are higher if:
- You starting using cannabis at a young age (under 25) because the brain is still developing
- You use cannabis every day or almost every day
- You have a personal or family history of mental illness
To learn more about cannabis or to get help:
Learning and memory
If you use cannabis regularly, it can make it harder for you to learn, pay attention, make decisions and remember things. These effects can last for weeks after you stop using.
The brain is still developing until around the age of 25. The active ingredient in cannabis (THC) changes the system that directs brain development. We don’t yet know whether some of these changes are reversible or permanent.
To learn more about cannabis or to get help:
Ways to reduce your risk
No matter how you use cannabis, there are short-term and long-term health risks. The only way to avoid all of the risks is to not use it.
If you choose to use cannabis, there are safer ways of doing it. Here are some ways you can reduce your risk of harm:
- Delay use. The brain is still developing until age 25 and regular use before then increases risks of learning, addiction, and mental health issues. The greatest risk is for those using before the age of 16.
- Reduce use. The more cannabis you use (especially daily or almost every day), the higher the risk of problems with your health, education, and social life. Try to limit use to once a week at most.
- Avoid smoking. Smoking cannabis can harm your lungs. Vaping or edibles are safer for your lungs, but are not risk-free. If you smoke, avoid taking deep breaths or holding your breath. Some people believe these practices increase the high. There is not enough evidence to say whether or not that is true, but it is clear these practices increase the toxic chemicals that reach your lungs.
- There have been cases of severe lung-related illnesses linked to the use of vaping products have been reported in the United States. Most of these cases reported using vaping products with THC. Health Canada is warning Canadians of this potential risk and is advising people who use vaping products to monitor themselves for symptoms of lung illness (e.g., cough, shortness of breath, chest pain) and to seek medical attention if they have concerns. For more information, you can visit Health Canada’s website.
- Avoid using too much, especially with edibles. When you eat/drink cannabis, it can take up to two hours to feel the effects and up to four hours to feel the full effects. Starting with a small amount (e.g., 2.5 mg of THC or less) and waiting to feel the full effects before taking more can help you avoid a “bad high” which may include confusion, paranoia, anxiety, hallucinations, fast heart rate, nausea or vomiting.
- Avoid high potency products. The higher the THC content, the greater your risk for negative short-term and long-term problems. Using products with a lower amount of THC (e.g., less than 10% THC for products that are smoked/vaped, and 2.5mg of THC or less for products that are eaten) can help reduce the chance of negative effects. Dabbing and hash oil products can have a very high THC content.
- Think about your source. Illegal sources of cannabis may contain pesticides, heavy metals, mould or other drugs.
- Don’t use and drive. Cannabis does not make you a better driver. It makes you less coordinated and slows your reaction time. Plan a safe ride home.
- Don’t mix with alcohol or tobacco. Using cannabis at the same time as alcohol or other drugs can cause unpredictable effects (such as anxiety, vomiting or fainting) and increase your risk for accidents and injuries. Using cannabis with tobacco can lead to nicotine addiction and harm your lungs.
- Avoid synthetic cannabis products, like K2 or Spice. These products have been linked to seizures, irregular heartbeat, panic attacks, and in some cases, death.
- Think about when and where you use it. Using cannabis before school or work may affect your ability to learn or meet responsibilities or affect your safety. Choose a safe environment and make sure you are with someone you trust.
- Avoid sharing joints or equipment that could spread infections.
When to avoid cannabis
Sometimes not using is the best choice, like when:
- You or someone in your family has a history of psychosis (a mental state where people have trouble knowing what is real or not) or addiction (your chances of mental health problems and addiction are higher)
- You are pregnant or breastfeeding (cannabis can harm your baby)
If you have a bad reaction
If you have had too much or you are not enjoying your experience, try to keep calm until the effects wear off. Use with friends you trust, find a quiet safe space you feel comfortable in, stay with a friend, drink water and have something to eat.
If you or someone you’re with needs help, call:
- Ontario Poison centre (Poison Control) at 1-800-268-9017
- 911
To learn more about cannabis or to get help:
When cannabis is a problem
Signs someone is addicted to cannabis include:
- Use is getting in the way of everyday life – like paying attention in school, doing your job or participating in sports or other activities
- Using more or longer than planned
- Not being able to cut down or control use
Did you know that people who use cannabis are 2½ times more likely to gamble?
Many popular web or app-based games actually involve gambling. Gambling can lead to a variety of harms, including problems with your health, relationships, or finances. Many of the same factors that make people more likely to experience issues with drugs, also make people more likely to experience issues with mental health and gambling.
To learn more about the risks of gambling and gaming and to find support, check out:
Get help:
Edibles (food and drinks) made with cannabis
“Edibles” refers to cannabis in a form that can be eaten or drunk.
Edibles affect you differently than if you smoke or vape cannabis.
- When smoking or vaping, you might feel the effects within seconds to minutes.
- When eating or drinking products made with cannabis, it can take up to two hours to feel the effects and up to four hours to feel the full effects.
It is possible to eat/drink too much cannabis. When this happens, you could experience psychosis, become paranoid or anxious, and experience other health effects.
Planning to eat or drink a product made with cannabis?
- Do not mix cannabis in any form with alcohol. Mixing cannabis with alcohol can cause anxiety, nausea, vomiting or fainting. It can also increase the risk of accidents and injuries.
- Know how much is in a serving. If you’re new to edibles, look for products that contain 2.5 mg of THC or less to reduce risks and negative reactions.
- Wait until you feel the full effects before consuming more (this could take up to four hours).
- Keep edibles in a secure (locked) location, away from kids and pets.
- If a child eats cannabis, call the Ontario Poison Centre at 1-800-268-9017 or seek medical attention right away. If the child seems ill or has trouble breathing, or you are worried for other reasons, call 911.
- If a pet eats cannabis, call your veterinarian.
To learn more about cannabis or to get help:
Thank you to Gambling Research Exchange Ontario (GREO) for providing funding to this campaign through the BET: System Impact Grant, and also to the youth and community partners who contributed to this campaign.
This page was last updated: September 19, 2025