Health effects

How cannabis use affects health including mental health concerns, risks for pregnancy and breastfeeding and combining cannabis with other substances and medications.

What is cannabis?

Cannabis is a product of the cannabis plant. It contains over 100 chemicals called cannabinoids that affect the brain and body. The two best-known cannabinoids are:  

  • Tetrahydrocannabinol (THC) is responsible for the way the brain and body respond to cannabis and causes the intoxicating effects or feelings of ‘high’ of cannabis. The potency of cannabis depends on how much THC it contains. 

  • Cannabidiol (CBD) causes little to no intoxication or feelings of ‘high,’ but it can still have effects on the brain. 

Cannabis comes in many forms, including dried cannabis, cannabis extracts, cannabis topicals and edible cannabis (cannabis-infused food and drinks).

Cannabis can be used to make a wide range of products that are different in: appearance and consistency, taste and smell, amount of THC (tetrahydrocannabinol), amount of CBD (cannabidiol) and how they are used (i.e., inhaled, ingested). 

How cannabis use affects health

There are short-term and long-term health effects and risks associated with cannabis use, particularly for persons under the age of 25, during pregnancy and while breastfeeding, and for persons living with or with a family history of mental illness. 

Everyone's response to cannabis is different. It depends on age, pre-existing medical conditions, how much is used, how often and how long cannabis has been used before. A person’s response also depends on where it is being used, whether food, alcohol, other drugs, or health products have been consumed, the amount of THC (tetrahydrocannabinol) and CBD (cannabidiol) in the product, and how it has been consumed.

If you smoke, vape or inhale cannabis, the effects can be felt almost immediately. If you consume cannabis as a food or a drink, the effects may be more delayed and can last longer.

A person’s response to cannabis can also be different from one time to the next.

The physical effects of cannabis may include:

  • red eyes
  • dry mouth and throat
  • irritated respiratory system (from smoking) e.g., sore throat, hoarse voice, coughing, wheezing, tightness in chest 
  • increases in appetite and heart rate
  • decreases in blood pressure, balance, and stability
  • drowsiness or restlessness, depending on the amount taken and a person’s individual response to the drug.

Cannabis use can affect everyone’s health differently. A person’s level of risk depends on the factors, such as: 

  1. Strength (THC) of cannabis product Example: Using higher strength (20% THC [200 mg/g] or more) cannabis products 
  2. Frequency and duration of use Example: Using cannabis daily or almost daily and over a long period of time (several months or years)
  3. Method of use Example: Smoking cannabis can increase the risk of breathing problems and long-term conditions
  4. Age of first use Example: Starting to use cannabis regularly before the age of 25 (before the brain has fully developed) 
  5. Personal history of mental health conditions Example: Using cannabis while experiencing depression or anxiety 
  6. Family history of mental health conditions Example: Using cannabis when there is a family history of psychosis, schizophrenia, or addiction to other substances 

These health effects and risks are possible for anyone who uses cannabis: 

  • impairment, which can lead to serious injuries or death, including those from car accidents and operating equipment 
  • problems with physical co-ordination and reaction time
  • problems with thinking, memory, concentration, and ability to make decisions
  • hallucinations, such as seeing, hearing, tasting, smelling, or feeling things that do not really exist 
  • changes in mood and feelings - fear, or panic
  • developing or worsening mental health problems – depression, anxiety disorders, suicidal behaviours, and psychosis - including triggering a psychotic episode in some people
  • permanent harm to mental functioning
  • interference with brain development and long-lasting damage to the brain - especially if cannabis use starts at an early age (i.e., under 25 years) before the brain has fully developed  
  • breathing and lung problems from smoking cannabis (i.e., bronchitis, lung infections, long-term cough, increased mucus buildup in the chest)
  • cancer from smoking cannabis 
  • problems during or after pregnancy, especially if cannabis is smoked
  • tolerance to the effects of cannabis - accustomed to a particular dose and higher amounts are needed to obtain the same effects 
  • cannabis dependence (Or addiction, cannabis use disorder, or problematic cannabis use) - a treatable medical condition that affects the brain and involves compulsive and continuous use despite negative impacts to a person, their family, friends, and others


Pregnancy and Breastfeeding

There is no known safe amount of cannabis use during pregnancy or breastfeeding. The effects of cannabis can be passed on to a baby during pregnancy or while breastfeeding. Some of these effects can last the child’s lifetime. 

The compounds and toxins in cannabis are passed through the blood to the unborn baby and through breast milk.  

Cannabis in all forms, and no matter how it is used, can affect a baby’s growth and brain development. Cannabis use during pregnancy can lead to babies being born too small and too early.  As a baby grows, their brain goes through many changes that can be altered by cannabis. It can also interfere with their attention, memory, and reasoning abilities, behaviour and processing of emotions, and problem-solving skills. 

Being exposed to cannabis during pregnancy and breastfeeding can increase a child’s risk of: 

  • Hyperactivity 
  • Impulsive behaviours  
  • Sleep disorders
  • Future substance use 

Not using cannabis or CBD (cannabidiol) during pregnancy or when breastfeeding is the safest option for you and the baby. If you are, or are thinking about, using cannabis during pregnancy to manage nausea, anxiety, or pain, consider speaking with a health care provider to discuss your situation and to explore your options. There are other safe and effective options that can help. 

Pregnancy and cannabis

Society of Obstetricians and Gynaecologists of Canada

Is it OK to use cannabis during pregnancy and while breastfeeding?

Canadian Centre on Substance Use and Addiction (PDF)

Combining cannabis with other substances

Using cannabis with other substances, including alcohol, opioids, cocaine, prescribed or over-the-counter medications, can lead to negative health effects, increased risk of harm and be dangerous.  

Be aware of what happen when mixing cannabis with other substances.

Consuming cannabis with alcohol increases the level of impairment, risk of over-intoxication and the risk of injury or death. 

Smoking cannabis with tobacco increases exposure to chemicals that can increase the risk of developing lung and heart disease.  Using cannabis with tobacco can increase the risk for dependence on these substances more than smoking either one alone. 

Combining cannabis with other substances such as cocaine, opioids, heroin, etc. can increase a drug’s effects, and lead to interactions that can be dangerous. 

Cannabis can interact with medications and have a negative effect on health.

Medications that can interact with cannabis include: 

  • Pain medications  
  • Heart medications and blood thinners
  • Sleeping pills 
  • Anti-depressants and anti-anxiety medications 
  • Antibiotic and antifungal medications  
  • Allergy, cold and flu medications 
  • Heartburn medications 
  • Anti-seizure medications 
  • ADHD medications 
  • Drugs to treat HIV/AIDS 

Cannabis and your medication

Canadian Centre on Substance Use and Addiction (PDF)

Cannabis and other substances

Canadian Centre on Substance Use and Addiction (PDF)