A Critical Review of Cannabis Use and its Impact on Depression, Anxiety, and Psychotic Disorders

Abstract

Cannabis remains the most widely used controlled substance worldwide, and its relationship with common and severe mental disorders continues to generate scientific and public health debate. This narrative review synthesises evidence published across pharmacological, epidemiological, and clinical literatures examining associations between cannabis use and depression, anxiety, and psychotic disorders. Longitudinal and population-based studies converge on modest but consistent associations between regular cannabis use and incident depressive symptoms, with weaker and more heterogeneous evidence for anxiety disorders, where self-medication and reverse-causal pathways appear relevant. The strongest and most replicated signal concerns psychosis, where dose-dependent relationships with frequency of use, potency, and age of onset are well documented, and where genetic vulnerability appears to moderate risk. Cannabidiol has shown a distinct pharmacological profile from delta-9-tetrahydrocannabinol, exhibiting anxiolytic and, in early trials, antipsychotic properties, which complicates any unitary narrative about cannabis as uniformly harmful or benign. Jurisdictions that have legalised recreational cannabis show emerging, though not yet conclusive, increases in cannabis-attributable psychiatric service utilisation, particularly for psychosis and cannabis use disorder. This review discusses the pharmacological basis of these associations through the endocannabinoid system, appraises the methodological strengths and limitations of the underlying evidence base, summarises moderating factors including potency, adolescent exposure, and genetic polymorphisms, and considers implications for clinical screening, prevention, and policy. The review concludes that cannabis use constitutes a modifiable risk factor for adverse mental health outcomes that is neither trivial nor deterministic, and that risk stratification by pattern of use, age, and individual vulnerability should guide both clinical practice and public health messaging.