A review of 72 reviews on medical cannabis found mixed results and mostly low-quality evidence
A scoping review of 72 systematic reviews on medical cannabis found mostly mixed or inconclusive results, with only one review rated as high quality. Mild harms were frequently reported and may outweigh benefits.
Quick Facts
What This Study Found
Pain management was the most commonly studied condition. A small number of reviews found benefits for pain, but analysis quality varied widely. Adverse effects were reported in 83% of reviews comparing cannabis to placebo and 83% comparing to active drugs. Minor harms (drowsiness, dizziness) were common. Serious harms were reported in 36% of reviews. Only 1 of 72 reviews was rated high quality; 36 were moderate, 35 were low/critically low.
Key Numbers
1,975 citations screened. 72 systematic reviews included. 1/72 rated high quality. 36 moderate quality. 35 low/critically low quality. Adverse effects in 83% of reviews vs. placebo. Serious harms in 36% of those reviews.
How They Did This
Scoping review of systematic reviews from multiple databases. Two reviewers selected and charted data from 72 included systematic reviews covering various medical conditions.
Why This Research Matters
This is a review of reviews, providing a bird's-eye view of the entire medical cannabis evidence base. The finding that 71 of 72 reviews were not high quality is a damning assessment of the field's evidence standards.
The Bigger Picture
Medical cannabis has gained enormous cultural and legal acceptance, but this comprehensive overview reveals that the scientific evidence supporting it remains remarkably weak. The field needs rigorous, well-designed clinical trials.
What This Study Doesn't Tell Us
Scoping review methodology provides a broad overview but does not synthesize quantitative results. The quality of included reviews varied dramatically. The review was limited to systematic reviews, potentially missing primary research.
Questions This Raises
- ?Why is the quality of cannabis research so low?
- ?Are regulatory barriers preventing better studies?
- ?Would the results change if only high-quality evidence were considered?
- ?Which specific conditions have the strongest evidence?
Trust & Context
- Key Stat:
- Only 1 of 72 systematic reviews was rated high quality
- Evidence Grade:
- Moderate: scoping review of 72 systematic reviews provides broad evidence synthesis, but the underlying evidence quality was mostly poor.
- Study Age:
- Published in 2019.
- Original Title:
- Benefits and harms of medical cannabis: a scoping review of systematic reviews.
- Published In:
- Systematic reviews, 8(1), 320 (2019)
- Authors:
- Pratt, Misty, Stevens, Adrienne, Thuku, Micere, Butler, Claire, Skidmore, Becky, Wieland, L Susan, Clemons, Mark, Kanji, Salmaan, Hutton, Brian
- Database ID:
- RTHC-02239
Evidence Hierarchy
Maps out the available research on a broad question.
What do these levels mean? →Frequently Asked Questions
Does this mean medical cannabis doesn't work?
Not necessarily. The review found that most existing research is too low-quality to draw firm conclusions either way. A small number of reviews did find benefits for pain, but the overall evidence base is weak.
What were the most common side effects?
Drowsiness and dizziness were the most frequently reported. Serious harms were less common but appeared in over a third of the reviews that reported on adverse effects.
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Cite This Study
https://rethinkthc.com/research/RTHC-02239APA
Pratt, Misty; Stevens, Adrienne; Thuku, Micere; Butler, Claire; Skidmore, Becky; Wieland, L Susan; Clemons, Mark; Kanji, Salmaan; Hutton, Brian. (2019). Benefits and harms of medical cannabis: a scoping review of systematic reviews.. Systematic reviews, 8(1), 320. https://doi.org/10.1186/s13643-019-1243-x
MLA
Pratt, Misty, et al. "Benefits and harms of medical cannabis: a scoping review of systematic reviews.." Systematic reviews, 2019. https://doi.org/10.1186/s13643-019-1243-x
RethinkTHC
RethinkTHC Research Database. "Benefits and harms of medical cannabis: a scoping review of ..." RTHC-02239. Retrieved from https://rethinkthc.com/research/pratt-2019-benefits-and-harms-of
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.