Cannabis and Mental Health: A Systematic Review and Meta-analysis of the Neuropsychiatric Effects, Therapeutic Potentials, and Policy Implications of THC and CBD

Abstract

Aim: This systematic review and meta-analysis examined the neuropsychiatric effects of cannabis, focusing on the contrasting roles of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). It evaluated their associations with psychiatric outcomes, assessed the therapeutic potential of cannabis-based products (CBPs), and identified evidence gaps relevant to clinical practice and mental health policy.Methods: The review was conducted in accordance with PRISMA guidelines. Electronic databases (PubMed, Scopus, Web of Science, Cochrane Library, and Google Scholar) were searched for studies published between 2005 and 2025. Eligible studies included randomized controlled trials, observational studies, mixed-methods studies, and systematic reviews investigating the psychiatric or neuropsychological effects of THC, CBD, or CBPs. Study quality was assessed using the Joanna Briggs Institute critical appraisal tools. Meta-analysis was performed where appropriate, and narrative synthesis was used for heterogeneous outcomes.Results: Of 3,503 records identified, 14 studies met the inclusion criteria. THC was consistently associated with an increased risk of psychotic symptoms, cognitive impairment, and anxiety, whereas CBD demonstrated potential antipsychotic, anxiolytic, and neuroprotective effects. Evidence for CBPs in treating psychiatric disorders was limited, with modest short-term benefits but insufficient support for long-term efficacy. Small sample sizes, heterogeneous dosing regimens, and inconsistent outcome measures limited the strength of the evidence.Conclusion: THC and CBD exhibit distinct neuropsychiatric profiles. Although CBD shows therapeutic promise, robust evidence supporting its long-term effectiveness in psychiatric care remains insufficient. Standardized clinical trials are needed to establish optimal dosing, evaluate long-term safety and efficacy, and inform evidence-based clinical guidelines and public health policies.