Cannabis and Your Health

Weed (cannabis) is now legal in Canada. In Ontario, you have to be 19 or older to legally buy, use, possess, or grow weed.

There are risks to using cannabis. Avoiding use is the only way to avoid the risks.

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What happens when you use cannabis

Cannabis (marijuana, weed) 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 or more
  • 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 weed can increase your risk for injuries and accidents.

Driving after using cannabis is dangerous and illegal. Learn more about driving and cannabis.

Health effects of cannabis

Cannabis (marijuana, weed) affects people differently. If you use cannabis, you might experience enjoyable, harmful or medicinal effects.

Using cannabis can affect your physical and mental health. It can also be addictive – both psychologically and physically.

The risks are higher if you start using cannabis at a young age (under 25) because the brain is still developing. The risks are also higher for those who have a personal or family history of mental illness.

Short-term effects

Cannabis can:

  • Slow your reaction time
  • Make you less coordinated
  • Make it harder to pay attention, learn and remember things
  • Affect your mood and mental health (e.g., cause panic, anxiety or trigger psychosis)

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 by:
    • Having the opposite effect than you’re hoping for (e.g., using to relieve stress/anxiety can make problem worse)
    • Increasing the risk of psychosis (e.g., losing touch with reality, hallucinations)
    • Increasing the risk of suicide, depression and some forms of anxiety (more research is still needed to better understand this)

Signs of problematic use include:

  • Use getting in the way of everyday life – like fulfilling duties at your job or participating in sports or other activities
  • Using more or longer than you planned
  • Not being able to cut down or control use

To learn more about cannabis or to get help:

Ways to reduce your risk

If you choose to use cannabis, here are some ways you can reduce the risk of health effects:

  1. 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.
  2. Reduce use. The more weed 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.
  3. 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.
    • Recent 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
  4. Avoid overconsuming, especially with edibles. With edibles it can take up to two hours to feel the effects and up to 4 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 reduce the risk of negative effects.
  5. Be aware of quality. Illegal sources of cannabis may contain pesticides, heavy metals, mould or other drugs.
  6. Don’t use and drive. Cannabis impairs coordination, reaction time and other abilities needed to drive safely.
  7. Don’t mix with alcohol or tobacco. Mixing with alcohol can increase impairment and negative reactions, and mixing with tobacco can lead to nicotine addiction and harm the lungs.
  8. Avoid high potency products. The higher the THC content, the greater the risk for negative outcomes. Using products with a lower amount of THC (e.g., less than 10% THC for products that are smoked/vaped and 2.5 mg of THC or less for products that are eaten) can help reduce the risk of negative effects. Certain cannabis extracts like hash, kief, wax or shatter contain a very high concentration of THC.
  9. Avoid sharing joints or equipment that could spread infections.​
  10. Avoid synthetic cannabis products, like K2 or Spice. These products have been linked to seizures, irregular heartbeat, panic attacks, and in some cases, death.
  11. Think about when and where you use it. Using weed 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. 

To learn more about cannabis or to get help:

Using cannabis for medical reasons

Some people use cannabis (weed) 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 weed or to get help:

Safer use of edibles

“Edibles” refers to cannabis (marijuana, weed) in a form that can be eaten or drunk.

When cannabis is consumed in a food or drink (rather than smoked or vaped), it affects you differently.

Edibles affect you differently than if you smoke or vape weed.

  • When smoking or vaping, you might feel the effects within seconds to minutes.
  • When eating or drinking products made with weed, it can take up to two hours or more to feel the effects and up to 4 hours to feel the full effects.

It is possible to eat/drink too much weed. 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 are 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 4 hours).
  • Keep edibles in a secure (locked) location, out of reach from children, teens and pets, where they aren’t visible.
  • If you think your child ate cannabis, get medical help right away. Call the Ontario Poison Centre at 1-800-268-9017 or seek medical attention right away. Call 911 immediately if your child seems ill, has difficulty breathing or if you are worried for other reasons. 
  • If a pet eats weed, call your veterinarian.

To learn more about cannabis or to get help:

Cannabis use during pregnancy

When you’re pregnant, what you put in your body is shared with your baby. Cannabis is legal, but that doesn’t mean it’s safe to use during pregnancy or while breastfeeding.

In fact, no form of cannabis, including extract, oil, pills, or oils/creams put on your skin, is known to be safe during pregnancy.

Using cannabis during pregnancy may have harmful effects on mom and baby during pregnancy (such as preterm labour, low birthweight). It may also affect a child’s brain during childhood and into adulthood.

Talk to your doctor about safer treatments for morning sickness and managing pain when pregnant.

To learn more about cannabis or to get help:

Cannabis use while breastfeeding

The chemicals in cannabis (including THC) pass into and build up in breastmilk.

No form of cannabis (weed, marijuana), including extracts, oil, pills, or oils/creams put on your skin, is known to be safe during pregnancy or breastfeeding.

There is some scientific evidence that when a breastfeeding mother uses cannabis it can slow baby’s motor development (movement and responses). More research is needed, but the safest option for you and your baby is to not use cannabis during the time you’re breastfeeding.

For more information about cannabis and breastfeeding:

Cannabis use while parenting

Using cannabis while parenting affects how you interact with your child.

It affects your mood and judgement, and your ability to respond to your baby’s/child’s needs.

If you choose to use cannabis, make sure there is another adult available who isn’t using cannabis to take care of your child, and avoid exposing children to second-hand cannabis smoke. Second-hand cannabis smoke can affect children’s alertness, understanding and judgement.

Keep cannabis in all forms in a secure (locked) location, out of reach from children, teens and pets, where they aren’t visible.

If you think your child ate cannabis, get medical help right away. Call the Ontario Poison Centre at 1-800-268-9017 or seek medical attention right away. Call 911 immediately if your child seems ill, has difficulty breathing or if you are worried for other reasons.

If you have questions about having a healthy pregnancy, breastfeeding or parenting, get in touch through the Client and Community Support line.

For more information about cannabis and parenting visit:

Talking to your kids about cannabis

Cannabis (marijuana, weed) is legal in Ontario for adults ages 19 and older as of October 17, 2018.

No matter how old your children are, you are their most important source of information about cannabis. Talk early, talk often.

Cannabis affects young people differently.

  • Cannabis can be addictive (both psychologically and physically), and the risk is higher if you start using at a young age.
  • Signs of addiction include:
    • Use getting in the way of everyday life, like going to school, fulfilling duties at a job or participating in sports or other activities
    • Using more or longer than planned
    • Not being able to cut down or control use
  • 1 in 6 who start using cannabis as teens get addicted. The risk is higher (1 in 2) for those who use every day.
  • Regular cannabis use before the brain is fully developed (about age 25) can affect memory, thinking and attention.
  • The risks associated with cannabis use, including mental health problems, dependence and lung conditions, are greater in young people.
  • This is especially true when:
    • Cannabis use begins in early adolescence
    • Use is frequent
    • Use continues over time
  • Some of these harms may never go away. 

Here are some of the facts you might want to share:

  • Cannabis affects judgement and reaction time. Driving impaired is illegal. 
  • Cannabis is more potent now than in the past.

How can you start the conversation?

This page was last updated: October 18, 2019