What Do We Know About Cannabis?

Philippe Lucas

Reprinted from "Cannabis" issue of Visions Journal, 2009, 5 (4), p.4

“Marihuana is not an approved therapeutic product and the provision of this information should not be interpreted as an endorsement of the use of this product, or marihuana generally, by Health Canada. Since this marihuana product has not been authorized through the Health Canada drug approval process, its safety and efficacy have not been established. The use of this product involves risks to health, some of which may not be known or fully understood.” 1

What do we know about marijuana (cannabis), its therapeutic (healing) potential and its side effects?

According to the Health Canada quote above, it may seem like we don’t know much at all. And yet, a search for “marijuana” or “cannabis” on Google Scholar turns up a total of 563,000 hits. The same search on PubMed (a database of scientific publications) turns up 25,976 published scientific articles on marijuana and/or cannabis.

Cannabis is one of the most studied herbs in the history of mankind. However, as a result of the international prohibition on cannabis, government-funded research has largely examined harms and side effects rather than its potential as a medicine.

Recent developments and discoveries, though, have changed this landscape considerably. In 2005, Health Canada approved Sativex®, a cannabis-based oral spray developed by UK company GW Pharmaceuticals, for treatment of pain in multiple sclerosis.2 And as you read this, most major pharmaceutical companies in the world are studying cannabis and cannabinoids. They all hope to come up with the next treatment for chronic pain, depression, addiction, movement disorders, appetite loss, schizophrenia, diabetes, obesity and Alzheimer’s disease. Many scientists are even looking at this plant and its compounds as a potential cure for cancer.

What does the scientific community know about cannabis?

We know that:

  • Cannabis isn’t nearly as physically dangerous or addictive as either alcohol or tobacco.3

  • It doesn’t lead to violent or criminal behaviour, or decrease motivation.3

  • It’s highly unlikely that smoking cannabis leads to upper respiratory or lung cancer. Evidence suggests that it could actually have a protective effect on the lungs.4

  • It appears to be associated with the potential development of psychosis and schizophrenia in people with a predisposition for these conditions, but this is still a highly debated issue with new evidence emerging every day.5 Additionally, I believe there is evidence to suggest that this may have as much to do with high levels of ammonia resulting from nitrogen-based fertilizers used to grow the cannabis as it does from the plant itself.6-7

  • About 10% of regular users develop a mild psychological or physical dependence on cannabis, but it doesn’t lead to the use of other illicit substances.3 In fact, cannabis is often used as a treatment (or “exit drug”) for addiction to both legal and illegal substances like cocaine,8 crack,9 alcohol10 and opiates.11 (This area of research is the basis for my master’s thesis in the University of Victoria’s Studies in Policy and Practice program.)

What about the social consequences of cannabis use?

In terms of its impact on the Canadian criminal justice system and limited police resources, we know that cannabis prohibition results in more drug arrests than all other illegal substances combined, costing taxpayers over $384 million per year.3 There are more than 50,000 cannabis-related arrests made each year in Canada,3 and over one million Canadians now have criminal records for cannabis-related offences.12 We also know that over 70% of these arrests are for personal possession, rather than for trafficking or cultivation.3

And, despite the legalization of medical cannabis in Canada, most medical users are not protected from arrest and prosecution by our federal program. According to government-funded research, there are currently about one million Canadians using cannabis for medical purposes,13 but fewer than 3,000 patients are currently protected through Health Canada’s Marihuana Medical Access Division (MMAD).14 MMAD has been found unconstitutional five times in as many years when courts in Ontario, Alberta and BC ruled that it created unnecessary obstacles to legally accessing medical marijuana.15 As a result, dozens of critically and chronically ill Canadians—people living with HIV/AIDS, hepatitis C, cancer, MS and other serious conditions—are arrested and forced to defend their medical use in court every year.

Where do we go from here?

As the articles in this issue of Vision will show, there may still be much to learn about cannabis. But through the hard work of world-class researchers, front-line service providers, patients and recreational users like those in the following pages, we are slowly understanding more and more about both its potential harms and benefits.

Substance use, however, is a very complex and emotional issue. It has been influenced by years of often misguided or misinformed anti-drug campaigns. Even amongst the many contributors to this issue, there is some disagreement about how best to regulate access to this plant. Although this social debate will likely continue for some time, it’s clear that criminalizing otherwise law-abiding and responsible adults isn’t supported by the available evidence, nor is it reducing rates of use or potential harms to vulnerable populations.16 In fact, cannabis prohibition may actually be making use more dangerous by driving its production, distribution and use underground and surrendering control and profits to the black market. Additionally, we are missing opportunities to make cannabis use safer through quality control measures, age-restricted access, and evidence-based drug education focused on public health, harm reduction and human rights.

And that leads me to one final thing that we know about cannabis: it has been used at least once by over 44% of Canadians.13 In fact, Canada’s cannabis policies have a very unique distinction: they are the only federal laws that don’t enjoy the majority support of citizens. Recent polls show that over 50% of Canadians support the legalization of cannabis,17 and that over 90% support medical access.18
Ultimately, Canadians want and deserve drug policies based on science and compassion, and not fear and misinformation; that much we know for certain about cannabis.

About the author
Philippe is the founder and Executive Director of the Vancouver Island Compassion Society, a non-profit medical cannabis research and distribution centre (www.thevics.com). He’s also a Graduate Research Fellow with the Centre for Addictions Research of BC, a Victoria city councillor and a federally authorized medical cannabis patient




  1. Health Canada. (2006). Information for the patient: Marihuana (cannabis). www.hc-sc.gc.ca/dhp-mps/marihuana/how-comment/applicant-demandeur/info_patient-eng.php.

  2. Health Canada. (2005). Approval of SATIVEX® with conditions. www.hc-sc.gc.ca/dhp-mps/prodpharma/notices-avis/conditions/sativex_dhcpl_lapds_091289-eng.php.

  3. Nolin, P.C., Kenny, C., Banks, T. et al. (2002). Report of the Senate Special Committee on Illegal Drugs. Ottawa: Senate of Canada. 

  4. Hashibe, M., Morgenstern, H., Cui, Y. et al. (2006). Marijuana use and the risk of lung and upper aerodigestive tract cancers: Results of a population-based case-control study. Cancer Epidemiology Biomarkers and Prevention, 15(10), 1829-1834.

  5. Frisher, M., Crome, I., Martino, O. et al. (2009). Assessing the impact of cannabis use on trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005. Schizophrenia Research. doi:10.1016/j.schres.2009.05.031.

  6. Bélanger-Quintana, A., Martínez-Pardo, M., García, M.J. et al. (2003). Hyperammonaemia as a cause of psychosis in an adolescent. European Journal of Pediatrics, 162(11):773-775.

  7. Moir, D., Rickert, W.S., Levasseur, L. et al. (2008). A comparison of mainstream and sidestream marijuana and tobacco cigarette smoke produced under two machine smoking conditions. Chemical Research in Toxicology, 21(2), 494-502.

  8. Aharonovich, E., Garawi, F., Bisaga, A. et al. (2006). Concurrent cannabis use during treatment for comorbid ADHD and cocaine dependence: Effects on outcome. American Journal of Drug and Alcohol Abuse, 32(4), 629-635.

  9. Labigalini Jr., E., Rodrigues, L.R. & Da Silveira, D.X. (1999). Therapeutic use of cannabis by crack addicts in Brazil. Journal of Psychoactive Drugs, 31(4), 451-455.

  10. Model, K. (1993). The effect of marijuana decriminalization on hospital emergency drug episodes: 1975-1978. Journal of the American Statistical Association, 88(423), 737-747.

  11. Australian Institute of Health and Welfare. (2002). 2001 National Drug Strategy Household Survey: First results. Canberra: AIHW (Drug Statistics Series No. 9). www.aihw.gov.au/publications/phe/ndshs01/ndshs01.pdf.

  12. Erickson, P. & Fisher, B. (1995, October). Canadian cannabis policy: The impact of criminalization, the current reality and future police option. Paper presented at the International Symposium on Cannabis Policy, Criminal Law and Human Rights, Bremen, Germany. www.parl.gc.ca/37/1/parlbus/commbus/senate/Com-e/ille-e/presentation-e/erickson1-e.htm.

  13. Adlaf, E.M., Begin, P. & Sawka, E. (Eds.) (2005). Canadian Addiction Survey: A national survey of Canadians’ use of alcohol and other drugs: Prevalence of use and other harms: Detailed report. Ottawa: Canadian Centre for Substance Abuse. www.ccsa.ca/2005%20CCSA%20Documents/ccsa-004028-2005.pdf.

  14. Health Canada. (2009). Marihuana for Medical Purposes Statistics (July 4, 2008). www.hc-sc.gc.ca/dhp-mps/marihuana/stat/_2008/july-juillet-eng.php.

  15. Lucas, P. (2009). Moral regulation and the presumption of guilt in Health Canada’s medical cannabis policy and practice. International Journal on Drug Policy, 20(4), 296-303.

  16. Reinarman, C. (2009). Cannabis policies and user practices: Market separation, price, potency, and accessibility in Amsterdam and San Francisco. International Journal on Drug Policy, 20(1), 28-37.

  17. Angus Reid Strategies. (2008, May 8). Canadian majority would legalize marijuana. Angus Reid Global Monitor. www.angus-reid.com/polls/view/30688/canadian_majority_would_legalize_marijuana.

  18. Harris, M. (2006, November 2). Most Canadians OK with medicinal marijuana: Poll findings also show almost half back legalization. The Ottawa Citizen. www.medicalmarihuana.ca/poll.html.