Medical cannabis or cannabinoids for chronic pain: a clinical practice guideline

Dear Editor,

We commend the authors Busse et al for their efforts in evaluating the evidence regarding medical cannabis for chronic pain and translating these findings into a clinical guideline. There is a great paucity of information available in this area, and efforts such as this are greatly needed to guide clinicians in managing cannabis in this patient population. Upon review of the guideline, we were concerned to see that the route of inhalation was not included. While we acknowledge some of the highest-grade evidence focuses on oral cannabis consumption, this does not reflect what is seen in real-world clinical practice. A recent 2020 Statistics Canada survey reported 74% of those who use cannabis inhale (smoke or vaporize) dried flower versus 25% who consume oil (1) . Accordingly, in clinical practice, we are still seeing a large proportion of patients using inhalation to control both chronic, and especially acute pain symptoms. Here, we wish to provide insights as to why we believe this modality should be included in future clinical practice guidelines.

Inhalation does not necessarily indicate recreational use, and has medical utility for many patients. Inhaled cannabis is effective for controlling acute symptoms and is more accessible for many patients due to lower cost. Evidence from several short and long-term, high-quality studies support the utility of inhaled cannabis for controlling pain symptoms (e.g. 2, 3). We also know that each route of cannabis administration has unique pharmacokinetic properties impacting the onset and duration of action. The short onset and duration of action of inhalation can be advantageous in managing acute, breakthrough pain. Inhalation allows clinicians to customize the route of administration to best meet the needs of the patient with chronic pain. Clinically, patients often use multiple methods of cannabis administration to manage their condition. This approach to pain management is common with opioid use, where long-acting products (i.e. oral cannabis) is used to manage background pain, where short-acting products (i.e. inhaled cannabis) is used for breakthrough pain. Although we acknowledge the potential harm of smoked cannabis, vaporization greatly decreases risk of respiratory harm. Furthermore, the shorter duration of action also reduces the time of potential impairment or adverse events.

We also feel that vaporization is an important harm reduction tool for those who smoke cannabis. Clinically, we observe transitioning patients immediately to oil from smoking is challenging for the patient due to habit, committing to a longer onset of action, and determining equivalent doses for oral format. We have had much greater success when switching patients from smoked cannabis to vaporization as the first harm reduction strategy. Several high-quality studies have suggested vaporization of regulated products is safe and associated with significantly less harm than smoking (4, 5). Given the high prevalence of cannabis smoking, the known harms, and that many patients will begin their medical cannabis journey smoking cannabis, vaporization is an important harm reduction strategy.

Finally, vaporization is important for accessibility. Oils are considerably more expensive than dried flower and are simply not an option for some patients. This is especially important given the high rates of medical cannabis patients on disability or in low-income situations. Vaporization is also cost saving over smoking. Cannabis vapor has a higher cannabinoid to by-product ratio than cannabis smoke (4, 6). Further, vaporization does not have the loss of side stream smoke that occurs with smoking. Together, these factors make vaporization more efficient, hence it being more cost-effective as less product needs to be used. Although there is an initial cost for the vaporizer, it is still one of the most cost-effective options over the long-term.

Given the above points, there is potential harm in not including inhalation within clinical practice guidelines. We worry clinicians will take this guideline to mean there is no evidence for inhalation and that it should not be used. This may inadvertently stigmatize a large group of current medical cannabis users. We aim to highlight that there is good evidence for both the efficacy and safety of vaporization and that it is an important clinical tool for harm reduction. We maintain that the authors of this piece provided an important first step in furthering the guidance for this area. Moving forward, we emphasize the importance of engaging in research that matches real-world practice and includes common patient demographics, such as those on disability, veterans, with mental health challenges, and using multiple routes of administration.

1. Health Canada. (2021). Canadian Cannabis Survey 2020: Summary. Government of Canada. https://www.canada.ca/en/health-canada/services/drugs-medication/cannabi...
2. Ware, M. A., Wang, T., Shapiro, S., Collet, J. P., & COMPASS study team (2015). Cannabis for the Management of Pain: Assessment of Safety Study (COMPASS). The journal of pain, 16(12), 1233–1242. https://doi.org/10.1016/j.jpain.2015.07.014
3. Andreae, M. H., Carter, G. M., Shaparin, N., Suslov, K., Ellis, R. J., Ware, M. A., Abrams, D. I., Prasad, H., Wilsey, B., Indyk, D., Johnson, M., & Sacks, H. S. (2015). Inhaled Cannabis for Chronic Neuropathic Pain: A Meta-analysis of Individual Patient Data. The journal of pain, 16(12), 1221–1232. https://doi.org/10.1016/j.jpain.2015.07.009
4. Abrams, D. I., Vizoso, H. P., Shade, S. B., Jay, C., Kelly, M. E., & Benowitz, N. L. (2007). Vaporization as a smokeless cannabis delivery system: a pilot study. Clinical pharmacology and therapeutics, 82(5), 572–578. https://doi.org/10.1038/sj.clpt.6100200
5. Gieringer, D., St. Laurent, J., Goodrich, S. (2004). Cannabis Vaporizer Combines Efficient Delivery of THC with Effective Suppression of Pyrolytic Compounds. Journal of Cannabis Therapeutics, 4:1, 7-27. https://doi.org/10.1300/J175v04n01_02
6. Pomahacova, B., Van der Kooy, F., Verpoorte, R. (2009). Cannabis smoke condensate III: The cannabinoid content of vaporised Cannabis sativa, Inhalation Toxicology, 21:13, 1108-1112, https://doi.org/ 10.3109/08958370902748559