Medical cannabis or cannabinoids for chronic non-cancer and cancer related pain: a systematic review and meta-analysis of randomised clinical trials

Wang L, Hong PJ, May C et al.

BMJ 2021;373:n1034

Aim of Study

To determine if use of cannabis is superior in chronic pain relief compared to placebo/control groups of usual pain medication through the meta-analysis of randomised controlled clinical trials.

Design and Location

Systematic review and meta-analysis  of randomised controlled trials done internationally.


> Searching for and selection of randomised controlled trials that compare cannabis of any route of administration vs placebo or control group within pre-determined inclusion criteria

> Control groups are medicines usually used for pain relief such as paracetamol, opiodes, or ibuprofen

> Defining outcomes including pain according to standardised pain measurement and definition from International Association for the Study of Pain

> Converting those outcomes into measurement scales

> DerSimonian-Laird method and random-effects models for all meta-analyses

Primary Outcome

Measuring minimal important difference between cannabis and placebo or control group (other pain relief medications in general) in reducing pain.

Secondary Outcomes

Measuring minimal important difference between cannabis and certain other medical pain relief medication usually used such as NSAIDS, paracetamol, or opiods.

Measuring minimal important difference between cannabis and placebo or control group (other pain relief medications) in causing adverse effects including drowsiness, vomiting, nausea, and dizziness.


> 32 studies included in the analysis that use cannabis in test group either in spray form, oral, or topical.

> Minimal evidence of difference in achieving pain relief between Cannabis and placebo or control groups

> 2 RTCs looked into cannabis vs NSAIDs and both were contradictory

> 1 RCT looked into cannabis vs opioids with no difference found

> Higher risk of adverse events, particularly dizziness, in using oral cannabis.


There is minimal difference in chronic pain relief between cannabis and placebo or other types of pain relief.

Stated Limitations from the Study

> Does not include certain forms such as inhaled cannabis due to studies not meeting criteria

> Most trials exclude those who have previous psychological illness and previous cannabis use

> No mention of effect of litigation in use of cannabis which may have effected use of certain cannabis types in the studies and their designs

Discussion from Journal Club Meeting (?Change of Practice)

> Based on this study we may conclude that cannabis does not add to the management of chronic pain patients

> Other limitations of study stated include:

 1) Does not look into different percentages of combinations of chemicals from cannabis – what if those included in the study were not strong enough to achieve the difference?

 2) Does not distinguish between route of adminstration and the form of cannabis administered

 3) Certain effects such as control groups using NSAIDs or Opiods were only one or 2 RCTs – it is difficult to conclude from a meta-analysis of a handful of RCTs

> Other points of discussion: What countries have licensed use of cannabis for pain relief and sedation? How is medical Cannabis used in the under licensing or non-licensing in management of pain.

Summary by Dr S Belal. Journal Club Meeting 5 January 2023.


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