Cannabis and Chronic Pain: Research Summary

Research Summary: Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort study

WHO?

Research was primarily done by a team at the National Drug and Alcohol Research Centre from the University of New South Wales.

WHAT?

A research project to investigate the use of cannabis and cannabinoids in treating chronic non-cancer pain.  The article was published in The Lancet Public Health and the full text of this paper is available here.

HOW?

The study involved around 1500 participants that were being prescribed opioids (i.e. medication for pain).  These individuals answered a survey at the beginning of the study and then every year for 4 years. 

FACT #1:  Medicinal cannabis is generating a lot of interest around the world for it’s potential use to help manage a range of symptoms in a variety of medical conditions.

FACT #2:   Previous studies have provided some evidence that one of the benefits of medicinal cannabis is reduction in pain. 

FINDING #1:  The most common reasons reported for the use of cannabis in participants were to relieve pain (83% of people using cannabis at the 3 or 4 year time points) and pain-related distress (~70%), improve sleep (~65%) and to help relax (~67%).  The most common reasons for stopping were side-effects (~25%), legal concerns (~22%), difficulty getting access (~19%) and ineffectiveness (~17%).

FINDING #2: At the 2 year, 3 year and 4 year follow-up, people using cannabis gave an average rating of the effectiveness of cannabis for managing their pain as a 7.3, 7.0 and 7.2 out of 10 respectively.

FINDING #3: In all follow-up surveys after baseline, the individuals who were using cannabis had higher average scores for pain severity, pain interference (how much pain gets in the way of everyday life) and anxiety.

THOUGHT:  The study is assessing generalised cannabis use, not medicinal cannabis.  This means that the cannabis used by participants in this study could have large variations in components, which could definitely impact on the effectiveness compared to scientifically synthesised medical grade cannabis. 

THOUGHT:  Participants were not randomly allocated to groups at the beginning of the study, but rather separated into groups based on their initial responses.  This may lead to there being an inherent bias in the data generated.

THOUGHT:  There are limitations to tracking participants through a single survey at the end of each year, especially when using self-reported outcomes.  There is always the possibility that you get individuals on a ‘good pain day’ or a ‘bad pain day’ that may not necessarily be representative of how they have felt for the majority of the previous 12 months.

THOUGHT:  These participants were included in the study based on being prescribed opioids for chronic pain.  However, when assessing an outcome like anxiety, it is known that there can be many contributing factors.  It is difficult to assess a relationship such as cannabis use and anxiety levels without having a full understanding of all of the other issues that may be prevalent in that group.

FINAL THOUGHT:  This study provides some evidence that the role for cannabis in the management of chronic pain is complex and still requires improved understanding, as they found no evidence within their observational cohort of improved outcomes.  As we continue to progress towards understanding how medicinal cannabis may be useful for managing symptoms in many medical conditions, including multiple sclerosis, it is important that we focus on performing well-designed studies and that the outcomes of these trials are reported thoughtfully and accurately.

Whilst this research was reported widely as definitively proving that cannabis has no benefits for chronic pain, I think we need to be very careful about making that sort of conclusion.  Indeed, within the article itself, the researchers note a number of the limitations mentioned above and conclude that 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”.