Health Central asks pain specialist Dr Mark Ware, Chief Medical Officer of Canopy Growth, the largest cannabis grower in the world about his views on the benefits and risks and future of medicinal cannabis.

What do you perceive as the main health benefits of medicinal cannabis for New Zealanders?

Dr Ware: Cannabinoids represent a novel class of medicines for a wide range of symptoms including pain, spasticity, nausea, anxiety and seizures. It is rare for any one class of drug to have such a broad spectrum of effect – and we believe that these effects are supported by tremendous scientific advances in our understanding of the body’s own endogenous system.

The endogenous system (also known as the endocannabinoid system – ECS) consists of cannabinoid molecules and receptors, known to play an important role in a wide range of health conditions and processes, including inflammation, sleep, pain, memory, digestion, immune function, neuroprotection, and more.

The phytocannabinoids (such as THC and CBD) that are produced by the cannabis plant also interact with the receptors of your ECS. This could partly explain why cannabis seems to have an effect on such a wide range of symptoms and conditions.

What is your response to concerns raised about memory loss, panic and paranoia from using cannabis to treat a medical condition?

Dr Ware: The effects of THC on the cannabinoid receptors in the brain may have both positive and negative effects. Negative effects depend very much on the dose (especially related to THC), mode of administration (inhalation or oral), age of patient, experience with cannabis and frequency of use.

Under medical supervision, and at therapeutic doses, cannabinoids are very well tolerated and may have only mild to moderate effects such as dizziness and drowsiness. At large doses, particularly in young people and used often for recreational purposes, there may often be effects on cognition, brain development and psychosis in people at risk of schizophrenia. In medical use, side effects can be minimised by using low doses and with careful screening of patients with an active history of mental health disorders.

Does a law change in this area risk doctors becoming enablers for the recreational use of cannabis?

Dr Ware: Patients have not needed recreational use legislation to legitimise cannabis. In Canada, and globally, medical cannabis policy has been driven by patients. In fact, in Canada, we are already seeing a strong push from patients that are worried the introduction of adult recreational use will delegitimise medicinal cannabis. Companies that choose to operate in both medical and recreational markets need to ensure that patients requiring pharmaceutical grade product are not left in the dark on the recreational demand.

In markets that aren’t as mature as Canada, that have an established cannabis industry, I would rather ask doctors, “what is at risk if doctors do NOT become the gatekeepers of medical cannabis?”.

Restricted access to medical cannabis has implications on clinical care. Patients with a range of conditions are already self-medicating with cannabis, usually from illicit and unregulated sources. Therefore, there may be important safety and quality control issues for consumers, such as them hiding their uses from the treating physician, preventing adequately informed shared clinical decision making. Illicit use also does not allow for important research to be conducted on safety and effectiveness which could be better informed by access to regulated therapeutic cannabis products.

The fact that this has been a patient push from the beginning means that patients do not want to be left in the dark on this topic, they also don’t want to feel judged. Patients want access to regulated and safe product and, most importantly, they want to be able to speak to their doctor about this.

How can medicinal cannabis help New Zealanders struggling with addiction?

Dr Ware: While research still needs to be done, the use of medical cannabis in battling addiction to harmful drugs has been promising thus far, and globally we are seeing more research on this.

In Australia, the University of Sydney’s Lambert Initiative for Cannabinoid Therapeutics is undertaking research on the use of cannabinoid therapeutics to treat methamphetamine “ice” addiction.

In Canada, early research has shown that medical cannabis could have a stabilising impact for people with opioid-use disorder, improving their quality of life and offering a pathway to long-term treatment solutions. In a study published by the British Columbia Centre on Substance Use (BCCSU), researchers found that individuals initiating opioid agonist treatment who reported using cannabis on a daily basis, were approximately 21% more likely to be retained in treatment at six months than non-cannabis users.

Previous research from the BCCSU has also found that using cannabis every day was linked to a lower risk of starting to inject drugs and that intentional cannabis use preceded declines in crack use among crack cocaine users.

The potential of cannabis used as a therapy in addressing the opioid overdose crisis and other substance use disorders is promising, and globally we are seeing areas that are most heavily impacted by the epidemic investing in evidence-based solutions last year. For example, the government of British Columbia allocated half a million dollars to fund research and clinical trials on how cannabis products can be used to address the overdose crisis that currently haunts the streets of Vancouver and the wider British Columbia area.

What can New Zealand learn from Canada’s experience with introducing medicinal cannabis?

Dr Ware: Earlier I spoke about the importance of doctors being able to speak to their patients about medical cannabis, but as a physician myself, I understand the pressures doctors face, particularly with requirements from regulators/colleges to complete continuing education programs.

In Canada, medicinal cannabis has been legal for 20 years, however, evidence suggests that doctors remain woefully uninformed about cannabis. The Canadian Medical Association has consistently refused to develop or facilitate medical education on cannabis use for physicians for 20 years, including programs developed and accredited by independent non-profit organisations. The College of Family Physicians of Canada, from 2015 to 2018, refused to accredit any educational programs on cannabis (I gave presentations at Continuing Medical Education [CME] programs on cannabis where my talk was the only one that was not allowed for CME credit).

Education and health go hand in hand, and while Canada has led the world in cannabis reform there are definitely things that can be learnt from our mistakes and everything comes back to good, balanced education.

What’s the difference between CBD & THC and what therapeutic benefits do they offer, if any?

Dr Ware: People living with chronic pain, mood disorders like anxiety and depression, and sleep problems may well be asking about cannabis since both CBD and THC – the two primary cannabinoids in cannabis – show promise as therapeutic tools for these and other symptoms. While cannabis research and education is expanding, a variety of quality-controlled and regulated products will be important to meet the needs of patients.


  • Pre-clinical and some clinical evidence suggests that CBD may be helpful for reducing inflammation, seizures, and anxiety. It is also known to be an antipsychotic and may be prescribed as an anti-seizure medication, in high doses, for treatment-resistant childhood epilepsy.
  • CBD does not cause the intoxicating, euphoric effects that can be caused by THC. In fact, CBD appears to be able to mitigate some of the potential side effects of THC, such as nervousness, when they are taken together.


  • THC is the most researched cannabinoid for therapeutic benefits, with research indicating THC can be helpful for chronic pain, nausea, muscle spasticity in MS, and appetite improvement.
  • Patients do not need to experience euphoria to get benefits from medical cannabis. This means that even if they are consuming low doses of a product that contains THC, they may experience symptom relief without feeling “high”. This is especially pertinent for older patients, such as the palliative care patients who make most of the CBD requests, who are trying medical cannabis for the first time and don’t want to feel disoriented.

Globally, in what indications do we see the most research being done?

Dr Ware: Cannabis prohibition has significantly restricted research in terms of access to materials and funding, and this has led to an inability to conduct studies to address important questions of safety and efficacy. The ability to cultivate, produce and develop standardised medical cannabis preparations will allow research to proceed to support therapeutic claims and to inform risk–benefit discussions.

Despite difficulties accessing standardised cannabis products and funding for research, there have been robust attempts to address this research gap. I was part of a team at McGill University that led one of the largest studies looking at the long-term safety of medical cannabis use by patients with chronic pain. The study enrolled more than 400 adults with severe and intractable chronic pain, half of whom used a standardised cannabis product under real-world conditions, and half of whom did not. We observed no difference between groups in serious adverse events, cognitive function, biochemistry, and hematology. Yet over the one-year follow-up period, the cannabis group experienced a significant improvement in their levels of pain, symptom distress, mood, and quality of life.

There is now significant clinical data showing the therapeutic value of medical cannabis, in some cases for symptoms related to pain, mood, and sleep disorders. An expert committee of the National Academies of Sciences, Engineering, and Medicine conducted a systematic review of more than 10,000 papers and found conclusive or substantial evidence that cannabis or cannabinoids are effective treatments for chronic pain, as an antiemetic in chemotherapy-induced nausea and vomiting, and for patient-reported spasticity in MS.

Why is it important to have a well-regulated medical pathway for medical cannabis, especially in markets, like Canada, that have legalised cannabis for adult use?

Dr Ware: Firstly, patients as well their doctors and pharmacists deserve to have access to safe and effective medical cannabis products that are produced in the same way as their other pharmaceutical products. Patients and health professionals need guidance on titration and dosing while ensuring that the levels of the medically important cannabinoids THC and CBD that appear on product labels are accurate and standardised. Cannabis isn’t a one-size-fits-all therapy. It is a complex plant, and people react to it in many different ways. Finding an appropriate product for a patient’s symptoms is often a matter of informed trial and error between the patient and their doctor. Finally, as I mentioned, prohibition has restricted our ability to undertake research. Research conducted thus far has shown a great deal of potential for a wide range of indications and we have only just scratched the surface.



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