Cannabis and cancer (May 2019)

Recent evidence on cannabis use and cancer risk and the benefits of use during cancer treatment

In October 2018, cannabis was legalized for recreational (non-medical) use in Canada under the Cannabis Act. Prior to this, the federal government authorized use of cannabis for medical purposes from licensed producers when prescribed by a health care practitioner via the Marihuana for Medical Purposes Regulations (2013), and the Access to Cannabis for Medical Purposes Regulations (2016).

The Partnership undertook two rapid reviews to assess recent evidence on cannabis and cancer risk as well as the benefits of cannabis use during cancer treatment:

Cannabis does not cure cancer1. The link between cannabis use and cancer risk remains inconclusive and there is insufficient evidence to characterize the potential therapeutic benefits of cannabis as a supportive medication during cancer treatment. High quality evidence is needed to understand potential risks and benefits of cannabis use in relation to cancer.

Expert commentary on the benefits and harms of cannabis use

David Hammond, Applied Public Health Chair for the Canadian Institute for Health Research/Public Health Agency of Canada and professor at the School of Public Health & Health Systems, University of Waterloo

“While some individuals with cancer have reported that cannabis helps in managing treatment symptoms including nausea, appetite loss and pain, there is no evidence that it can ‘cure’ or ‘treat’ cancer. There is growing evidence suggesting that chronic cannabis use may increase the risk of some cancers, particularly when it’s inhaled. Frequent cannabis users should look for other ways to consume the product, avoiding cannabis smoke.”

Peter Selby, Addiction Medicine Clinician Scientist and Chief of Medicine in Psychiatry Division at the Centre for Addiction and Mental Health (CAMH)

“We need better studies to reach firm conclusions about the benefits and harms of cannabis. Risks for cancer are likely due to how people consume cannabis. Inhaling smoke from a burning a plant product, whether it’s tobacco or cannabis, produces known carcinogens. As such, avoiding inhaled cannabis is probably best to reduce one’s risk.

I tailor my advice to people using cannabis recreationally to factors such as their age or intentions behind use. For example, people at risk for addiction or psychosis, or those working in safety-sensitive jobs, should not use cannabis. On the other hand, occasional users should only use legal products of known quality with less potency, avoid using alone or in places where it might be dangerous to do so, and avoid use with alcohol or other drugs.

If there is any indication that cannabis use is causing problems financially, socially, occupationally or medically, I recommend people stop using it or seek addiction services.”

Dr. Craig Earle, medical oncologist at Sunnybrook Hospital and the VP, Cancer Control at the Canadian Partnership Against Cancer

“The evidence is still unclear on whether medical cannabis is a safe and effective therapy for people with cancer and other diseases, but it is currently available in our jurisdiction. Some patients are interested in trying it, and so for those where it seems appropriate I have authorized it at their request. I haven’t yet gotten to the point of actively promoting it, but I have anecdotally seen some patients appear to derive benefit for symptoms like nausea and pain. I look forward to seeing high level evidence about when medical cannabis does and does not work, like we usually require for other medications we prescribe.”

To learn more about ways to reduce health risks when using cannabis, please access Canada’s Lower-Risk Cannabis Use Guidelines.

To learn more about provincial and territorial policies regulating the use and sale of cannabis across Canada, please access the Canadian Centre on Substance Use and Addiction’s interactive map.

Downloadable content

1- NASEM. The National Academies of Sciences, Engineering and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. 2017.