Cannabis and your health

Test your cannabis health knowledge with our Interactive Cannabis Quiz or read on to learn more about cannabis and your health.


Cannabis (also known as marijuana, weed or pot) is a product of the plant Cannabis sativa. Cannabis contains over 400 different chemicals, including tetrahydrocannabinol [THC] and cannabidiol (CBD). THC is the active chemical responsible for the intoxicating effect (or “high”) that people may experience when they consume cannabis.

Cannabis became legal for non-medical use in Canada on October 17, 2018. In Ontario, you have to be 19 or older to legally buy, use, possess or grow cannabis.

Read on to find out more about the short- and long-term effects on your health and ways to help lower the risk of negative outcomes associated with cannabis use.

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 and the amount of the active ingredients, including THC and 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 cannabis:

  • 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 cannabis 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 affects people differently.

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 or substance use disorder.

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 symptoms of psychosis)

Long-term effects

Over time, if you continue to use cannabis, it can: 

  • Harm your lungs, if you smoke or vape 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 developing 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

Learn more about the health effects of cannabis.

Ways to reduce your risk

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

  • 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.
  • Minimize your risk when smoking or vaping. Cannabis smoke contains many of the same cancer-causing chemicals as tobacco smoke. Smoking cannabis regularly can harm your lungs and lead to respiratory issues such as coughing, wheezing, sore throat, chest tightness, lung infections and chronic bronchitis. Vaping can also damage the lungs and in some cases has been linked to Vaping-Associated Lung Illness (VALI), which is a serious medical condition causing inflammation of the lungs resulting in cough, shortness of breath and possible hospitalization. The long-term impacts of vaping are still unknown. To protect your lung health, it is safest to avoid smoking or vaping cannabis. If you choose to smoke or vape, learn about inhalation accessories and how to lower your risk when using them.
  • Avoid overconsuming, especially with edibles. With edibles 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 reduce the risk of negative effects.
  • Choose legal cannabis. Illegal sources of cannabis may contain pesticides, heavy metals, mould or other drugs. If you plan to use cannabis, get it from an authorized retailer in Canada. Legal cannabis is tested and quality controlled, so you know exactly what you are buying.
  • Don’t use and drive. Cannabis impairs coordination, reaction time and other abilities needed to drive safely. The amount of time the effects last can vary, so the best option is to plan a safe ride home.
  • 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.
  • 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.
  • Avoid sharing joints or other inhalation accessories that could spread infections.​
  • 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. It can also impact your ability to care for your child or respond to their needs. Choose a safe environment and make sure you are with someone you trust. 
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.

Safer use of edible cannabis products

Edibles” refers to cannabis products you eat or drink.

Consuming cannabis in a food or drink affects you differently than smoking or vaping.

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

It is possible to overconsume edibles. When this happens, you could experience symptoms of psychosis, become paranoid or anxious and experience other health effects.

How to reduce your risk when consuming edibles:

  • 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 cannabis, call your veterinarian.

Cannabis use during pregnancy and breastfeeding

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.

The chemicals in cannabis (including THC) pass into and build up in breastmilk. Cannabis may make your baby drowsy and it could make it harder for your baby to latch properly. It may also affect your baby’s movement and responses.

The safest option for you and your baby is to not use cannabis when you are pregnant or breastfeeding.

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


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. 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, you can connect with a public health nurse or access resources through our parenting supports.

Talking to your kids about cannabis

No matter how old your children are, you are their most important source of information about cannabis. Having open communication, providing a supportive environment, and utilizing available resources can help parents and caregivers address the topic of substance use with their children. Talk early, and talk often.

For more information and resources to help navigate conversations about cannabis use with children and youth, visit our Youth Substance Use page or watch our Cannabis and Other Drugs Parent Information Session video.

Visit Canada’s lower-risk cannabis use guidelines and our Cannabis Resources and Supports page for more.

If you would like to speak to someone about cannabis information or supports, please contact us at 1-800-265-7293 ext. 7006.