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Just as with alcohol or tobacco, cannabis is not a harmless substance. It’s important for you to be informed of what is known about the harms of cannabis use so you can reduce your health risks.

Cannabis use can cause unpleasant, unwanted or negative effects on your brain and body, including:

  • confusion and difficulty concentrating,
  • anxiety, fear or panic,
  • psychotic episodes of paranoia, delusions or hallucinations,
  • poor co-ordination and slow reaction time,
  • increased risk of injury (e.g., motor vehicle collision, falls),
  • sleepiness,
  • coughing, wheezing,
  • shortness of breath,
  • decreased blood pressure (risk of fainting or passing out),
  • increased heart rate (increased risk of heart attack), or
  • hyperemesis syndrome (uncontrollable vomiting).

Long-term effects develop over time with daily or near-daily use over weeks, months or years. The effects can last from several days to months or longer after you stop using cannabis. For those who begin consuming cannabis at a young age (i.e. under 25) or use often, the following effects may become permanent:

  • addiction (Cannabis Use Disorder),
  • depression or anxiety,
  • schizophrenia or other psychosis,
  • harms to memory and concentration,
  • lowering of intelligence or IQ,
  • negative effects on your ability to think and make decisions,
  • chronic (long-term) cough (when smoked),
  • increased mucus buildup in the throat (when smoked),
  • bronchitis (when smoked), or
  • lung infections (when smoked).

People can become addicted to cannabis. About 1 in 6 teenagers and 1 in 11 adults who use cannabis will develop an addiction.

Regular, often (daily) and heavy cannabis use can lead to a Cannabis Use Disorder, physical dependency, and addiction. The THC in cannabis causes an increase in levels of dopamine, the pleasure chemical in the brain, which can motivate people to keep using it. When you stop using cannabis, you can also get withdrawal symptoms that make you use it again for relief, such as:

  • irritability,
  • trouble sleeping,
  • dysphoria - state of generalized unhappiness, restlessness, dissatisfaction, or frustration,
  • depression or anxiety,
  • cravings, or
  • changes in appetite and weight loss.

While overdose of cannabis does not happen in the same way as things like opioids, there is still a risk of consuming too much and having a bad reaction such as high levels of anxiety, fear or panic, and psychotic episodes of paranoia, delusions or hallucinations. Hyperemesis syndrome may also occur, where consuming cannabis triggers uncontrollable vomiting.

Overdose or poisoning from other substances: When cannabis is purchased from an unregulated supplier (i.e., off the street or black market), you have no guarantee of what you are getting and the cannabis could contain other substances such as opioids, cocaine, methamphetamine, MDMA, LSD, or household chemicals.

For the reasons above, you should always “start low and go slow” with your cannabis consumption, and always purchase from a licensed retailer.

Overdose in children: If cannabis is stored in areas that can be accessed by children, the possibility of them either intentionally or unintentionally consuming the product is increased. Similar to alcohol, it is important that products that can cause impairment, overdose, or poisoning are stored out of reach from children.

If you or someone else is having a bad reaction to cannabis, or a child ingests cannabis, call the Ontario Poison Centre (1-800-268-9017) or 911 immediately.

Youth and young adults under age 25 who use cannabis are at higher risk of effects on brain development and function that may become permanent. This is because the brain continues to develop until the age of 25 and the THC in cannabis affects the same areas in the brain that direct development.

Young people who use cannabis are at higher risk of:

  • mental illness (depression, anxiety, schizophrenia or other psychosis),
  • addiction to cannabis,
  • problems with memory, thinking, learning, problem-solving skills,
  • behavioural issues,
  • difficulties with relationships at home, school or work, and
  • lung and respiratory problems from smoking cannabis.

Young people who use cannabis may be tempted to use it with other substances such as alcohol, which intensifies the effects and can lead to more health risks and worsening judgment leading to reckless behavior (such as driving while impaired, having unprotected sex, or other risk-taking behaviors).

For more information: Cannabis: What Parents/Guardians and Caregivers Need to Know

There is NO known safe amount of cannabis use while pregnant or breastfeeding regardless of how it is used (smoked, vaped, eaten, taken as a pill, applied as a cream).

The chemical THC in cannabis is passed on to your baby during pregnancy and when breastfeeding.
While more research is needed, studies have shown that cannabis use during pregnancy poses risks to babies and children and may have long-term effects on teens and young adults. Some of these risks include:

Babies:

  • lower birth weight,
  • increased risk of Neonatal Intensive Care Unit (NICU) admission ,
  • increased startles and tremors (e.g., shaking), and
  • changes in sleep patterns.

Children:

  • poorer attention (e.g., easily distracted),
  • poorer memory,
  • behaviour issues,
  • difficulties in school, and
  • mental health concerns (e.g., symptoms of depression).

Teens and Young Adults:

  • increased risk of behavioural problems,
  • poorer school performance, and
  • more likely to start trying and using cannabis or other substances (e.g., tobacco, alcohol) at an earlier age.

The safest option for you and your baby is to NOT use cannabis while pregnant or breastfeeding.

Although edibles will not be legal at the same time as cannabis is legalized in Canada, here are some things you should know:

  • The effects of cannabis from eating an edible product can be delayed up to 2 hours. If you don’t wait 2 hours to feel the effects, you may consume larger amounts and have worse impairment when you finally do feel it.
  • When ingesting edibles, the “start low and go slow” caution still applies as it will be hard to know how it will affect you.
  • Keep all cannabis products in child-resistant packaging and in a locked area. Keep it out of sight and reach from children.
  • Cannabis in food products are very dangerous to children. Children may mistake these products for regular food such as brownies and cookies and eat them.
  • If a child eats cannabis they can become very sick. Get medical help right away.

If your child ingests cannabis, call the Ontario Poison Centre (1-800-268-9017) or 911 immediately.

Cannabis smoke has many similar carcinogens, toxins, and irritants that are found in tobacco smoke and known to cause cancer, heart disease and respiratory diseases like bronchitis.

Cannabis is not harmless just because it’s more “natural”. Any substance, whether it’s tobacco, alcohol, or cannabis, will have effects on your mental and physical health, so it’s important to know what those are.

Although the risks from exposure to second-hand cannabis smoke are still being studied, cannabis smoke has many similar carcinogens, toxins, and irritants that are found in tobacco smoke and known to cause cancer, heart disease and respiratory diseases like bronchitis. For this reason, exposure to cannabis smoke should be avoided. Cannabis should not be smoked indoors and should be kept away from children.