Cannabis and Your Health

Weed (cannabis) is legal in Canada as of October 17, 2018. 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
  • The effects can last up to 8 hours or more

If you’re eating or drinking cannabis:

  • You’ll likely feel the effects within 30 minutes to 2 hours or more
  • The effects can 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 8 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.
  4. Avoid using too much, especially with edibles. When you eat/drink weed, it can take up to two hours to feel the full effects. Starting with a small amount and going slowly can help you avoid a “bad high” which may include confusion, paranoia, anxiety, hallucinations, fast heart rate, nausea or vomiting.
  5. Avoid high potency strains and products. The higher the THC content, the greater your risk for negative short-term and long-term problems. Dabbing and hash oil products can have very a high THC content. Products with a higher CBD content may reduce some of the negative effects.
  6. Be aware of quality. Illegal sources of cannabis may contain pesticides, heavy metals, mould or other drugs.
  7. Don’t use and drive. Cannabis impairs coordination, reaction time and other abilities needed to drive safely.
  8. 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.
  9. Avoid sharing joints or equipment that could spread infections.​

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 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.

Edibles are not available for legal purchase in Ontario at the current time.

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.
  • Wait until you feel the full effects before consuming more (this could take 2 hours or longer).
  • 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. (Best Start)
  • 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.

Breastfeeding is the healthiest choice for your baby. If you have questions about having a healthy pregnancy, breastfeeding or parenting, get in touch through Let’s Talk Parenting.

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 Let’s Talk Parenting.

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 31, 2018