Cannabis and your health

Cannabis contains substances called cannabinoids that affect the brain and body. The 2 most well-known are THC (delta-9-tetrahydrocannabinol) and CBD (cannabidiol). THC causes the intoxicating and impairing effects of cannabis. CBD is not intoxicating and may reduce some of the effects of THC.

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The short-term effects of cannabis use

Everyone's response to cannabis may differ and can vary from one time to the next.
When cannabis is used, it can:

  • Impair your ability to drive safely or operate equipment
    • Cannabis can cause drowsiness, slow reaction times, lower your ability to pay attention and impair coordination. Footnote 1
    • Don't drive if you have consumed cannabis. Using cannabis and then driving can result in a car accident, serious injuries or death.
  • Make it harder to learn and remember things
    • Cannabis can impair your thinking, concentration, memory and decision-making, and can affect your ability to perform well on the job or at school.Footnote 2
  • Affect your mental health
    • Though cannabis can cause a high, it can also cause anxiety or panic.Footnote 2
    • In rare cases, cannabis can trigger a psychotic episode (not knowing what is real, experiencing paranoia, having disorganized thoughts and, in some cases, having hallucinations).Footnote 2

The long-term risks of cannabis use

Using cannabis frequently (daily or almost daily) and over a long time (several months or years) can:

  • Hurt your lungs and make it harder to breathe, if smoked
    • Cannabis smoke contains many of the same harmful chemicals found in tobacco smoke.Footnote 3
  • Affect your mental health
    • Frequent and prolonged consumption of THC increases the risk of dependence (also called addiction, problematic cannabis use or cannabis use disorder). It is also associated with an increased risk of developing or worsening disorders related to anxiety and depression.Footnote 4Footnote 5Footnote 6
    • Using products with higher levels of THC (for example, shatter, or wax) further increases the risk of mental health problems over time.Footnote 7Footnote 8Footnote 9
    • Stopping or reducing frequent cannabis use can improve your mental health.Footnote 5Footnote 10Footnote 22Footnote 23

The effects of cannabis on young people's health

Cannabis affects the same biological system in the brain that is responsible for brain development.Footnote 11

Youth and young adults are more likely to experience harms from cannabis because their brains develop until about age 25. The earlier you start consuming cannabis, the more harm it can do.Footnote 11

Starting as a teen, consuming frequently (daily or near daily) and consuming over a long time (several months or years) increases the risk of mental health problems. These problems include dependence and disorders related to anxiety and depression.Footnote 11

Frequent and prolonged use of cannabis can also harm important aspects of your thinking, like learning and memory. Stopping cannabis use can help improve these deficits. However, some of these harms may persist for months or years, or may not be fully reversible.Footnote 12 Footnote 13 Footnote 14

Lowering your risks when consuming cannabis

There are risks associated with cannabis use. The best way to protect your health is to completely avoid using cannabis or cannabis products.

If you choose to consume cannabis, there are ways to reduce the risk:

  • Use it in a safe and familiar environment and with people you trust, especially if you are inexperienced or a new user.
  • Delay cannabis use until the brain is fully developed. This occurs around the age of 25.
    • The earlier you begin using cannabis, the higher your risk of serious health issues, including dependence and other mental health problems.
  • Choose a product in which the amount of CBD is equal to or higher than the amount of THC.
    • The higher the THC content of a product, the more likely you are to experience adverse effects and greater levels of impairment. CBD may reduce some of the effects of THC.
  • If you smoke cannabis, avoid inhaling deeply or holding your breath.
  • Limit and reduce how often you use cannabis.
    • Frequent and prolonged use of cannabis can contribute to mental health problems over time. These include dependence, anxiety and depression.
  • Avoid mixing cannabis and other substances, like alcohol or opiates.
    • Using cannabis at the same time as drinking alcohol and/or using other drugs, such as pain medications (opioids) and tranquillizers (benzodiazepines) can cause more severe levels of impairment and adverse effects.
  • Avoid using cannabis and driving or using cannabis and operating other machinery.
    • After alcohol, cannabis is the substance most often linked to car accidents.
    • Cannabis can affect your concentration, attention and coordination, and slow your reaction time. Using it and driving or operating machinery increases the risk of having an accident, which can result in serious injuries or death.
  • Avoid using synthetic cannabis products, which are illegal.
    • Products known as synthetic cannabis (K2, spice) are not cannabis at all. These products are very different, have much stronger effects and are more dangerous than cannabis. Using synthetic cannabis can lead to severe health problems, such as seizures, irregular heartbeat, hallucinations and, in rare cases, death.
  • Avoid cannabis completely if you are:
    • pregnant or breastfeeding
    • at risk for mental health problems, especially
      • psychosis
      • schizophrenia
      • problematic substance use (addiction).

For more information, please refer to Lower-Risk Cannabis Use Guidelines.

The effects of cannabis on pregnancy and breastfeeding

Avoid cannabis completely if you are pregnant or breastfeeding. It can pose a risk to the fetus or newborn child. Cannabis can harm your baby.

There may also be other health risks associated with cannabis use during pregnancy and breastfeeding.Footnote 24Footnote 25

If you have questions, please contact your health care professional.

Cannabis for medical purposes

Some people use cannabis for their health problems. Deciding if cannabis is appropriate to treat your symptoms is best done in discussion with a health care provider.

To help you and your physician make informed decisions about the potential benefits and risks, we have published information on using cannabis for medical purposes.

Cannabis addiction

Using cannabis frequently can lead to addictionFootnote 15, also known as:

  • cannabis use disorder
  • cannabis dependence
  • problematic cannabis use

The risk of addiction to cannabis is lower than the risk of addiction to other substances, such as:

  • tobacco
  • alcohol
  • opioids

Nevertheless, experiencing a cannabis addiction can cause serious harm to your:

  • health
  • social life
  • school work
  • work and financial future

What we know:

  • Frequent cannabis use that starts in adolescence increases the chance of addiction.Footnote 16
  • Close to 1 in 10 adults who use cannabis will become addicted. This statistic rises to about 1 in 6 for people who started using cannabis as a teen.Footnote 16
  • Between 1/4 and 1/2 of all those who smoke cannabis daily will become addicted.Footnote 16

Quitting is not always easy. If you are struggling with your cannabis use, you can:

  • discuss your cannabis use with your physician or other trusted health care provider or counsellor
  • reach out to organizations or groups that deal with addiction

Know the signs of cannabis addiction and where to get help.

Cannabis poisoning

Accidentally consuming too much cannabis at one time can lead to adverse effects that are also known as cannabis poisoning. Cannabis poisoning is not generally known to be fatal. It can, however, be very unpleasant and potentially dangerous, sometimes requiring emergency medical attention and, in some cases, hospitalization. Children and pets are at greater risk of cannabis poisoning.

SymptomsFootnote 18Footnote 19Footnote 26 can include:

  • chest pain
  • rapid heartbeat
  • nausea and/or vomiting
  • psychotic episode
  • respiratory depression
  • severe anxiety and/or panic attack

The higher the THC content in a product, the higher the likelihood of experiencing adverse effects and/or poisoning, especially if you are a first-time or inexperienced user.

It is also easier to be poisoned by edibles or drinks when compared to smoking or vaping. This is because some of these products may be confused with similar non-cannabis products. It can also take much longer to feel the effects. The result is that people consume more before they feel the full effects and experience adverse effects or poisoning.

When eating or drinking cannabis, it can take up to:Footnote 15Footnote 17Footnote 18Footnote 19Footnote 20Footnote 21

  • 2 hours for you to start to feel the effects
  • 4 hours for you to feel the full effects
  • 12 hours for acute effects to subside

Store all cannabis products safely by keeping them out of reach of children, youth and pets. This is particularly important for edible cannabis, which may be mistaken for regular food or drinks.

If you've consumed cannabis and are experiencing particularly unpleasant or harmful effects:

  • stop using it
  • seek immediate medical attention or call your local poison control centre

Note: If you have consumed cannabis, don't drive. There is no guidance for drivers on:

  • how much cannabis can be consumed before it is unsafe to drive
  • how long a driver should wait to drive after consuming cannabis


Footnote 1

Hartman RL, Huestis MA. Cannabis effects on driving skills. Clin Chem 2013 Mar;59(3):478-92.

Return to footnote 1 referrer

World Health Organization (WHO). The health and social effects of nonmedical cannabis use.

World Health Organization (WHO). The health and social effects of nonmedical cannabis use.

Return to footnote 2 referrer

Footnote 3

Martinasek MP, McGrogan JB, Maysonet A. A systematic review of the respiratory effects of inhalational marijuana. Respir Care 2016 Nov;61(11):1543-51.

Return to footnote 3 referrer

Footnote 4

Gobbi, G., Atkin, T., Zytynski, T., Wang, S., Askari, S., Boruff, J.,... & Mayo, N. (2019). Association of cannabis use in adolescence and risk of depression, anxiety, and suicidality in young adulthood: a systematic review and meta-analysis. JAMA psychiatry.

Return to footnote 4 referrer

Footnote 5

Mammen, G., Rueda, S., Roerecke, M., Bonato, S., Lev-Ran, S., & Rehm, J. (2018). Association of Cannabis With Long-Term Clinical Symptoms in Anxiety and Mood Disorders: A Systematic Review of Prospective Studies. The Journal of clinical psychiatry, 79(4).

Return to footnote 5 referrer

Footnote 6

Gorelick, S. A., & Hermann, R. (2017). Cannabis use and disorder: Epidemiology, comorbidity, health consequences, and medico-legal status. UpToDate. September, 2-150.

Return to footnote 6 referrer

Footnote 7

Pierre, J. M. (2017). Risks of increasingly potent Cannabis: the joint effects of potency and frequency: as THC levels rise, the risk of psychosis, cognitive deficits, and structural brain changes increases. Current Psychiatry, 16(2), 14-21

Return to footnote 7 referrer

Footnote 8

Meier MH. Associations between butane hash oil use and cannabis-related problems. Drug and Alcohol Dependence. 2017;179:25-31.

Return to footnote 8 referrer

Footnote 9

Freeman, T. P., & Winstock, A. R. (2015). Examining the profile of high-potency cannabis and its association with severity of cannabis dependence. Psychological medicine, 45(15), 3181-3189.

Return to footnote 9 referrer

Footnote 10

Moitra, E., Anderson, B. J., & Stein, M. D. (2016). Reductions in cannabis use are associated with mood improvement in female emerging adults. Depression and anxiety, 33(4), 332-338.

Return to footnote 10 referrer

Footnote 11

Chadwick B, Miller ML, Hurd YL. Cannabis use during adolescent development: Susceptibility to psychiatric illness. Front Psychiatry 2013 Oct 14;4:129.

Return to footnote 11 referrer

Footnote 12

Rathee, S., & Shyam, R. (2018). Effect of Abstinence on Memory Functions in Cannabis Users. Journal of Psychosocial Research, 13(2), 443-451.

Return to footnote 12 referrer

Footnote 13

Schuster, R. M., Gilman, J., Schoenfeld, D., Evenden, J., Hareli, M., Ulysse, C.,... & Evins, A. E. (2018). One Month of Cannabis Abstinence in Adolescents and Young Adults Is Associated With Improved Memory. The Journal of clinical psychiatry, 79(6).

Return to footnote 13 referrer

Footnote 14

Meier, M. H., Caspi, A., Ambler, A., Harrington, H., Houts, R., Keefe, R. S.,... & Moffitt, T. E. (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences, 109(40), E2657-E2664.

Return to footnote 14 referrer

Footnote 15

National Academies of Sciences, Engineering, and Medicine. The health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research. Washington, D.C.: National Academies Press; 2017.

Return to footnote 15 referrer

Footnote 16

Volkow ND, Baler RD, Compton WM, Weiss SR. Adverse health effects of marijuana use. N Engl J Med 2014 Jun 5;370(23):2219-27.

Return to footnote 16 referrer

Footnote 17

Kosa, K. M., Giombi, K. C., Rains, C. B., & Cates, S. C. (2017). Consumer use and understanding of labelling information on edible marijuana products sold for recreational use in the states of Colorado and Washington. International Journal of Drug Policy, 43, 57-66.

Return to footnote 17 referrer

Footnote 18

Hudak, M., Severn, D., & Nordstrom, K. (2015). Edible cannabis-induced psychosis: intoxication and beyond. American Journal of Psychiatry, 172(9), 911-912.

Return to footnote 18 referrer

Footnote 19

Cone, E.J., Johnson, R.E., Paul, B.D., Mell, L.D., Mitchell, J., 1988. Marijuana-laced brownies: behavioral effects, physiologic effects, and urinalysis in humans following ingestion. J. Anal. Toxicol. 12, 169-175

Return to footnote 19 referrer

Footnote 20

Barrus DG, Capogrossi KL, Cates SC, Gourdet CK, Peiper NC, Novak SP, Lefever TW, Wiley JL (2016). Tasty THC: Promises and Challenges of Cannabis Edibles. Methods Rep RTI Press. 2016 Nov;2016. doi: 10.3768/rtipress.2016.op.0035.1611.

Return to footnote 20 referrer

Footnote 21

Chen, P., & Rogers, M. A. (2019). Opportunities and Challenges in Developing Orally-Administered Cannabis Edibles. Current Opinion in Food Science.

Return to footnote 21 referrer

Footnote 22

Schoeler T, Petros N, Di Forti M, Klamerus E, Foglia E, Ajnakina O, Gayer-Anderson C, Colizzi M, Quattrone D, Behlke I, Shetty S, McGuire P, David AS, Murray R, Bhattacharyya S (2016). Effects of continuation, frequency, and type of cannabis use on relapse in the first 2 years after onset of psychosis: an observational study. Lancet Psychiatry. 2016 Oct;3(10):947-953. doi: 10.1016/S2215-0366(16)30188-2. Epub 2016 Aug 23.

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Footnote 23

Schoeler T, Monk A, Sami MB, Klamerus E, Foglia E, Brown R, Camuri G, Altamura AC, Murray R, Bhattacharyya S (2016). Continued versus discontinued cannabis use in patients with psychosis: a systematic review and meta-analysis. Lancet Psychiatry. 2016 Mar;3(3):215-25. doi: 10.1016/S2215-0366(15)00363-6. Epub 2016 Jan 15.

Return to footnote 23 referrer

Footnote 24

Gunn JK, Rosales CB, Center KE, Nuñez A, Gibson SJ, Christ C, Ehiri JE (2016). Prenatal exposure to cannabis and maternal and child health outcomes: a systematic review and meta-analysis. BMJ Open. 2016 Apr 5;6(4):e009986. doi: 10.1136/bmjopen-2015-009986.

Return to footnote 24 referrer

Footnote 25

Grant KS, Petroff R, Isoherranen N, Stella N, Burbacher TM (2018). Cannabis use during pregnancy: Pharmacokinetics and effects on child development. Pharmacol Ther. 2018 Feb;182:133-151. doi: 10.1016/j.pharmthera.2017.08.014. Epub 2017 Aug 25.

Return to footnote 25 referrer

Footnote 26

Noble MJ, Hedberg K, Hendrickson RG (2019). Acute cannabis toxicity. Clin Toxicol (Phila). 2019 Jan 24:1-8. doi: 10.1080/15563650.2018.1548708. [Epub ahead of print]

Return to footnote 26 referrer

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