🟠 Moderate Evidence
A comprehensive systematic review published in The Lancet Psychiatry analysing 54 randomized controlled trials involving 2,477 participants found minimal evidence supporting cannabis use for most psychiatric conditions. The review, which examined data spanning 1980 to 2025, identified only three areas where cannabinoids showed meaningful effects: cannabis use disorder itself, device-measured sleep time in insomnia, and tic severity in Tourette’s syndrome.
Key takeaways
- No significant benefit demonstrated for anxiety, PTSD, psychosis, or opioid use disorder compared to placebo
- Depression—one of the top reasons patients are prescribed cannabis—has never been tested in a controlled trial
- Cannabis users were 75% more likely to experience adverse events than placebo users
- 27% of adults aged 16–65 in the US and Canada report medical cannabis use, with approximately half citing mental health reasons
Evidence certainty for cannabis in nine psychiatric conditions
Systematic review of 54 RCTs (1980–2025); GRADE-assessed outcomes
Source: The Lancet Psychiatry (2025) | Georgian Medical Journal News
Evidence gaps for the most commonly prescribed conditions
The review identified a critical evidence void: depression, consistently cited as a primary reason for medical cannabis prescription, has not been evaluated in any randomized controlled trial to date. According to The Lancet Psychiatry analysis, confidence intervals for anxiety, PTSD, psychosis, and opioid use disorder all crossed the null line, indicating no statistically significant difference from placebo across their primary outcomes. This represents a fundamental mismatch between clinical practice and the evidence base underpinning regulatory approval in multiple jurisdictions.
The regulatory framework has approved cannabis products for medical use in more than a dozen US states as a qualifying treatment for PTSD, yet the systematic review found no rigorous evidence supporting this indication. This pattern—where regulatory approval preceded clinical trial evidence—raises questions about the foundational evidence supporting current prescribing patterns across psychiatric indications, particularly for conditions affecting millions of users.
Where evidence does exist, efficacy remains limited
The most robust findings from the Lancet Psychiatry review emerged in three specific areas. For insomnia, device-measured sleep time showed a moderate-certainty benefit—the only moderate-certainty finding across the entire analysis. In Tourette’s syndrome, cannabinoid combinations (CBD and THC together) produced measurable reductions in tic severity, though the evidence grade remained low. For cannabis use disorder itself, the review found evidence that cannabinoids reduced consumption, though this represents treating the disorder with the same substance causing it.
Autistic trait reduction appeared in the data, but both contributing studies carried high risk of bias, limiting confidence in the finding. One unexpected result moved in the opposite direction: cannabinoids increased cocaine craving compared to placebo, a signal that warrants further investigation given the overlap between cannabis and opioid use disorder populations.
For every 7 people treated with cannabinoids for psychiatric conditions, 1 experienced an adverse event that would not have occurred with placebo, according to the comprehensive analysis published in The Lancet Psychiatry.
— Systematic review of 54 RCTs (1980–2025), The Lancet Psychiatry (2025)
Regulatory approval outpaced clinical evidence
According to the review, approximately 27% of adults aged 16 to 65 in the United States and Canada report using cannabis for medical purposes, with roughly half citing mental health as their primary reason. Notably, regulatory frameworks in multiple US jurisdictions approved cannabis products for conditions like PTSD before rigorous randomized controlled trials had been conducted to test their efficacy.
Cannabis does have established therapeutic applications in other domains. Evidence supports its use in certain epilepsy presentations, MS spasticity, and select pain conditions—areas where the clinical trial evidence is more robust. However, the psychiatric indications driving the majority of medical cannabis use in the population remain either untested in controlled settings or demonstrating no significant advantage over placebo. This divergence between regulatory status and evidence-based findings underscores the urgency of conducting adequately powered RCTs for the psychiatric conditions millions of patients are currently using cannabis to treat.
What this means
Frequently asked questions
Why hasn’t depression been studied in cannabis RCTs if it’s such a common reason for use?
The review does not explain the historical reasons for this gap, but it highlights a critical void in the evidence base. Depression is one of the leading psychiatric indications for medical cannabis prescription, yet no randomized controlled trial has formally tested its efficacy. This represents an urgent priority for future research, as millions of patients are using cannabis for a condition that has never been properly evaluated against placebo.
If no effect was found for anxiety and PTSD, why are these qualifying conditions in medical cannabis programs?
According to The Lancet Psychiatry analysis, more than a dozen US states list PTSD as a qualifying condition despite the absence of rigorous RCT evidence demonstrating efficacy. The review notes that regulatory approval preceded clinical trial evidence in these cases, reflecting a policy pathway that did not require completed trials before product approval and patient access.
Are there any psychiatric uses of cannabis with proven benefit?
The review identified three areas with meaningful evidence signals: cannabis use disorder (moderate certainty), insomnia sleep time (moderate certainty), and tic severity in Tourette’s syndrome (low certainty). However, even these findings show limited or mixed evidence grades. Cannabis has stronger evidence in non-psychiatric indications such as epilepsy and MS spasticity, but for the mental health conditions driving most medical cannabis use, evidence remains minimal.
As the gap between regulatory approval and clinical evidence becomes increasingly apparent, the priority for both researchers and policymakers should be conducting adequately powered randomized controlled trials for psychiatric indications. The evidence base for cannabis in established conditions like epilepsy and MS spasticity demonstrates that rigorous trials are feasible and informative. Until comparable evidence accumulates for psychiatric disorders, clinicians and patients must navigate prescribing decisions with the understanding that efficacy for most mental health indications remains unproven. For further analysis of cannabis research across health conditions, see our coverage of latest studies and clinical updates.
Source: The Lancet Psychiatry (2025); systematic review of 54 randomized controlled trials
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Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD. Spotted an error? Contact the editorial team.
