Cannabis use and non-cancer chronic pain
Authors: Iain McGregor
Journal: The Lancet Public Health (2018)

The Article by Gabrielle Campbell and colleagues in The Lancet Public Health (July 2018)1Campbell G Hall WD Peacock A et al.Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort study.Lancet Public Health. 2018; 3: e341-e350Summary Full Text Full Text PDF PubMed Scopus (133) Google Scholar has received worldwide publicity as a demonstration that cannabis is ineffective in treating non-cancer pain. With medicinal cannabis policy in rapid transition, and chronic pain a leading indication for cannabis use,2Lintzeris N Driels J Elias N Arnold JC McGregor IS Allsop DJ Findings from the Cannabis as Medicine Survey (CAMS-16): an online survey of medical cannabis use in Australia.Med J Aust. 2018; 209: 211-216Crossref PubMed Scopus (47) Google Scholar high-quality studies are needed to better inform current debates. Unfortunately, this study1Campbell G Hall WD Peacock A et al.Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort study.Lancet Public Health. 2018; 3: e341-e350Summary Full Text Full Text PDF PubMed Scopus (133) Google Scholar is not one of them. This prospective cohort study involved questioning patients with chronic pain prescribed opioids about their recent use of (illicitly sourced) cannabis. The cannabis users (n=157) were compared with non-users (n=1047) on subjectively reported pain, disability, and anxiety. Although cannabis users reported that the drug was effective in relieving their pain, and despite their >45% reduction in opioid use over 4 years, the authors inferred from their statistical model that cannabis is ineffective in treating pain, and has no opioid-sparing effects. The study is adrift with confounds. Patients with a severe and refractory illness are known to gravitate towards cannabis products.3Suraev A Lintzeris N Stuart J et al.Composition and use of cannabis extracts for childhood epilepsy in the Australian community.Sci Rep. 2018; 8: 10154Crossref PubMed Scopus (39) Google Scholar Indeed, the authors' previous study4Degenhardt L Lintzeris N Campbell G et al.Experience of adjunctive cannabis use for chronic non-cancer pain: findings from the Pain and Opioids IN Treatment (POINT) study.Drug Alcohol Depend. 2015; 147: 144-150Summary Full Text Full Text PDF PubMed Scopus (85) Google Scholar using the same cohort showed that patients who used cannabis were on higher opioid doses for longer than were non-users, with greater pain and poorer function. The inequality in groups at baseline is evident in table 2 of their Article,1Campbell G Hall WD Peacock A et al.Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort study.Lancet Public Health. 2018; 3: e341-e350Summary Full Text Full Text PDF PubMed Scopus (133) Google Scholar but is barely commented upon. The study design did not control for the dosing or formulation of cannabis consumed and allowed no objective confirmation of self-reported cannabis use (or non-use). Some apparent cannabis users could have only been consuming once per month. Given illicit sourcing, it can be assumed that most users are consuming street cannabis containing high concentrations of Δ9-tetrahydrocannabinol via bongs or joints, perhaps even with tobacco.2Lintzeris N Driels J Elias N Arnold JC McGregor IS Allsop DJ Findings from the Cannabis as Medicine Survey (CAMS-16): an online survey of medical cannabis use in Australia.Med J Aust. 2018; 209: 211-216Crossref PubMed Scopus (47) Google Scholar This method of consumption is hardly medicinal, and considering that cannabis has more than 500 bioactive molecules varying greatly across cultivars and preparations, some strains might treat pain better than others. An informative study would involve medically supervised administration of a standardised cannabinoid product within a structured pain management regimen. Such studies, although rare, tend to show medicinal cannabis efficacy in people with chronic pain.5National Academies of Sciences Engineering, and MedicineThe health effects of cannabis and cannabinoids: the current state of evidence and recommendations for research. The National Academies Press, Washington, DC2017Google Scholar Opioid-sparing effects of medicinal cannabis are increasingly apparent from epidemiological data.6Liang D Bao Y Wallace M Grant I Shi Y Medical cannabis legalization and opioid prescriptions: evidence on US Medicaid enrollees during 1993–2014.Addiction. 2018; (published online July 10.)DOI:10.1111/add.14382Crossref PubMed Scopus (48) Google Scholar Finally—it would appear important to note the authors' potential conflicts of interest listed in their Article, which includes links with opioid manufacturers. I currently receive a fellowship from the National Health and Medical Research Council of Australia (NHMRC); research grant funding from the NHMRC, Australian Research Council, and the University of Sydney (Lambert Initiative). I hold patents WO2018107216A1 and WO2017004674A1 licensed to Kinoxis Therapeutics, a patent WO2011038451A1 licensed to Pastorus Pharmaceuticals, and patents AU2017904438, AU2017904072, and AU2018901971 pending. None of these patents relate to pain control. Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort studyCannabis use was common in people with chronic non-cancer pain who had been prescribed opioids, but we found no evidence that cannabis use improved patient outcomes. People who used cannabis had greater pain and lower self-efficacy in managing pain, and there was no evidence that cannabis use reduced pain severity or interference or exerted an opioid-sparing effect. As cannabis use for medicinal purposes increases globally, it is important that large well designed clinical trials, which include people with complex comorbidities, are conducted to determine the efficacy of cannabis for chronic non-cancer pain. Full-Text PDF Open AccessCannabis use and non-cancer chronic pain – Authors' replyIn their letters, Iain McGregor and Alex Bekker state that previous systematic reviews have provided evidence of the effectiveness of cannabinoids for chronic non-cancer pain. However, three systematic reviews1–3 published this year have suggested caution regarding use of cannabinoids, because of a paucity of high quality studies, and concluded that evidence for the effectiveness of cannabinoids in chronic non-cancer pain is limited by the very short duration of studies, small participant numbers, the exclusion of patients with complex comorbidities, and failure of studies to date to include common forms of chronic non-cancer pain (eg, back and neck pain, arthritis). Full-Text PDF Open AccessCannabis use and non-cancer chronic painI read with interest the Article by Gabrielle Campbell and colleagues.1 The authors should be commended on completion of this long prospective study exploring the effect of cannabis on pain outcome measures in patients who used prescribed opioids for the treatment of non-cancer pain. Although the study is thought-provoking, I have noticed a number of potential inconsistencies that require further explanation by the authors. 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