Cannabis-Related Neuropsychiatric and Developmental Harm: Evidence, Original Meta-Analyses, and a Questionnaire for Estimating Risk

Background and objectives: Cannabis-related harms vary across psychiatric, cognitive, neurological, developmental and functional outcomes. This monograph combines a critical evidence review with original secondary meta-analyses and probability modeling to assess harm, susceptibility and recovery, and to develop a literature-derived risk questionnaire.Methods: Original frequentist and Bayesian random-effects meta-analyses of published longitudinal estimates were conducted under six selected specifications for psychosis, depression and anxiety, with source-verification, cohort-overlap and prior-sensitivity analyses. Published reviews, cohorts and experiments were critically synthesized. Eight MEDLINE-source queries with a publication cutoff of 18 October 2026 yielded 1,719 title assessments and 292 documented abstract assessments. Twenty-five principal regression specifications and two alternative cannabis use disorder models were fitted to published longitudinal aggregates to support a forty-five-item questionnaire. Cannabis use disorder models underwent internal held-out comparisons and 500 bootstrap replications. Prenatal associations underwent dependence and numerical-precision analyses.Results: The original two-cohort synthesis of higher adolescent exposure and psychotic disorder yielded a pooled relative association of 2.67 (modified Hartung–Knapp 95% CI 0.06–115.26); the Bayesian pooled median was 2.38 (95% credible interval 1.05–4.80). All six selected frequentist intervals included unity, and strict primary-source verification left insufficient studies for an anxiety pool. Across the broader literature, evidence was strongest for acute psychiatric and cognitive effects, cannabis use disorder and withdrawal, and psychosis-related harm. Published pooled cannabis use disorder prevalence among users was 22% (95% CI 18–26%); educational disruption included increased school dropout (odds ratio 2.19; 95% CI 1.73–2.78). Cognitive differences were small on average and smaller in studies requiring abstinence. Depression, suicidality and mania showed adverse observational associations; anxiety, motivation, employment, interpersonal and neurological findings were less consistent. Prenatal associations were most consistent for impaired fetal growth and prematurity; malformation and later developmental findings were heterogeneous. Internal predictive performance varied substantially by subgroup, and modeled uncertainty frequently prevented stable risk-category assignment.Interpretation: Original meta-analyses and probability models quantify selected associations and their uncertainty within a broader assessment of cannabis-related harm. Frequent high-THC exposure, early initiation, established psychiatric illness and pregnancy warrant particular concern; causal certainty varies by outcome. Questionnaire reports provide outcome-specific source projections with uncertainty estimates. External clinical and psychometric validation has not been performed.