Cannabis and pain: it’s complicated

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A new study of 1500 participants, recruited through Australian community pharmacies, has found cannabis may not necessarily be a panacea for pain

Cannabis has been heralded as a potential alternative to opioids in the treatment of pain.

While new research shows the drug may not be all that people hope for, experts say there is a need to look further.

UNSW researchers conducted a four-year prospective cohort study of 1514 people with chronic non-cancer pain prescribed opioids, with the results published this week in The Lancet Public Health.

Participants were recruited through community pharmacies across Australia, and followed up yearly over the study period.

At baseline, 44% of the cohort were male and median age was 58 years. Half (49%) of participants were unemployed and 31% had retired.

Cannabis use was common among participants.

By the fourth year of follow up, 295 (24%) participants had used cannabis for pain.

Interest in using cannabis for pain increased from 364 (33%) participants (at baseline) to 723 (60%) participants (at four years).

At four-year follow up, participants who used cannabis had a greater pain severity score (risk ratio 1·17, 1·03–1·32, for daily or near-daily cannabis use), compared with people with no cannabis use.

Those who used cannabis also had a greater pain interference score (1·14, 1·03–1·26 for daily or near-daily cannabis use), lower pain self-efficacy scores (0·98, 0·96–1·00), and greater generalised anxiety disorder severity scores (1·10, 1·06–1·15).

The authors found no evidence of a relationship between cannabis use and pain severity, and no evidence that cannabis use reduced prescribed opioid use.

“At each assessment, participants who were using cannabis reported greater pain and anxiety, were coping less well with their pain, and reported that pain was interfering more in their life, compared to those not using cannabis,” explains lead author Dr Gabrielle Campbell, from the National Drug and Alcohol Research Centre (NDARC) at UNSW Sydney.

“While this is a large prospective study with high retention over four years, there are a number of caveats to keep in mind.”

“The participants were most likely accessing illicit cannabis … and some of the most common reasons for stopping cannabis use was legal concerns and access difficulties (reported by approximately 20% of participants who reported stopping cannabis use).

“Those using cannabis with the intent of relieving their pain may comprise a patient population with more distress and poorer coping mechanisms as evidenced in our study by the lower pain self-efficacy scores for people who used cannabis.

“It may be that in the absence of cannabis use, pain severity and interference may have been worse. It is difficult to disentangle this based on the current study.”

In a linked comment, Ian Hamilton and Suzanne Gage from the University of York, UK, argue that there is a need for researchers to conduct a randomised controlled trial to gain more definitive results.

“For many patients, their journey to opioid dependency started when they were introduced to these drugs after surgery or as a way of managing acute and chronic pain,” they write.

“There is clearly an incentive to find an alternative drug that has a lower risk of overdose or development of a dependency.

“There are limitations to these observational findings. Although participants were asked about how many days they used cannabis for, we do not know if some people used once in a day or more than once,” they say.

“Likewise, we do not know what type of cannabis the participants used in this study. This fact matters, as cannabis varies in strength and, as with any analgesia, the dose needs to be matched to the severity of pain experienced.

“We should not repeat the problems we now face with opioid prescribing, which originated from weak evidence that these drugs are effective in the management of chronic pain. One way forward would be to conduct a randomised controlled trial to investigate cannabis and its ability to control pain.

“Controlling and measuring the dose and type of cannabis used in such an experiment would be crucial for any comparison study and for applying the findings in practice.”

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