What We Really Know About Medical Cannabis: A Review of Reviews
What Researchers Found About Chronic Pain and Cannabis
The Study at a Glance
Published
Canadian Family Physician, 2018
Researchers
Multiple institutions (Canada)
Study Type
Systematic ReviewDuration
N/A (review of reviews)
Key Finding
There is reasonable evidence that cannabinoids improve nausea and vomiting after chemotherapy. They might improve spasticity. There is uncertainty about whether they improve pain, but if they do, it is neuropathic pain and the benefit is likely small. Adverse effects are very common.
Key Finding: There is reasonable evidence that cannabinoids improve nausea and vomiting after chemotherapy. They might improve spasticity. There is uncertainty about whether they improve pain, but if they do, it is neuropathic pain and the benefit is likely small. Adverse effects are very common.
What Researchers Studied About Chronic Pain and Cannabis
This is a "review of reviews" that examined the highest-level evidence on medical cannabinoids.
Researchers searched MEDLINE, the Cochrane Database, and references of included studies.
They included systematic reviews with 2 or more randomized controlled trials focusing on pain, spasticity, or nausea/vomiting. For adverse events, any meta-analysis was included.
How This Systematic Review Was Conducted
The researchers synthesized findings from multiple systematic reviews to determine what we actually know about cannabinoid effectiveness.
They examined evidence for three main conditions: 1. Nausea and vomiting after chemotherapy 2. Spasticity (primarily in multiple sclerosis) 3. Pain (various types)
They also reviewed meta-analyses examining adverse events from cannabinoid use.
Chronic Pain Treatment Results
The Main Results:
- 1NAUSEA/VOMITING: "Reasonable evidence" cannabinoids improve chemotherapy-induced symptoms
- 2SPASTICITY: Cannabinoids "might improve" spasticity, primarily in multiple sclerosis
- 3PAIN: "Some uncertainty" whether cannabinoids improve pain
- 4PAIN (if effective): Limited to neuropathic pain, benefit likely small
- 5ADVERSE EFFECTS: "Very common" across all cannabinoid treatments
- 6CONCLUSION: Benefits would need to be considerable to warrant trials of therapy
By the Numbers
| Statistic | What It Means |
|---|---|
| Reasonable | Evidence level for cannabinoids improving chemotherapy nausea/vomiting |
| Uncertain | Evidence level for cannabinoids improving pain |
| Small | Expected benefit size for neuropathic pain, if any benefit exists |
| Very common | Frequency of adverse effects with cannabinoid treatments |
Evidence level for cannabinoids improving chemotherapy nausea/vomiting
Evidence level for cannabinoids improving pain
Expected benefit size for neuropathic pain, if any benefit exists
Frequency of adverse effects with cannabinoid treatments
What This Means for Chronic Pain Patients
This high-level review summarizes what we actually know from the best available evidence on medical cannabis.
For chemotherapy-related nausea and vomiting, there is reasonable evidence cannabinoids help. This is the strongest finding.
For spasticity (muscle stiffness), particularly in multiple sclerosis, cannabinoids might help but the evidence is not as strong.
For pain, there is uncertainty. If cannabinoids do help pain, it is specifically neuropathic (nerve) pain, and the benefit is likely small.
Importantly, adverse effects are very common with cannabinoids. The authors note that "benefits would need to be considerable to warrant trials of therapy."
This does not mean cannabis never helps, but it does mean the evidence is more limited than popular claims suggest.
Quick Answers: Chronic Pain and Cannabis
Direct answers based on the findings of this study:
Research Summary: Answers are based on published peer-reviewed studies and represent research findings, not medical recommendations. Individual results may vary. Always consult a healthcare provider before making treatment decisions.
What does research actually say about medical marijuana?
Reasonable evidence for chemo nausea, possible for MS spasticity. A 2018 review of reviews found uncertain evidence for pain (if any benefit, limited to nerve pain and small). Adverse effects are very common.
Source: Allan et al., Canadian Family Physician, 2018 (PMID: 29449262)
Is there good evidence cannabis helps pain?
Evidence is uncertain. A high-level review found "some uncertainty about whether cannabinoids improve pain." If they do help, it is specifically neuropathic (nerve) pain, and "the benefit is likely small."
Source: Allan et al., Canadian Family Physician, 2018 (PMID: 29449262)
How common are cannabis side effects?
Very common. A review of systematic reviews found adverse effects from cannabinoids are "very common," leading the authors to conclude that "benefits would need to be considerable to warrant trials of therapy."
Source: Allan et al., Canadian Family Physician, 2018 (PMID: 29449262)
This is educational content, not medical advice
The research summarized here is for informational purposes only. Individual results may vary, and what works in studies may not work the same way for everyone. Always consult with a qualified healthcare provider before making changes to your treatment plan or starting medical cannabis therapy.
Important Limitations
This study has some caveats to keep in mind when interpreting the results:
- This is a review of reviews, not primary data
- Evidence strength varies by condition
- Does not include studies published after the search date
- Adverse events are very common across all uses
- Cannot account for individual variation in response
The Bottom Line on Cannabis for Chronic Pain
This "review of reviews" summarizes the highest-level evidence: reasonable evidence supports cannabinoids for chemotherapy nausea/vomiting. They might help MS spasticity. For pain, evidence is uncertain, and if effective, it is limited to neuropathic pain with small benefits. Adverse effects are very common. Benefits would need to be considerable to justify treatment trials.
Do You Qualify for Medical Marijuana?
If you're living with Chronic Pain, you may qualify for a medical marijuana card. Our licensed physicians can evaluate you from home via telehealth.
Related Research & Resources
Related Research
Get Your Card
This condition qualifies for medical marijuana in:
Source
Allan GM, Finley CR, Ton J, et al. "Systematic review of systematic reviews for medical cannabinoids: Pain, nausea and vomiting, spasticity, and harms" Canadian Family Physician. 2018.
Important Information
Study Age: This study was published 8 years ago. Newer research may have updated or refined these findings.
Not Medical Advice: This research summary is for educational purposes only. It should not be used to diagnose, treat, cure, or prevent any disease or medical condition. Always consult a qualified healthcare provider before starting or changing any treatment.
Individual Variation: Research findings represent group averages. Your individual response to cannabis may differ based on genetics, other medications, underlying conditions, and many other factors.
Last reviewed: January 25, 2026
Important Notices
Research Summary Disclaimer
This content represents our interpretation of published scientific research for educational purposes. It should not be used to make treatment decisions without consulting a qualified healthcare provider. Individual results may vary from study findings.
FDA Notice
These statements have not been evaluated by the FDA. Cannabis is not intended to diagnose, treat, cure, or prevent any disease. The FDA has not approved cannabis for any medical condition except specific prescription medications.
Copyright & Fair Use
Research summaries are provided under fair use (17 U.S.C. § 107) for educational purposes. We provide brief summaries with attribution, not full reproductions. All studies remain the intellectual property of their respective authors and publishers.
Data Sources
Study information sourced from PubMed®, U.S. National Library of Medicine. Inclusion does not imply endorsement by NLM, NIH, or the federal government.
For complete information, see our Terms of Use and Research Content Policy.
FAQs: Cannabis for Chronic Pain
What conditions does medical cannabis actually help?
Reasonable evidence for chemo nausea, possible for MS spasticity, uncertain for pain. According to this review of reviews, if cannabis helps pain, it is limited to nerve pain with small benefits. Adverse effects are very common.
Does cannabis help with pain?
Uncertain, possibly small benefit for nerve pain. This high-level review found "some uncertainty about whether cannabinoids improve pain, but if they do, it is neuropathic pain and the benefit is likely small."
Are there side effects from medical cannabis?
Yes. This review found adverse effects are "very common" with cannabinoid treatments. The authors note that benefits would need to be considerable to warrant trials of therapy given the frequency of side effects.