Who shouldn’t use medicinal cannabis?

When recommending any therapy, a healthcare provider and patient need consider both the potential benefits and risks. What information is available to guide them when it comes to medical cannabis?

In 2013, the Canadian College of Physicians and Surgeons of Canada asked the federal government to develop explicit indications, precautions and contraindications for medical cannabis so doctors could evaluate which of their patients should, or should not, be given access to medical cannabis.¹

Although it has an information document for practitioners on medical cannabis, Health Canada states upfront: “This document should not be construed as expressing conclusions from Health Canada about the appropriate use of cannabis (marihuana) or cannabinoids for medical purposes.”² Nevertheless, based on contraindications for existing synthetic cannabis medications (nabilone and dronabinol) and the cannabis extract dronabinol, Health Canada suggested the risk/benefit ratio of cannabis needs to be carefully and individually considered for people who:

• Are under the age or 18
• Have a history of hypersensitivity to any cannabinoid or to smoke (if the cannabis is smoked)
• Have severe cardio-pulmonary disease with occasional hypotension (low blood pressure), possible hypertension (high blood pressure), syncope (loss of consciousness) or tachycardia (rapid heart rate)
• Have respiratory diseases such as asthma or chronic obstructive pulmonary disease (COPD)
• Patients with severe liver or renal disease, including chronic hepatitis C
• Have a personal history of psychiatric disorders or a family history of schizophrenia
• Have a history of substance abuse
• Are women of childbearing age not on a reliable contraceptive, planning to become pregnancy, are pregnant, or are breastfeeding.

In additional, it suggests medical cannabis should be used with caution in people who have mood disorders or are taking sedatives or other psychoactive drugs.

In 2014, the College of Family Physicians of Canada (CFPC) produced its first guideline for physicians, focusing on cannabis for the treatment of chronic pain or anxiety.³ In this document, the CPFC not only listed what sort of people might be inappropriate candidates for medical cannabis but also rated the level of the research evidence for their recommendations. Their rating scheme consisted of three levels: Level I evidence is the strongest (well-conducted controlled trials or meta-analyses), followed by Level II (well-conducted observational studies), and the weakest, Level III (consensus of the expert members of the committee writing the guidelines).

To summarize, in this document the CFPC advised doctors to not authorize medical cannabis to patients who:

• Are under the age of 25 (Level II)
• Have a personal history or strong family history of psychosis (Level II)
• Have a current or past cannabis use disorder or another active substance use disorder (Level III)
• Have cardiovascular or respiratory disease (Level III)
• Are pregnant, planning to become pregnant or are breastfeeding (Level II)

In addition, it said caution should be used in recommending cannabis for patients who:

• Have a mood or anxiety disorder (Level II)
• Smoke tobacco (Level II)
• Have risk factors for cardiovascular disease (heart disease and stroke) (Level III)
• Are heavy users of alcohol or take high doses of opioids, benzodiazepines (a class of tranquilizers) or other prescription or over-the-counter sedatives (Level III)

As this summary shows, because of gaps in research on medical cannabis, none of the recommendations were backed by the “gold standard” of evidence, randomized controlled trials (RCTs) or meta-analyses, a type of systematic review that combines and analyzes data from RCTs. Instead, most were based on observational studies or expert opinion. (To find out more about the type of research currently available to guide clinicians and decision-makers, you can check out our evidence summaries and reviews.)

The CFPC guidelines are a start but pain and anxiety are only two of the potential indications for medical cannabis. Moreover, some of the possible contraindications listed in the Health Canada document are not addressed by the CFPC, which can be a point of confusion. More guidelines are needed to address all of the patient populations who may be eligible for medical cannabis, such as those with multiple sclerosis, HIV/AIDs, and cancer. In doing so, ethical and medical issues may arise. For example, should the contraindications in the CFPC report be applied to palliative-care patients? What about people with serious conditions who have tried but not benefited from conventional therapies? A lot of questions remain about the appropriate use of medical cannabis. The work of the Michael G. DeGroote Centre for Medicinal Cannabis Research will provide the sort of information and insights needed for better decision-making and health care.