Cannabis medicines improved some mental disorder symptoms but achieved no remissions in systematic review | Research

The takeaway

A systematic review of 14 RCTs found THC- and CBD-based medicines improved some symptoms across multiple mental disorders when added to standard treatment, but did not produce remission, and the evidence base remains too small for reliable recommendations.

People considering cannabis for mental health conditions, clinicians, and anyone wanting the evidence-based perspective on cannabinoid psychiatry.

14 RCTs, 1,629 patients: symptom improvements but zero remissions across mental disorders

What the researchers found

Across 14 RCTs (1,629 participants) covering dementia, cannabis/opioid dependence, psychosis, social anxiety, PTSD, anorexia nervosa, ADHD, and Tourette's disorder, cannabis-based medicines as adjuncts were associated with symptom improvements but not remission. Severe adverse effects were rare.

Why it matters

This provides a reality check on cannabis for mental health. Improvements were seen, but no condition achieved remission, and sample sizes remain small. The gap between popular enthusiasm for cannabis as a mental health treatment and the evidence base is clear.

The numbers in context

14 RCTs, 1,629 participants. Diagnoses: dementia, cannabis/opioid dependence, psychosis/schizophrenia, social anxiety, PTSD, anorexia nervosa, ADHD, Tourette's. Improvements in several symptoms. No remission achieved. Severe adverse effects in single cases only.

How the study worked

Review of systematic reviews and RCTs searching five databases (2006-August 2018). Four systematic reviews (of 11 RCTs) and 14 RCTs with 1,629 participants were included. Narrative synthesis due to heterogeneous outcomes. Risk of bias and SIGN checklists applied.

What this study cannot tell us

Too heterogeneous for meta-analysis. Small trial sizes across all conditions. Many different THC/CBD formulations and doses used. Adjunctive use only (added to existing treatment), not standalone. Short follow-up periods in most trials.

How to read the evidence

Moderate: systematic methodology covering RCTs only, but limited by small trial sizes and heterogeneous outcomes.

When this study was published

Published in 2019, covering studies through August 2018.

The bigger picture

Cannabis-based medicines may be useful adjuncts rather than standalone treatments for mental disorders. The field needs much larger, more rigorous trials with standardized outcomes before treatment recommendations can be made with confidence.

Questions still open

Which specific mental disorders are most likely to benefit from cannabinoid adjunctive therapy? Would larger trials confirm the improvements seen in these small studies? What dosing and formulation would be optimal for each condition?

Common questions

Can cannabis treat mental health conditions?

This systematic review found cannabis-based medicines improved some symptoms across multiple conditions including anxiety, PTSD, and psychosis when added to standard treatment. However, no condition achieved remission, and the evidence base is too small for firm recommendations.

Is cannabis safe for mental health use?

Across 14 trials with 1,629 participants, severe adverse effects were mentioned in single cases only. Side effects occurred but were generally manageable. However, long-term safety data for psychiatric use remain limited.

Read the original research

How effective and safe is medical cannabis as a treatment of mental disorders? A systematic review.

European archives of psychiatry and clinical neuroscience, 269(1), 87-105

View on PubMed ↗Publisher’s paper ↗

Citation

Hoch, Eva; Niemann, Dominik; von Keller, Rupert; Schneider, Miriam; Friemel, Chris M; Preuss, Ulrich W; Hasan, Alkomiet; Pogarell, Oliver. (2019). How effective and safe is medical cannabis as a treatment of mental disorders? A systematic review.. European archives of psychiatry and clinical neuroscience, 269(1), 87-105. https://doi.org/10.1007/s00406-019-00984-4