Stockholm Medical Cannabis Conference

A Breakdown of Solmi et al.’s BMJ Umbrella Review regarding harms and benefits of cannabis use

In the groundbreaking study titled “Balancing risks and benefits of cannabis use: umbrella review of meta-analyses of randomised controlled trials and observational studies,” published in the highly prestigious journal BMJ on August 30, researchers employ an umbrella review methodology to offer a comprehensive synthesis of existing evidence on the effects of cannabinoids. This study is particularly timely, given the burgeoning interest in both the medical and recreational use of cannabis.

Utilizing the rigorous GRADE framework, the study scrutinizes the quality of the evidence, thereby lending it a high degree of credibility. The research not only challenges the prevailing legislative approaches to cannabis but also underscores its potential therapeutic benefits. As such, the study holds significant implications for clinicians, policymakers, and the general public, potentially serving as a cornerstone for re-evaluating both clinical and legislative perspectives on cannabis use. The following chart visualises its main findings.


  1. Strengths and Limitations: The study pools evidence from different sources and is the first umbrella review to combine observational and interventional studies on the effects of cannabinoids on humans. However, the evidence should be interpreted cautiously due to variations in tetrahydrocannabinol content among legal and illegally sold cannabis.
  2. Role of Cannabis and Alcohol: The study questions the legislative approaches towards cannabis and alcohol, noting that cannabinoids can have beneficial effects in specific clinical conditions, unlike alcohol. It also highlights the huge discrepancy in Disability-Adjusted Life Years caused by alcohol, compared to cannabis.
  3. Quality of Evidence: The study uses the GRADE framework for assessing the level of evidence, which considers risk of bias, inconsistency, indirectness, imprecision, and publication bias.
  4. Patient and Public Involvement: The study plans to involve patients and the public in the dissemination of its findings, including education of health professionals and policy makers.

What is an Umbrella Review?

An umbrella review is a synthesis of existing meta-analyses and systematic reviews. It aims to provide a comprehensive overview of the evidence across a wide range of studies, both observational and interventional. In essence, it’s like a “meta-meta-analysis,” aggregating already synthesized data of various types to provide the broadest possible perspective.

What is the GRADE system?

The GRADE system (Grading of Recommendations, Assessment, Development, and Evaluations) is a framework used to evaluate the quality of evidence in medical research and to formulate healthcare recommendations. Think of it as a “quality control” checklist for scientific evidence.

Key Components:

  1. Risk of Bias: Assesses how well the study was designed and executed. A well-designed randomized trial has less bias.
  2. Inconsistency: Examines whether the results are similar across different studies. Consistent results are more reliable.
  3. Indirectness: Evaluates how closely the study’s population, interventions, and outcomes align with the question at hand.
  4. Imprecision: Looks at the range of possible outcomes. Narrower ranges are more precise and thus more reliable.
  5. Publication Bias: Considers whether the published studies are a representative sample of all available evidence.

Quality Levels:

  • High: Very confident that the true effect is close to the estimated effect.
  • Moderate: Moderately confident in the effect estimate but there’s a possibility it could be substantially different.
  • Low: Limited confidence in the effect estimate; the true effect could be substantially different.
  • Very Low: Very little confidence in the effect estimate; the true effect is likely to be substantially different.

Editor’s comments:

The study under discussion is a commendable endeavor, employing the umbrella review methodology to synthesize a broad swath of existing meta-analyses and systematic reviews. The utilization of the GRADE framework further bolsters the study’s credibility, providing a rigorous, multi-faceted lens through which the quality of evidence is scrutinized. However, it’s crucial to remember that the robustness of an umbrella review is contingent on the quality of the individual studies it encompasses.

Given the burgeoning interest in cannabinoids for both recreational and medicinal use, the study’s focus is timely and pertinent. It addresses a critical gap in our understanding by juxtaposing the legislative approaches to cannabis and alcohol, thereby challenging the status quo. The study also has the potential to inform not just medical practice but also public policy, making it doubly impactful.

The study’s conclusions, if heeded by medical regulatory authorities, could catalyze a paradigm shift in how we perceive and regulate cannabis. It calls for a nuanced approach that distinguishes cannabis from other substances like alcohol, particularly highlighting its potential therapeutic benefits. This could pave the way for more targeted clinical guidelines and public health campaigns, ultimately fostering a more informed and balanced discourse around cannabis use.

In summary, this study serves as a cornerstone that could significantly influence both clinical practice and legislative frameworks concerning cannabis. Its methodological rigor and topical relevance make it an invaluable addition to the existing body of evidence, warranting serious consideration by clinicians, policymakers, and stakeholders alike.

Stefan Broselid, Ph.D.
Editor-In-Chief, Aurea Care Medical Science Journal


Solmi M, De Toffol M, Kim JY, et al. Balancing risks and benefits of cannabis use: umbrella review of meta-analyses of randomised controlled trials and observational studies. BMJ. 2023;382:e072348. Published 2023 Aug 30. doi:10.1136/bmj-2022-072348