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

I read with interest the Article by Gabrielle Campbell and colleagues.1Campbell G Hall W 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 (127) Google Scholar 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. The study results are based on phone interviews of cannabis users (78 occasional and 48 nearly daily cannabis users at baseline, out of a total sample of 1514 participants). The majority of participants used illicitly obtained cannabis without knowing its content. On the basis of this sample, the authors report that the patients using cannabis had increased pain and generalised anxiety disorder severity scores, compared with those not using cannabis. The use of cannabis did not reduce prescribed opioid requirements. At the same time, the authors found that the participants who used cannabis also reported that cannabis had been effective with regard to pain reduction (mean score of 7·3 at 2-year, 7·0 at 3-year, and 7·2 at 4-year follow-up, with 10 being a complete relief). In fact, 60% of the participants at the 4-year follow-up would have used cannabis if they had access to it, versus 33% at baseline. Moreover, the cannabis users claimed that they used cannabis for the following reasons: to alleviate pain (83% at 3-year follow-up and 83% at 4-year follow-up), to reduce pain-related distress (68% and 73%, respectively), to improve sleep (67% and 64%), and to reduce generalised anxiety (72% and 65%). Only 22% of participants at 3 years and 12% at 4 years reported that they had discontinued using cannabis because of the ineffectiveness of the substance in relieving pain. Finally, 22% of participants at 3 years and 30% at 4 years reported reduced opioid requirements when using cannabis. The authors do not provide the characteristics of these participants. Numerous studies, including systematic reviews and meta-analyses, have documented the salutary effects of cannabis and cannabinoids in the treatment of chronic pain of non-cancer origin.2Aviram J Samuelly-Leichtag G Efficacy of cannabis-based medicines for pain management: a systematic review and meta-analysis of randomized controlled trials.Pain Physician. 2017; 20: E755-E796Crossref PubMed Google Scholar, 3Whiting P Wolff R Deshpande S et al.Cannabinoids for medical use: a systematic review and meta-analysis.JAMA. 2015; 313: 2456-2473Crossref PubMed Scopus (1325) Google Scholar Two well-conducted studies corroborate these conclusions (ie, a reduction in opioid prescribing).4Bradford A Bradford D Abraham A et al.Association between US State medical cannabis laws and opioid prescribing in the Medicare Part D population.JAMA Intern Med. 2018; 178: 667-673Crossref PubMed Scopus (132) Google Scholar, 5Wen H Hockenberry J Association of medical and adult-use marijuana laws with opioid prescribing for medical enrollees.JAMA Intern Med. 2018; 178: 673-679Crossref PubMed Scopus (124) Google Scholar Therefore, the authors should discuss the discordant results and possible reasons for the contradictions. Some studies have suggested that cannabis might preferentially target the affective aspects of pain and that cannabinoids induce anti-anxiety effects.6Lee M Ploner M Wiech K et al.Amygdala activity contributes to the dissociative effect of cannabis on pain perception.Pain. 2013; 154: 124-134Summary Full Text Full Text PDF PubMed Scopus (91) Google Scholar, 7Fusar-Poli P Grippa J Bhattacharyya S et al.Distinct effect of delta-9-tetrahydrocannabinol and cannabidiol on neural activation during emotional processing.Arch Gen Psychiatry. 2009; 66: 95-105Crossref PubMed Scopus (346) Google Scholar One of the beneficial mechanisms of cannabis use for pain disorders could be related to its ability to alter the reactive thoughts regarding negative feelings associated with pain. Thus, cannabinoids might positively affect a patient's perception of pain and improve coping mechanisms. The disassociation of objectively measured pain outcomes from the perception of pain by the participants might explain the contradictory results. I declare no competing interests. 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 painThe Article by Gabrielle Campbell and colleagues in The Lancet Public Health (July 2018)1 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,2 high-quality studies are needed to better inform current debates. Unfortunately, this study1 is not one of them. Full-Text PDF Open Access