Cannabis health effects
Cannabis and your health
Cannabis contains substances that affect the brain and body, including delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC causes the intoxicating effects of cannabis. CBD is not intoxicating but can still have effects on the brain.
Find resources on substance use and addiction.
On this page
- The short-term effects of cannabis use
- The long-term risks of cannabis use
- The effects of cannabis on young people's health
- Lowering your risks when consuming cannabis
- The effects of cannabis on pregnancy and breastfeeding
- Cannabis for medical purposes
- Cannabis addiction
- Cannabis poisoning
The short-term effects of cannabis use
Everyone's response to cannabis differs 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 coordinationFootnote 1 Using cannabis and then driving or operating equipment can result in an 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 impact your ability to perform well on the job or at school.Footnote 2
- Affect your mental health
- Though cannabis can cause euphoria (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, hallucinating).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 use of THC over a long time increases the risk of cannabis dependence, also called:
- cannabis use disorder
- problematic cannabis use
- 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 (20% THC [200 mg/g] or more) such as resin, hash oil, wax and distillates further increases the risk of mental health problems over time.Footnote 7Footnote 8Footnote 9
- Stopping or reducing your cannabis use can improve your mental health.Footnote 5Footnote 10Footnote 22Footnote 23
- Frequent use of THC over a long time increases the risk of cannabis dependence, also called:
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 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 use of cannabis over a long time can also harm important aspects of your thinking, like learning and memory. Stopping 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 avoid using cannabis or cannabis products completely.
Cannabis can be consumed in different ways. Two common ways are:
- inhalation (smoking or vaping)
- ingestion (eating or drinking)
Each way carries different health and safety risks.
Everyone's response to cannabis is different, depending on:
- THC and CBD content
- any pre-existing medical conditions
- experience with cannabis, frequency of use
- consumption of food, alcohol, other drugs or health products
Everyone's response to cannabis can also differ from one time to the next.
Research suggests that there are ways to reduce the risks:
- 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 with equal or higher amounts of CBD than THC.
- The higher the THC content of a product, the more likely you are to experience adverse effects and greater levels of impairment. CBD is known to 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.
- Frequent use of cannabis over a long time can contribute to mental health problems. These include dependence, anxiety and depression.
- Avoid mixing cannabis and other substances, like alcohol or drugs.
- Using cannabis at the same time as drinking alcohol and/or using other drugs can cause more severe levels of impairment and adverse effects. Other drugs include pain medications (opioids) and tranquillizers (benzodiazepines).
- Avoid using cannabis and driving or operating machinery.
- After alcohol, cannabis is the drug 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. 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 at risk for mental health problems, especially
- problematic substance use
For more information, please see the lower-risk cannabis use guidelines developed by Canadian experts in mental health and addiction.
The effects of cannabis on pregnancy and breastfeeding
Avoid cannabis completely if you are pregnant or breastfeeding. Substances in cannabis are transferred from the mother to child and can harm your unborn or newborn baby.
There may also be other health risks associated with cannabis use during pregnancy and breastfeeding.Footnote 24Footnote 25
If you have questions, visit your health care provider.
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 health care provider make informed decisions about the potential benefits and risks, we have published information on using cannabis for medical purposes.
Cannabis addiction is real, although the risk of addiction is lower than it is for other substances such as:
Using cannabis frequently can lead to a pattern of problematic use or use disorder. This can result in dependence or addiction.
Experiencing a cannabis addiction can cause serious harm to your:
- social life
- school work
- work and financial future
What we know:
- Adolescents who use cannabis frequently can increase their chance of becoming addicted. 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.
Accidentally consuming or consuming too much cannabis at a time can lead to temporary adverse effects, 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
- 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/poisoning, especially if you are a first-time or inexperienced user.
It is also easier to be poisoned when ingesting (eating or drinking) cannabis compared to inhaling cannabis (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.
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, 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 to drivers about:
- 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.
- 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.
- 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.
- 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.
- 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).
- Footnote 6
Gorelick, S. A., & Hermann, R. (2017). Cannabis use and disorder: Epidemiology, comorbidity, health consequences, and medico-legal status. UpToDate. September, 2-150.
- 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
- Footnote 8
Meier MH. Associations between butane hash oil use and cannabis-related problems. Drug and Alcohol Dependence. 2017;179:25-31.
- 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.
- 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.
- Footnote 11
Chadwick B, Miller ML, Hurd YL. Cannabis use during adolescent development: Susceptibility to psychiatric illness. Front Psychiatry 2013 Oct 14;4:129.
- Footnote 12
Rathee, S., & Shyam, R. (2018). Effect of Abstinence on Memory Functions in Cannabis Users. Journal of Psychosocial Research, 13(2), 443-451.
- 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).
- 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.
- 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.
- 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.
- 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.
- Footnote 18
Hudak, M., Severn, D., & Nordstrom, K. (2015). Edible cannabis-induced psychosis: intoxication and beyond. American Journal of Psychiatry, 172(9), 911-912.
- 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
- 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.
- Footnote 21
Chen, P., & Rogers, M. A. (2019). Opportunities and Challenges in Developing Orally-Administered Cannabis Edibles. Current Opinion in Food Science.
- 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.
- 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.
- 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.
- 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.
- 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]
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