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.
Read this if you want the most authoritative medical society assessment of evidence for cannabinoids in neurological conditions.
Effective for MS spasticity/pain; unknown for epilepsy; nearly 1% serious psychiatric risk
What the researchers 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%.
Why it 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 numbers in context
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 the study worked
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).
What this study cannot 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.
How to read the evidence
Systematic review with formal evidence grading from a major medical society. Gold standard for clinical guideline development.
When this study was published
Published in 2014 and since retired. CBD was later proven effective for specific epilepsies (FDA approved 2018).
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.
Questions still open
- 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?
Common questions
What does the AAN say about medical marijuana?
Is medical marijuana safe for neurological conditions?
Read the original research
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
Citation
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
Explore the wider topic
- CBD Oil Quality Guide: How to Avoid Snake Oil
- Anxiety After Quitting Weed: When to Consider Medication
- Cannabis for Chemotherapy Nausea: What the Evidence Actually Shows
- Cannabis for Chronic Pain: What the Research Actually Supports
- Cannabis and Epilepsy: The Epidiolex Story and What It Means
- Does CBD Actually Work for Anxiety? What the Evidence Shows
- Does CBD Help with Weed Withdrawal? What Studies Show
- CBD vs THC: The Differences That Actually Matter
- The Proven Medical Benefits of Cannabis: What Research Supports
- Quitting Weed Before Surgery
- Weed and Medications: What Changes When You Quit
- Quitting Weed During Pregnancy: What You Need to Know
- Quitting Weed While Pregnant: What You Need to Know
- Cannabis and Older Adults: Risks Seniors Should Know
- Cannabis and Breastfeeding: THC in Breast Milk