Does adding medical cannabis to opioids reduce opioid use for chronic pain? | Research

The takeaway

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.

Anyone evaluating whether medical cannabis can meaningfully reduce opioid dependence for chronic pain, particularly patients and clinicians weighing the evidence.

-3.4 MME opioid change (not significant)

What the researchers 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.

Why it 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 numbers in context

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 the study worked

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.

What this study cannot 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.

How to read the evidence

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.

When this study was published

Published in 2021; newer trials may have updated these findings.

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.

Questions still open

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?

Common 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.

Read the original research

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

View on PubMed ↗Publisher’s paper ↗

Citation

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