Thank you, Mr. Chairman and members of the committee.
I am currently medical director of the substance use service at Women's College Hospital in Toronto, and an associate professor in the department of family medicine. I would like to acknowledge my colleagues Sheryl Spithoff, Anita Srivastava, Suzanne Turner, and Sharon Cirone. Their work on cannabis has formed the basis for this talk.
I will begin by thanking the committee for undertaking this study because cannabis use in Canada is an extremely important public health issue. A recent UNICEF study found that Canadian teens aged 11 to 15 are the highest users of cannabis in the western world. An estimated 28% have used cannabis at least once in the past year. The 2011 Canadian alcohol and drug use monitoring survey study on youth aged 15 to 24 reported that 22% of adolescent males and 10% of females are daily or weekly users.
I'll now briefly summarize the major health effects of cannabis.
Cognitive effects—daily smokers experience impairment in attention, psychomotor function, and recall. Chronic cannabis use is associated with persistent neuropsychological deficits, even after a period of abstinence. Since the long-term studies are observational, causality cannot be established.
Cannabis use disorder—a review by Professor Kalant estimated that 7% to 10% of regular smokers meet criteria for cannabis dependence. Cannabis use disorder can have a devastating impact on an individual's work and school performance, social relationships, mood, and quality of life.
Psychosis is another major problem with cannabis. Observational studies have demonstrated an association between cannabis use in adolescence and persistent psychosis. Large cohort studies have demonstrated that cannabis use often precedes the development of psychosis, suggesting that it is an independent risk factor. The risk increases with the dose of cannabis smoked.
Anxiety—although a causal relationship has not been confirmed, there is a strong relationship between cannabis use and anxiety and mood disorders as well as suicidal ideation. Acute cannabis use can trigger anxiety and panic attacks.
Cancer—while previous studies have had conflicting results, a recent long-term 40-year cohort study of 50,000 males found that regular cannabis smoking was associated with a twofold risk of lung cancer, after controlling for cigarette smoking and other risk factors.
Cardiovascular disease—cannabis smoking causes acute physiological effects including elevations in blood pressure and heart rate and blood vessel constriction. There have been case reports of young people suffering heart attacks and strokes shortly after smoking cannabis.
Respiratory disease—although it is difficult to control for the confounding effects of tobacco smoke, evidence suggests that heavy cannabis smoking may be an independent risk factor for chronic obstructive lung disease.
I will now discuss groups at high risk for cannabis-related problems.
Youth who smoke cannabis appear to be at greater risk than older adults for cannabis-related harms. Cohort studies have found that cannabis use in adolescence is associated with criminal activity, suicidal ideation, use of other drugs, and poor school and work performance. Cannabis use disorder may be considerably more common among young smokers than older adults. In a prospective study, 30% of youth aged 14 to 24 reported at least one symptom of cannabis use disorder. Adolescent smokers also appear to be at increased risk for persistent and long-term cognitive impairment, possibly because cannabis may induce persistent structural changes in the developing brain.
As for cannabis and driving, cannabis use prior to driving is a risk factor for motor vehicle accidents. Experimental studies have shown that cannabis impairs critical driving skills such as reaction time. Combining alcohol with cannabis increases the risk of motor vehicle accidents to a greater extent than if either drug is used alone.
Finally, regarding pregnancy, preliminary evidence links cannabis use during pregnancy to subtle neurodevelopmental abnormalities in infants, and cannabis can be classified as a teratogen. Cannabis enters the breast milk, and breastfeeding is contraindicated in cannabis smokers.
So why do so many Canadians smoke marijuana, given the harms?
Canadians appear to view cannabis as a harmless herb, and this may be why our per capita use is so high. In a survey of adults in three countries, Canadians were more likely to view cannabis as harmless, and were more likely to have tried cannabis, than were adults in Sweden or Finland.
Public perception of risk correlates with the level of use. An American survey found that the percentage of senior high school students who believe that regular marijuana smoking is harmful dropped from over 70%, in 1993, to 40%, in 2013, while the percentage of high school seniors who smoked daily rose from 2.4% to 6.5% during that time period.
What should be done?
I believe that the first step is to prevent the unintended harms caused by the new medical marijuana regulations that allow physicians to prescribe dried cannabis. This will enhance the public's perception that marijuana is not only harmless but therapeutic. After all, if Health Canada allows marijuana to be prescribed by physicians, it must be a safe and effective medicine.
The evidence suggests otherwise. Smoked cannabis has negligible therapeutic benefits. Pharmaceutical cannabinoids are far safer and at least as effective, and prescribing marijuana will increase diversion and cannabis-related harms.
I will discuss each of these points in turn.
The evidence in support of smoked cannabis is very weak. To date, five control trials have examined smoked cannabis in the treatment of chronic pain. The trials found that it was superior to a placebo for neuropathic pain, but the trials were small and only lasted between one to 15 days. Most people who smoke cannabis for medical reasons do not have severe neuropathic pain, but have conditions commonly seen in primary care, such as fibromyalgia or low back pain. Numerous safe and effective treatments are available for these conditions. Furthermore, pharmaceutical cannabinoids are far safer and have greater evidence of benefit than smoked cannabis.
Two cannabinoids are available in Canada: nabilone or Cesamet; and Sativex, an oral spray that contains a mixture of THC and cannabidiol. These and other oral cannabinoids have far greater evidence of efficacy. The studies have been much longer, and comparisons have included not just placebos but other analgesics. There is preliminary evidence that oral cannabinoids cause better pain relief than smoked cannabis. Furthermore, oral cannabinoids have fewer euphoric and cognitive effects than smoked cannabis, cause less impairment in driving skills, and are associated with low rates of misuse.
Widespread cannabis prescribing by physicians will increase the social and psychiatric harms of cannabis.
Relative to other pain patients in primary care, a higher proportion of medical marijuana users are younger males with mental health problems or substance use disorders. Prescribing cannabis to these high-risk patients may adversely affect their work and school performance, worsen their anxiety and substance use disorders, and increase their risk of motor vehicle accidents.
Furthermore, it may contribute to the illicit drug trade. In a study of adolescents attending an addiction treatment program in the U.S., 47% reported using marijuana supplied to them by a registered medical marijuana patient.
How do we reduce the impact of the new regulations? The most urgent step is for a credible national medical organization, such as the College of Family Physicians of Canada, to develop evidence-based guidelines for prescribing smoked cannabis. Guidelines will give physicians solid grounds on which to make prescribing decisions. Physicians are facing a deluge of requests to prescribe cannabis, and guidelines will give them the support they need to refuse to prescribe cannabis when medically unnecessary or unsafe.
A related step is to limit the dose and THC concentration of medical cannabis. Distributors are selling cannabis strains with THC concentrations of up to 30% or higher, and Health Canada allows physicians to prescribe up to five grams a day. This dose and this concentration are both dangerous and excessive. The amount needed to control chronic pain is probably no more than 400 milligrams of 9% THC cannabis, or one puff four times a day.
I also believe that the provincial medical colleges should regulate the medical cannabinoid clinics that are being established in Toronto, Vancouver, and probably other cities. Although it is too early to say, I am concerned that the physicians in these clinics will prescribe cannabis to large numbers of patients, as has happened in the U.S. The colleges should ensure that cannabinoid clinics conduct comprehensive patient assessments, have explicit and evidence-based prescribing policies, and do not have any financial conflicts of interest, such as charging patient fees or investment in cannabis companies.
Beyond medical marijuana, public health organizations need to conduct public health campaigns to counter the prevailing myth that cannabis is harmless and therapeutic. Physicians, nurse practitioners, and other primary care providers have an essential role in any public health initiative. Evidence indicates that adolescents are open to advice from their physician on substance use. Primary care providers should regularly ask all patients about cannabis use and should educate them on the risks.
Patients with cannabis-related problems should be offered advice and counselling and referral to addiction services if they are unable to quit or reduce their use. There is strong evidence that primary health care providers' interventions for alcohol, tobacco, and opioid problems are effective. It seems likely that the same will hold true for cannabis problems, although research on this is in its early stages.
Primary health care is the only realistic way to reach the large numbers of patients who smoke cannabis and the large numbers who are at risk for cannabis-related harms.
Thank you.