A review found cannabis showed benefits for MS (pain, spasticity), Parkinson's (tremor, pain), ALS (appetite, pain), and Alzheimer's (appetite, sleep, agitation), but worsened bipolar disorder and increased positive symptoms in schizophrenia.
Patients with neurological or psychiatric conditions considering medical cannabis.
Benefits for MS, PD, ALS, and Alzheimer's; risks for schizophrenia and bipolar disorder
What the researchers found
The review examined evidence on cannabis use across six brain disorders, finding a mixed picture that varied dramatically by condition.
Neurological disorders with some benefit: Cannabis reduced pain and spasticity in multiple sclerosis, decreased tremor, rigidity, and pain in Parkinson's disease, and improved quality of life in ALS by helping appetite, pain, and spasticity. In late-stage Alzheimer's, cannabis products improved food intake, sleep quality, and reduced agitation.
Psychiatric disorders with clear risks: Cannabis use was more common among people with schizophrenia than healthy controls. It acted as a risk factor for developing schizophrenia, increased positive symptoms (hallucinations, delusions) in existing patients, though it may have diminished negative symptoms. Cannabis use worsened bipolar disorder with no evidence of benefit.
Across all conditions, the review noted that chronic cannabis use carries risks of cognitive impairment and dependence.
Why it matters
This review provides a condition-by-condition assessment that highlights how the risk-benefit calculation for cannabis varies dramatically depending on the diagnosis. For neurological conditions with pain and spasticity, there appears to be therapeutic value. For psychiatric conditions, particularly schizophrenia and bipolar disorder, the evidence points toward harm.
The numbers in context
Six brain disorders reviewed: ALS, MS, AD, PD, bipolar disorder, schizophrenia. Cannabis use is more prevalent among people with schizophrenia than controls. Bipolar disorder: no evidence of benefit, evidence of worsening. MS: evidence of reduced pain and spasticity. PD: evidence of reduced tremor, rigidity, pain.
How the study worked
Narrative review of published literature on cannabis use in ALS, MS, Alzheimer's disease, Parkinson's disease, bipolar disorder, and schizophrenia.
What this study cannot tell us
Narrative review without systematic methodology. The evidence quality varies dramatically across conditions (stronger for MS, weaker for ALS and AD). Cannabis preparations and doses differed across studies. The review does not distinguish between THC-dominant and CBD-dominant products, which may have very different effects on psychiatric symptoms.
How to read the evidence
Moderate evidence from a narrative review covering multiple conditions with varying evidence quality.
When this study was published
Published in 2017. Research on cannabinoids for neurological and psychiatric conditions continues to evolve.
The bigger picture
The "medical cannabis" narrative often treats cannabis as universally therapeutic. This review demonstrates that the picture is far more nuanced: the same substance that may help a Parkinson's patient with tremor could worsen a schizophrenia patient's hallucinations. Understanding this condition-specificity is essential for informed medical cannabis policy and clinical practice.
Questions still open
- Would CBD-only products be safer for patients with brain disorders who also have psychiatric vulnerability? Should medical cannabis screening include psychiatric assessment to identify patients at risk for worsening? Can the benefits for neurological symptoms be separated from the risks for psychiatric symptoms?
Common questions
Is cannabis safe for people with mental health conditions?
Which brain conditions might benefit from cannabis?
Read the original research
Pros and Cons of Medical Cannabis use by People with Chronic Brain Disorders.
Current neuropharmacology, 15(6), 800-814
Citation
Suryadevara, Uma; Bruijnzeel, Dawn M; Nuthi, Meena; Jagnarine, Darin A; Tandon, Rajiv; Bruijnzeel, Adriaan W. (2017). Pros and Cons of Medical Cannabis use by People with Chronic Brain Disorders.. Current neuropharmacology, 15(6), 800-814. https://doi.org/10.2174/1570159X14666161101095325
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