Rate this article and enter to win
This content was developed with extensive input from the Professional Advisory Board of Student Health 101, which includes two physicians and 12 campus health educators and related specialists.

As the federal government considers legalizing recreational marijuana use, the drug is becoming more accessible in Canada. For anyone who’s choosing to use (or considering using) marijuana, it’s important to unravel what this might mean for them. “Like all drugs, using marijuana can be beneficial or harmful depending on how, when, where, in what dosage, in what form, and by whom it is being used,” says Dr. Gerald Thomas, Collaborating Scientist at the Centre for Addictions Research of British Columbia.

If recreational use becomes legal, responsibly using marijuana involves making decisions based on the best information available. What is that best info? Much of what we hear about marijuana comes via sources pushing their own agenda (pro- or anti-legalization). For various reasons, the effects of mind-altering substances, especially illegal ones, are difficult to determine. “The science of marijuana is still developing,” says Dr. Neil Boyd, Professor and Director of the School of Criminology at Simon Fraser University, British Columbia. “Prohibition has generally limited scientific efforts to expand our knowledge of the drug.”

If you choose to use, here’s how to reduce your risk [printable]

Athletics and driving: Marijuana on the field and in the car

Your athletics

“If marijuana use is more frequent, it can affect fine motor dexterity and visual eye tracking. Imagine how this would affect performance in a high-intensity game like volleyball,” says Dr. Philip Tibbo, Professor of Psychiatry at Dalhousie University, Nova Scotia.

Your driving

“There is consistent evidence that cannabis impairs driving ability and increases risk of a collision,” says Dr. Amy Porath-Waller, Director of Research and Policy at the Canadian Centre on Substance Abuse. “It impairs many different cognitive abilities involved in driving a motor vehicle, including reaction time and the ability to divide attention (between the road, speedometer, traffic, obstacles, etc.). The risk for driving is increased further if you mix even small amounts of alcohol with marijuana.”

What does problematic marijuana use look like?

What effect does marijuana have on the user’s life?

One size will never fit all. Some people are able to use pot often and have a high quality of life, while others suffer academically or emotionally, or become dependent. “Problematic” use is defined loosely by the impact of marijuana use on an individual. Here’s what to look at:

  • Tolerance “Excessive cannabis use can lead to a higher tolerance to the effects of the drug (meaning you’ll need to smoke more to get the desired effect), and even symptoms of withdrawal when use is abruptly stopped,” says Dr. Ryan Vandrey, Associate Professor at the Behavioral Pharmacology Research Unit of Johns Hopkins University School of Medicine, Maryland.
  • Goals and quality of life“Frequent use of cannabis [can] interfere with attaining goals, tending to responsibilities, and interpersonal relationships, and [even with those negative consequences] it gets harder to quit or reduce use,” says Dr. Vandrey.
  • Reason for useUsing marijuana to cope with anxiety, stress, and other issues carries the risk of dependence and learning problems. In addition, self-medicating can prevent users from developing healthy coping skills (such as exercising, journalling, reading, and talking to friends and family). If you use marijuana, try to identify the reasons.
  • Health harms “Cannabis use is associated with a variety of health harms, like problems with cognitive and psychomotor functioning [related to mental processes], respiratory issues, dependence, and mental illness,” says Dr. Jürgen Rehm, Director of the Social and Epidemiological Research Department at the Center for Addiction and Mental Health, Ontario.

Why “problematic use” is not easy to define

  • Marijuana affects people differently The amount of money a user spends on marijuana, and even the amount of marijuana consumed, do not align neatly with the impact on users’ functioning, according to a study by researchers at the University of Southern California (presented at the American Public Health Association conference, 2015).
  • Safety and risk depend on how a drug is used The key is not so much about whether a drug is legal versus illegal, or socially acceptable versus stigmatized. It’s more about how the drug is used: frequency, potency, method of delivery, the age when a person starts using regularly, and so on.
  • It’s hard to know what causes problematic outcomes Some studies link marijuana use to other risky behaviours or poor outcomes. For example, in a study of university and college students, the following experiences were associated with using marijuana within the last 30 days: being taken advantage of sexually, not using condoms in sexual encounters, heavy drinking, poor exam performance, missing class, and getting hurt or injured. But correlation is not causation. Maybe marijuana caused bad test scores; maybe students smoked marijuana in an attempt to cope with bad test scores; or maybe the students who used marijuana also skipped class, resulting in bad test scores. Researchers are working to figure out cause and effect.

Source: Correlates and predictors of marijuana use among US undergraduates. In 143rd APHA Annual Meeting and Exposition (October 31–November 4, 2015).

Signs of problematic marijuana use

Signs of a marijuana use disorder include certain health problems and failure to meet goals and responsibilities at school or work.

  • Craving marijuana and/or being high much of the time
  • Needing increased amounts of marijuana to maintain the desired effects
  • Withdrawal symptoms (e.g., mood or sleep changes)
  • Using marijuana in combination with alcohol and/or other drugs
  • Using marijuana to the point that it negatively affects life and functioning (e.g., driving under the influence or social withdrawal)
  • Using marijuana to cope with anxiety, stress, insomnia, or other issues
  • Using high-potency forms of marijuana, such as hash oil extracts and concentrates (sometimes called “wax” or “shatter”)

Nearly three in ten marijuana users had a marijuana use disorder in 2012–13, according to a 2015 study in the Journal of the American Medical Association.

Help with drug dependence (Canadian Centre on Substance Abuse)

Marijuana use may increase alcohol risk
Marijuana users may be more likely to develop an alcohol use problem, recent research suggests. Marijuana users are five times more likely than non-users to abuse alcohol or become dependent on it, according to a 2016 study in Drug and Alcohol Dependence. In adults with an existing alcohol use disorder, using marijuana was associated with ongoing drinking problems; the adults who did not use marijuana appeared better able to abstain from alcohol, the same study suggests.

For help with problematic substance use, make an appointment with student health or counselling services on your campus.

Your brain on pot later: What’s up with long-term use?

Long-term, frequent marijuana use starting in adolescence or early adulthood may impair the brain chronically and irreversibly—or it may not. That uncertainty speaks to the difficulties inherent in researching the effects of substance use.

If marijuana can cause long-term harms, those effects likely vary according to when the individual started using, how much and how often they used, how recently they used, the potency of the marijuana used, and other factors.

Marijuana may affect IQ

In a 2012 study of New Zealanders, those who started using marijuana heavily in adolescence experienced an average decline of 8 IQ points by age 38 (non-users experienced an average 1 IQ point increase over the same time span). The IQ drop persisted even after the users quit marijuana. The participants who started using marijuana as adults did not experience the same IQ decline, suggesting that marijuana use may have neurotoxic effects during critical developmental stages (Proceedings of the National Academy of Sciences).

Marijuana may affect life outcomes

Chronic marijuana use is associated with life setbacks, research suggests. A 2003 study compared frequent marijuana users with their peers from similar socioeconomic backgrounds who reported much less marijuana use. The frequent users were less likely to have graduated from university and had lower incomes, according to Psychological Medicine (2003). The frequent, chronic users believed that marijuana was to blame for their ongoing struggles.

But we don’t know for sure

These research findings are difficult to interpret. It’s possible that other factors explain the effects. For example, maybe the people who used marijuana heavily also used alcohol or other potentially harmful substances, or routinely skipped class as teens, resulting in lower IQ scores later. Which comes first? Maybe less motivated people use more marijuana, rather than marijuana causing that loss of motivation.

Marijuana on campus: What it means for you

Real concerns remain. Getting caught using marijuana can narrow your opportunities in various ways:

  • Academics Students caught using marijuana may be suspended or expelled, depending on the policies in place at their institutions. Check your student code of conduct for more information.
  • Athletics Drug policies around testing and penalties for university athletes vary from school to school. Under Canadian Interuniversity Sport guidelines, testing positive for marijuana can result in student-athlete sanctions.
  • Employment Although drug testing is rarely conducted at Canadian workplaces, it can be used to reduce industrial accidents related to drug use—primarily in situations where safety is a concern. THC can be detected in your system using a urine test for up to 12 weeks after usage (depending on how much and how often you use). Some companies also drug test their employees.
  • Driving Driving under the influence of alcohol or drugs, including marijuana, is illegal. First offences can result in a fine, loss of driving ability for up to a year, and potential jail time.

How does Canada penalize drivers who use marijuana?

Is moderate marijuana use safer than drinking?

Using marijuana responsibly means managing your consumption so you’re avoiding harm to yourself or others. “The safety of marijuana use partially depends on the amount you intake, and partially on the age you begin regular use,” says Dr. Philip Tibbo, Professor of Psychiatry at Dalhousie University, Nova Scotia.

Marijuana effects are highly variable
The effects depend on its potency, the method of delivery, and how it is used (where, why, how often, etc).

Moderate use is not clearly defined
“For marijuana, I advise (for those who choose to use) smaller doses of lower potency preparations, less frequently. That may mean several hits from a joint once or twice a week,” says Dr. Davis Smith, a practicing internist based in Connecticut, and US Medical Director of Student Health 101. (Yes, this is still vague; it’s difficult to determine potency or define a hit. The absence of clarity is a reason to be cautious.) Avoid mixing marijuana and other substances, including medications, says Dr. Pierre-Paul Tellier, Director of Student Health Services at McGill University, Quebec.

It makes sense to avoid edibles and resins
Dried marijuana (the flowering tops and leaves of plants) is generally less potent than hashish (dried and compressed resin extracts) and hash oil extracts. Edibles take longer to have an effect on the user, and the quantity consumed is trickier to control (compared to smoking), increasing the likelihood of overuse.

It’s difficult to compare marijuana and alcohol for safety
Any comparison depends on the potency of the substances, how they are consumed, and other factors. “Infrequent, small consumption of marijuana is, in most cases, unlikely to be more harmful than low-risk alcohol use (e.g., a couple of beers twice a week),” says Dr. Smith. Marijuana is generally considered less harmful than alcohol, says Dr. Thomas, “because alcohol carries significant risk of lethal overdose and is directly associated with violence, injuries, traffic crashes, and other major harm.” (Until we have a better understanding of marijuana’s effects, this type of comparison is tentative.)

Frequent, heavy THC consumption appears harmful
“Frequent use of marijuana, particularly among those under 25, can have a negative impact on the user’s brain and mental concentration,” says Dr. Amy Porath-Waller, Director of Research and Policy at the Canadian Centre on Substance Abuse. Researchers are working to better understand what that harm looks like.

Your brain on pot now

Your mood

When marijuana feels awe-ful
For many people, marijuana feels good. Some find marijuana helps them relax or feel more enthusiastic about life. They may express themselves more freely or feel more empathic, potentially deepening their social bonds. For some, marijuana heightens sensory experiences (e.g., food tastes better) and creative thinking.

When marijuana feels awful
Not everyone experiences pleasant sensations; some people’s experiences will be more negative and may include feelings of distrust, panic, or fear. “Studies indicate that some of the acute effects of marijuana, such as anxiety and paranoia, depend on different factors,” says Dr. Porath-Waller. “How much are you using? What is the potency? These can influence a student’s unique experience of using marijuana.”

When is euphoria a red flag?
“Marijuana use stimulates the brain’s reward centre, which is a key motivator for why people use psychoactive drugs,” says Dr. Porath-Waller. “If students start using higher potency marijuana to achieve this effect, there is the potential for increased risk of negative effects from the drug.”

Your grades

There is clear evidence that marijuana impairs memory and learning during use and for several days afterward. “Students [who] go to class high cannot be as productive as if they’re sober,” says Dr. Tibbo. “You can’t retain information as well.”

As use increases, so does the risk to attention, concentration, and memory. What does heavy use mean for students? “If a person is a chronic user, the impact of the substance will continue even if a student stops using it a day or two before a high-stake event, such as an exam,” says Dr. Tellier.

Right side of the law

Recreational use of marijuana is still illegal in Canada. Using marijuana continues to bring the risk of encounters with law enforcement and a range of negative consequences.

The use of medicinal marijuana is permitted under the Marihuana for Medical Purposes Regulations (MMPR); Canadians with legally-required documentation can obtain safe access to dried marijuana. For more info on marijuana and Canadian law, see Find out more.

Only 18 percent of Canadian university and college students said they had used marijuana in the last 30 days, in a national, anonymous survey.

“Students may think most of their friends are using marijuana, but the majority of them are not.” —Dr. Pierre-Paul Tellier, Associate Professor of Family Medicine and Director of Student Health Services at McGill University, Quebec, and Medical Director of Student Health 101.

Source: American College Health Association, Spring 2016

Get help or find out more

If you show signs of problematic marijuana use, consider seeking confidential support from campus health and counselling services.

Marijuana legalization in Canada: CBC News

What does legalization mean for Canada: MacLean’s

How to stop smoking pot: The Fix

The Short and Tragic Life of Robert Peace: Jeff Hobbs (Scribner, 2014)

You must enter your name, email, and phone number so we can contact you if you're the winner of this month's drawing.
Your data will never be shared or sold to outside parties. View our Privacy Policy.

What was the most interesting thing you read in this article?

If you could change one thing about , what would it be?


..you will apply to everyday life?

..caused you to get involved, ask for help,
utilize campus resources, or help a friend?

Tell us More
How can we get more people to read ?
First Name:

Last Name:


Phone Number:

What was the most interesting thing you read in this article?

If you could change one thing about , what would it be?


..you will apply to everyday life?

..caused you to get involved, ask for help,
utilize campus resources, or help a friend?

Tell us more.
How can we get more people to read ?
First Name:

Last Name:


Phone Number:


..you will apply to everyday life?

..caused you to get involved, ask for help,
utilize campus resources, or help a friend?

Tell us more.
How can we get more people to read ?

First Name:

Last Name:


Phone Number:

Article sources

Ruben Baler, PhD, health scientist, National Institute on Drug Abuse, Washington, DC.

Nick Boyd, LLM, Professor and Director of the School of Criminology, Simon Fraser University, British Columbia.

Jason R. Kilmer, PhD, Assistant Professor, Psychiatry and Behavioral Sciences; Assistant Director, Health and Wellness for Alcohol and Other Drug Education, University of Washington.

Donald Misch, MD, Associate Vice Chancellor for Health and Wellness, Associate Professor, University of Colorado School of Medicine.

Ethan Nadelmann, JD, PhD, Executive Director, Drug Policy Alliance.

Amy Porath-Waller, PhD, Director of Research and Policy, Canadian Centre on Substance Abuse, Ontario.

Marsha Rosenbaum, PhD, Director Emerita, Drug Policy Alliance (San Francisco office); author, Safety First: A Reality-Based Approach to Teens, Drugs and Drug Education (Drug Policy Alliance, 2014).

Matthew J. Seamon, PharmD., Chair and Associate Professor of Pharmacy Practice, Nova Southeastern University, College of Pharmacy, Florida.

P. Davis Smith, MD, Internist, Director of Health Services, Westminster School, Simsbury, Connecticut; Medical Director, Student Health 101.

Pierre-Paul Tellier, MD, Associate Professor of Family Medicine; Director of Student Health Services, McGill University, Quebec.

Gerald Thomas, PhD, Collaborating Scientist, the Centre for Addictions Research of British Columbia.

Philip Tibbo, PhD, Professor of Psychiatry, Dalhousie University, Nova Scotia.

Ryan Vandrey, PhD, Associate Professor, Behavioral Pharmacology Research Unit, Johns Hopkins University School of Medicine, Maryland.

American Civil Liberties Union. (2013, June). The war on marijuana in black and white. ACLU Foundation.

American College Health Association. (2016). American College Health Association—National College Health Assessment II: Canadian Reference Group Executive Summary Spring 2016. Hanover, MD: American College Health Association, 2013.

Barton, B., Bulmer, S., & Misencik, L. (2015, November). Correlates and predictors of marijuana use among US undergraduates. In 143rd APHA Annual Meeting and Exposition (October 31–November 4, 2015). American Public Health Association. Retrieved from https://apha.confex.com/apha/143am/webprogram/Paper318939.html

Beirness, D. J. & Porath-Waller, A. J. (2015). Clearing the smoke on cannabis: Cannabis use and driving. Canadian Centre on Substance Abuse. Retrieved from https://www.ccsa.ca/Resource%20Library/CCSACannabis-Use-and-Driving-Report-2015-en.pdf

Blaszczak-Boxe, A. (2014, September 30). Hidden risk? Marijuana may be bad for your heart. Live Science. Retrieved from https://www.livescience.com/48073-marijuana-heart-attack-risk.html

Canada Marijuana Doctors. (2013). Canada marijuana laws and legal provinces. Retrieved from https://canada.marijuanadoctors.com/medical-marijuana/index

Canadian Centre on Substance Abuse. (2016). Drug-impaired driving. Retrieved from https://www.ccsa.ca/Eng/topics/Impaired-Driving/Drug-Impaired-Driving/Pages/default.aspx

Canadian Interuniversity Sport. (n.d.). 2015-16 CIS By-laws, policies, and procedures. Retrieved from https://en.cis-sic.ca/information/members_info/bylaws_policies_procedures

CBC News. (2011, Oct 27). Legalize marijuana sales, say B.C. experts. CBC News. Retrieved from https://www.cbc.ca/news/canada/british-columbia/legalizemarijuana-sales-say-b-c-experts-1.1054353

Centre for Addiction and Mental Health. (2014, October 9). CAMH releases new Cannabis Policy Framework [Press release]. Retrieved from https://www.camh.ca/en/hospital/about_camh/newsroom/news_releases_media_advisories_and_backgrounders/current_year/Pages/CAMH-releases-new-Cannabis-Policy-Framework.aspx

Crépault, J. F. (2014). Cannabis policy framework. Centre for Addiction and Mental Health. Retrieved from https://www.camh.ca/en/hospital/about_camh/influencing_public_policy/documentscamhcannabispolicyframework.pdf

Crane, N. A., Schuster, R. M., Fusar-Poli, P., & Gonzalez, R. (2013). Effects of cannabis on neurocognitive functioning: Recent advances, neurodevelopmental influences, and sex differences. Neuropsychology Review, 23(2), 117–137.

Do, T. T. (2014, March 7). Marijuana reform: 5 things to know about possible changes to the law. CBC News. Retrieved from https://www.cbc.ca/news/politicsmarijuana-reform-5-things-to-knowabout-possible-changes-to-the-law-1.2560834

Filbey, F. M., Aslan, S., Calhoun, V. D., Spence, J. S., et al. (2014). Long-term effects of marijuana use on the brain. Proceedings of the National Academy of Sciences, 111(47), 16913–16918.

Foote, A. (2016, Feb 22). Marijuana misinformation putting young people’s health at risk, experts say. CBC News. Retrieved from https://www.cbc.ca/news/canada/ottawa/marijuana-health-risk-myth-youth-1.3458672

Gorski, D. (2014, July 7). Medical marijuana as the new herbalism. Science-Based Medicine. Retrieved from https://www.sciencebasedmedicine.org/medical-marijuana-as-the-new-herbalism-part-1-the-politics-of-weed-versus-science/

Government of Canada. (2016, February 15). Marihuana for Medical Purposes Regulations. Retrieved from https://www.laws-lois.justice.gc.ca/eng/regulations/SOR-2013-119/

Gruber, A. J., Pope, H. G., Hudson, J. I., & Yurgelun-Todd, D. (2003). Attributes of long-term heavy cannabis users: A case-control study. Psychological Medicine, 33(8), 1415–1422.

Hall, J. (2013). Is marijuana dangerous? Should it be legal? A Q & A with addiction researcher Bernard Le Foll. University of Toronto. Retrieved from https://news.utoronto.ca/marijuana-dangerous-should-it-be-legal

Hasin, D. S., Saha, T. D., Kerridge, B. T., Goldstein, R. B., et al. (2015). Prevalence of marijuana use disorders in the United States between 2001–2002 and 2012–2013. JAMA Psychiatry, 72(12), 1235–1242.

Health Canada. (2014). Drugs and health products—Information for law enforcement. Retrieved from www.hc-sc.gc.ca/dhp-mps/marihuana/law-loi/index-eng.php

Johnston, L. D., O’Malley, P. M., Bachman, J. G., Schulenberg, J. E., et al. (2015). Monitoring the Future national survey results on drug use, 1975-2014: Volume II, college students and  adults ages 19–55. Ann Arbor, MI: Institute for Social Research, The University of Michigan, 416 pp.

Mayotte, B. (2015, April 15). Drug convictions can send financial aid up in smoke. US News & World Report. Retrieved from https://www.usnews.com/education/blogs/student-loan-ranger/2015/04/15/drug-convictions-can-send-financial-aid-up-in-smoke

MedicalMarijuana.ca. (2016). Marijuana laws. Retrieved from https://medicalmarijuana.ca/learning-center/marijuana-laws

Meier, M. H., Caspi, A., Ambler, A., Harrington, H., et al. (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences, 109(40), E2657–E2664.

Mittelman, M. A., Lewis, R. A., Maclure, M., Sherwood, J. B., et al. (2001). Triggering myocardial infarction by marijuana. Circulation, 103(23), 2805–2809.

National Institute on Drug Abuse. (2015). Marijuana. Retrieved from https://www.drugabuse.gov/publications/drugfacts/marijuana

Perkins, H. W. (1997). College student misperceptions of alcohol and other drug norms among peers: Exploring causes, consequences, and implications for prevention programs. Designing alcohol and other drug prevention programs in higher education. Bringing Theory Into Practice. 177–206.

Pope, H. G., Gruber, A. J., & Hudson, J. I., Cohane, G., et al. (2003). Early-onset cannabis use and cognitive deficits: What is the nature of the association? Drug & Alcohol Dependence, 69(3), 303–310.

Russell, L. D., & Arthur, T. (2015). “That’s what ‘college experience’ is”: Exploring cultural narratives and descriptive norms college students construct for legitimizing alcohol use. Health Communication, 1–9.

Substance Abuse and Mental Health Services Administration. Results from the 2014 National Survey on Drug Use and Health: Summary of national findings. Rockville, MD: Substance Abuse and Mental Health Services Administration; 2014. HHS Publication No. (SMA) 14-4887. NSDUH Series H-49.

Thomson, A. (2016, January 15). Expert panel seeks to dispel myths about marijuana’s effects on adolescents. 680 News. Retrieved from https://www.680news.com/2016/01/15/expert-panel-seeks-to-dispel-myths-about-marijuanas-effects-on-adolescents/

Urbina, I. (2013, June 3). Blacks are singled out for marijuana arrests, federal data suggests. New York Times. Retrieved from https://www.nytimes.com/2013/06/04/us/marijuana-arrests-four-times-as-likely-for-blacks.html

Volkow, N. D., Baler, R. D., Compton, W. M., & Weiss, S. (2014). Adverse health effects of marijuana use. New England Journal of Medicine, 370, 2219–2227.

Weinberger, A. H., Platt, J., & Goodwin, R. D. (2016). Is cannabis use associated with an increased risk of onset and persistence of alcohol use disorders? A three-year prospective study among adults in the United States. Drug and Alcohol Dependence, DOI:10.1016/j.drugalcdep.2016.01.014

Wong, C. F., Iverson, E., Sperandeo, M., Kaplan, C., et al. (2015). Conceptualizing problematic marijuana use among marijuana-using young adults: One size does not fit all. In 143rd APHA Annual Meeting and Exposition (October 31-November 4, 2015). American Public Health Association. Retrieved from https://apha.confex.com/apha/143am/webprogram/Paper330179.html

Lucy Berrington is a health writer, editor, and communications manager. Her work has been published in numerous publications in the US and UK. She has an MS in health communication from Tufts University School of Medicine, Massachusetts, and a BA from the University of Oxford, UK.

Zachary Siegel is a writer and researcher based in Chicago. He covers drugs, science, and culture, and studies substance use at DePaul University, Illinois.