In a nationwide Danish study, 15% of schizophrenia cases in males and potentially one-fifth in young males could be attributed to cannabis use disorder, compared to only 4% in females.
Psychiatrists, public health policymakers, cannabis regulators, and families of young males using cannabis.
15% of male schizophreniacases in 2021 potentially attributable to cannabis use disorder in nationwide Danish register study
What the researchers found
The association between CUD and schizophrenia was significantly stronger in young males aged 16-20 (aIRR=3.84) compared to females of the same age (aIRR=1.81). By 2021, the population attributable risk fraction was 15% for males versus 4% for females.
Why it matters
This landmark study quantifies the sex difference in cannabis-schizophrenia risk and suggests that preventing CUD in young males could substantially reduce schizophrenia incidence.
The numbers in context
6.9 million individuals, 45,327 schizophrenia cases, 1972-2021. Males aHR=2.42, females aHR=2.02. Young males (16-20) aIRR=3.84. 2021 PARF: males 15%, females ~4%. Annual average PARF change: males 4.8%, females 4.0%.
How the study worked
Nationwide Danish register-based cohort study of all individuals aged 16-49 during 1972-2021, with hazard ratios, incidence risk ratios, population attributable risk fractions, and joinpoint analyses.
Who was studied
6.9 million individuals aged 16-49 in Denmark during 1972-2021, with 45,327 incident schizophrenia cases.
What this study cannot tell us
Register-based CUD diagnosis may underestimate true prevalence. Cannot prove causation despite temporal sequence. Danish population may not generalize to all countries. Changing diagnostic practices over 50 years.
How to read the evidence
Large nationwide register-based cohort with 50-year follow-up; strongest observational evidence available but cannot prove causation.
When this study was published
Covers 50 years of Danish national register data (1972-2021).
The bigger picture
This study provides the strongest population-level evidence yet that cannabis use disorder is a modifiable risk factor for schizophrenia, particularly in young males, with direct implications for prevention policy.
Replication
Landmark study; findings consistent with prior research but sex-stratified analysis is novel.
Funding
Not specified in abstract
Conflicts of interest
Not specified in abstract
Questions still open
- What biological mechanisms make young males more susceptible?
- Would preventing CUD in young males actually reduce schizophrenia incidence, or would other risk factors fill the gap?
Read the original research
Association between cannabis use disorder and schizophrenia stronger in young males than in females.
Psychological medicine, 53(15), 7322-7328
Citation
Hjorthøj, Carsten; Compton, Wilson; Starzer, Marie; Nordholm, Dorte; Einstein, Emily; Erlangsen, Annette; Nordentoft, Merete; Volkow, Nora D; Han, Beth. (2023). Association between cannabis use disorder and schizophrenia stronger in young males than in females.. Psychological medicine, 53(15), 7322-7328. https://doi.org/10.1017/S0033291723000880