American Academy of Neurology systematic review: what medical marijuana evidence actually shows
The AAN found oral cannabis extract effective for MS spasticity and central pain, nabiximols probably effective for spasticity and pain, but cannabinoids probably ineffective for tremor and of unknown efficacy for epilepsy.
Quick Facts
What This Study Found
This systematic review by the American Academy of Neurology evaluated 34 studies (8 Class I) on medical marijuana for neurological conditions. Key findings by indication:
MS Spasticity: Oral cannabis extract was effective; nabiximols and THC were probably effective for patient-reported measures. MS Central Pain: Oral cannabis extract was effective; THC and nabiximols were probably effective. MS Urinary dysfunction: Nabiximols probably effective for reducing bladder voids; THC and oral extract probably ineffective. MS Tremor: THC, oral extract, and nabiximols were probably or possibly ineffective.
For Parkinson's dyskinesias: oral extract was probably ineffective. For Huntington's, Tourette syndrome, cervical dystonia, and epilepsy: oral cannabinoids were of unknown efficacy. The risk of serious psychopathological adverse effects was nearly 1%.
Key Numbers
34 studies reviewed, 8 Class I. Oral cannabis extract: effective for MS spasticity and central pain. Nabiximols: probably effective for spasticity, pain, bladder voids. Serious psychopathological adverse events: nearly 1%.
How They Did This
Systematic review of medical marijuana studies from 1948 to November 2013, graded according to AAN classification for therapeutic evidence. 34 studies met inclusion criteria, 8 were rated Class I (highest quality).
Why This Research Matters
This was the first official systematic review and practice guideline from a major US medical society on medical marijuana. It provided the most authoritative evidence assessment available at the time and influenced clinical practice and policy.
The Bigger Picture
The AAN review established the evidence hierarchy that still largely holds: strongest evidence for MS spasticity and pain, limited or absent evidence for most other neurological conditions. The "unknown efficacy" classification for epilepsy was notable, as this was published before the CBD clinical trials that would later demonstrate efficacy.
What This Study Doesn't Tell Us
The evidence base was limited for most conditions beyond MS. Comparative effectiveness vs. other therapies was unknown. The "unknown efficacy" rating did not mean ineffective, just unstudied. The review has since been retired, potentially reflecting evolved evidence.
Questions This Raises
- ?Has the evidence changed enough since 2014 to warrant updated recommendations?
- ?Why was the review retired?
- ?Would inclusion of CBD epilepsy trial data change the overall assessment?
Trust & Context
- Key Stat:
- Effective for MS spasticity/pain; unknown for epilepsy; nearly 1% serious psychiatric risk
- Evidence Grade:
- Systematic review with formal evidence grading from a major medical society. Gold standard for clinical guideline development.
- Study Age:
- Published in 2014 and since retired. CBD was later proven effective for specific epilepsies (FDA approved 2018).
- Original Title:
- Systematic review: efficacy and safety of medical marijuana in selected neurologic disorders [RETIRED]: report of the Guideline Development Subcommittee of the American Academy of Neurology.
- Published In:
- Neurology, 82(17), 1556-63 (2014)
- Authors:
- Koppel, Barbara S, Brust, John C M, Fife, Terry, Bronstein, Jeff, Youssof, Sarah, Gronseth, Gary, Gloss, David
- Database ID:
- RTHC-00817
Evidence Hierarchy
Analyzes all available research on a topic using a structured method.
What do these levels mean? →Frequently Asked Questions
What does the AAN say about medical marijuana?
This 2014 review found the strongest evidence for MS spasticity and central pain (oral cannabis extract rated effective). Evidence was insufficient for epilepsy, Tourette syndrome, and most movement disorders. Note: the review predates CBD epilepsy trials.
Is medical marijuana safe for neurological conditions?
The review found a nearly 1% risk of serious psychopathological adverse effects. Common side effects were similar to other CNS-active drugs. The risk-benefit balance favored use primarily for MS spasticity and pain.
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Cite This Study
https://rethinkthc.com/research/RTHC-00817APA
Koppel, Barbara S; Brust, John C M; Fife, Terry; Bronstein, Jeff; Youssof, Sarah; Gronseth, Gary; Gloss, David. (2014). Systematic review: efficacy and safety of medical marijuana in selected neurologic disorders [RETIRED]: report of the Guideline Development Subcommittee of the American Academy of Neurology.. Neurology, 82(17), 1556-63. https://doi.org/10.1212/WNL.0000000000000363
MLA
Koppel, Barbara S, et al. "Systematic review: efficacy and safety of medical marijuana in selected neurologic disorders [RETIRED]: report of the Guideline Development Subcommittee of the American Academy of Neurology.." Neurology, 2014. https://doi.org/10.1212/WNL.0000000000000363
RethinkTHC
RethinkTHC Research Database. "Systematic review: efficacy and safety of medical marijuana ..." RTHC-00817. Retrieved from https://rethinkthc.com/research/koppel-2014-systematic-review-efficacy-and
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.