Does adding medical cannabis to opioids reduce opioid use for chronic pain?
A systematic review and meta-analysis found very low certainty evidence that medical cannabis reduces opioid use, and high certainty evidence from RCTs that it had little effect on pain or sleep in chronic cancer pain patients.
Quick Facts
What This Study Found
Randomized trials (all in cancer pain) found adding cannabis had little or no impact on opioid dose (weighted mean difference: -3.4 MME, 95% CI -12.7 to 5.8) or pain relief (-0.18 cm on 10 cm VAS). Cannabis addition likely increased nausea (RR 1.43) and vomiting (RR 1.50). Observational studies suggested a larger opioid reduction (-22.5 MME) but with very low certainty.
Key Numbers
5 RCTs + 12 observational studies; opioid change in RCTs: -3.4 MME (not significant); pain relief: -0.18 cm on 10 cm VAS (not clinically meaningful); nausea risk ratio: 1.43; vomiting risk ratio: 1.50; observational opioid reduction: -22.5 MME (very low certainty)
How They Did This
Systematic review and meta-analysis searching CENTRAL, EMBASE, and MEDLINE. Included 5 randomized trials (all chronic cancer pain) and 12 observational studies. Evidence certainty assessed using GRADE framework.
Why This Research Matters
The idea that cannabis can replace opioids is popular in public discourse. This rigorous analysis suggests the opioid-sparing effect remains unproven, with the strongest evidence showing little benefit and increased side effects.
The Bigger Picture
The gap between observational and randomized data is notable. Patients who self-select cannabis may differ in ways that inflate apparent benefits. Until higher-quality trials are conducted outside cancer pain populations, the opioid-sparing narrative lacks solid footing.
What This Study Doesn't Tell Us
All RCTs enrolled cancer pain patients, limiting generalizability. RCTs instructed participants to maintain opioid doses, making it difficult to detect dose reduction. Observational studies had very low certainty evidence.
Questions This Raises
- ?Would results differ in non-cancer chronic pain populations?
- ?Could trials designed to allow opioid tapering show different outcomes?
- ?Does cannabis type (THC vs CBD dominant) matter for opioid-sparing effects?
Trust & Context
- Key Stat:
- -3.4 MME opioid change (not significant)
- Evidence Grade:
- Meta-analysis using GRADE framework. RCT evidence rated high certainty for pain outcomes but very low certainty for opioid reduction due to study design constraints.
- Study Age:
- Published in 2021; newer trials may have updated these findings.
- Original Title:
- Opioid-sparing effects of medical cannabis or cannabinoids for chronic pain: a systematic review and meta-analysis of randomised and observational studies.
- Published In:
- BMJ open, 11(7), e047717 (2021)
- Authors:
- Noori, Atefeh, Miroshnychenko, Anna, Shergill, Yaadwinder, Ashoorion, Vahid, Rehman, Yasir, Couban, Rachel J, Buckley, D Norman, Thabane, Lehana, Bhandari, Mohit, Guyatt, Gordon H, Agoritsas, Thomas, Busse, Jason W
- Database ID:
- RTHC-03386
Evidence Hierarchy
Combines results from multiple studies to find an overall pattern.
What do these levels mean? →Frequently Asked Questions
Does cannabis help people use fewer opioids?
The strongest evidence (from randomized trials) did not show a significant reduction in opioid use when cannabis was added. Observational studies suggested some reduction, but that evidence was rated very low certainty.
Why did observational studies show bigger effects than RCTs?
Observational studies are prone to confounding: patients who choose cannabis may already be reducing opioids, have different pain levels, or differ in other ways that inflate apparent benefits.
Did cannabis help with pain at all?
In the randomized trials, the pain reduction (-0.18 cm on a 10 cm scale) was not clinically meaningful. The minimally important difference is generally considered to be 1 cm.
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Cite This Study
https://rethinkthc.com/research/RTHC-03386APA
Noori, Atefeh; Miroshnychenko, Anna; Shergill, Yaadwinder; Ashoorion, Vahid; Rehman, Yasir; Couban, Rachel J; Buckley, D Norman; Thabane, Lehana; Bhandari, Mohit; Guyatt, Gordon H; Agoritsas, Thomas; Busse, Jason W. (2021). Opioid-sparing effects of medical cannabis or cannabinoids for chronic pain: a systematic review and meta-analysis of randomised and observational studies.. BMJ open, 11(7), e047717. https://doi.org/10.1136/bmjopen-2020-047717
MLA
Noori, Atefeh, et al. "Opioid-sparing effects of medical cannabis or cannabinoids for chronic pain: a systematic review and meta-analysis of randomised and observational studies.." BMJ open, 2021. https://doi.org/10.1136/bmjopen-2020-047717
RethinkTHC
RethinkTHC Research Database. "Opioid-sparing effects of medical cannabis or cannabinoids f..." RTHC-03386. Retrieved from https://rethinkthc.com/research/noori-2021-opioidsparing-effects-of-medical
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.