Is Cannabis Safe to Use?

Facts for young adults aged 18–25 years.

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Organization: Health Canada

Date published: 2018-08-06

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Key messages for young adults

  • In light of cannabis use being legalized in Canada if you are 18 years old and over (or 19 years old in some provinces and territories), it is important to know how using cannabis can affect your health before purchasing it, especially if you’re in your late teens and early twenties.
  • The best way to protect your health is to not use cannabisFootnote1.
  • You are more likely to experience harm from cannabis because your brain is still developing until around the age of 25Footnote2.
  • Shortly after using cannabis, you may have problems paying attention, remembering or learning things, and making decisionsFootnote1 Footnote3. Some of these effects may persist for some time after you stop completely or never fully go away depending on how young you were when you started, how often and for how long you have been using itFootnote1 Footnote3Footnote4.
  • After alcohol, cannabis is the drug most often linked to car accidents Footnote5. Cannabis can affect concentration, attention, coordination and slow reaction timeFootnote3 Footnote6. Using it and driving increases the risk of having a car accident which can result in serious injuries or deathFootnote7.
  • How long the impairing effects of cannabis last depends on how (smoked, inhaled, ingested) and how much was taken, but the effects can last for at least six (6) hours or longer after useFootnote1 Footnote8 Footnote9.
  • Using cannabis and drinking alcohol with or without the use of other drugs such as pain medications (opioids) and tranquilizers (benzodiazepines) further lowers your ability to concentrate and react quickly to emergenciesFootnote5 Footnote10 Footnote11 Footnote12 Footnote13.
  • Using cannabis regularly (daily or almost daily) and over a long time (several months or years), can harm your physical and mental health including becoming physically dependent or addicted to cannabisFootnote1 Footnote3.
  • Higher-strength cannabis products (such as concentrates like “shatter”, wax, dabs) can worsen the mental health effects of cannabis use (such as paranoia and psychosis)Footnote14 Footnote15 Footnote16 Footnote17 Footnote18 Footnote19.
  • Should you experience severe symptoms from cannabis use, such as disorientation, shaking, shortness of breath and/or vomiting, seek immediate medical assistance.
  • If you need more information or support, talk to your doctor or primary care practitioner.

Supporting information

For: Medical and public health professionals, parents, educators and other adult influencers

How can cannabis use affect one’s health?

We still have lots to learn about the physical, mental and emotional effects of cannabis use. However, we do know that there are both short term and long term health hazards.

Every time cannabis is used it can:

  • Impair one’s ability to drive safely or operate equipment. Cannabis can slow reaction times, lower one’s ability to pay attention, and harm coordination Footnote6. Using cannabis and driving can result in a car accident, serious injuries or death Footnote1 Footnote7.
  • Make it harder to learn and remember things. After using cannabis, a person may have problems paying attention, remembering or learning things, and making decisions Footnote3. Using cannabis can reduce one’s ability to perform well on the job or at school Footnote1 Footnote4 Footnote20 Footnote21 Footnote22 Footnote23 Footnote24 Footnote25 Footnote26.
  • Affect mood and feelings. Cannabis can make a person feel very anxious, panicked, sad, and fearful Footnote3.
  • Affects mental health. Cannabis can trigger a psychotic episode (not knowing what is real, experiencing paranoia, having disorganized thoughts, and in some cases having hallucinations) Footnote3.

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

  • Hurt the lungs and make it harder to breathe. Cannabis smoke contains many of the same harmful substances as tobacco smoke Footnote27. Also, like smoking cigarettes, smoking cannabis can damage the lungs and result in a cough or wheezing and other breathing symptoms Footnote28. Preliminary studies on dried cannabis vapourizers suggest that fewer respiratory symptoms might result from vaping, rather than smoking, cannabis Footnote29. More research is needed to better understand the composition and potential health risks of different types of vapourized products (e.g., products that utilize dried cannabis, cannabis concentrates, vape pens) Footnote29.
  • Affect mental health. Using cannabis regularly and continuously over time makes you more likely to experience anxiety, depression, psychosis, and schizophrenia Footnote1 Footnote19 Footnote30 Footnote31. Studies show that stopping or reducing cannabis use can improve these symptoms Footnote32 Footnote33.
  • Become physically dependent or addicted. It is estimated that 1 out of 11 of those who use cannabis in their lifetime will become addicted to cannabis Footnote3. This rate increases to 16% for those who start using cannabis during adolescence and up to 1 out of 2 people who smoke cannabis daily Footnote3 Footnote34. Cannabis addiction may have a major negative impacton one’s everyday life and affect school, relationships with family and friends, sports, extracurricular activities and volunteer work Footnote3.

What about the use of cannabis for medical purposes?

While cannabis can be used by some people for their health problems, determining whether cannabis is appropriate to treat an individual’s symptoms is best made through a discussion with a health care practitioner.

Health Canada has published information to help Canadians and their physicians make informed decisions about the benefits and risks of using cannabis for medical purposes. Visit for more information.

Reporting an adverse reaction to cannabis

Suspected adverse reactions to cannabis should be reported to Health Canada’s Canada Vigilance Program. The program can be contacted toll-free at 1-866-234-2345.

Briefs available in this series

Is cannabis safe to use? Facts for youth aged 13–17 years. 
Does cannabis use increase the risk of developing psychosis or schizophrenia? 
Is cannabis safe during preconception, pregnancy and breastfeeding? 
Is cannabis addictive?


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