Psychiatric Genomics Consortium cases met criteria for a lifetime diagnosis of DSM-IV (or DSM-III-R) cannabis abuse or dependence11 derived from clinician ratings or semi-structured interviews.7 Cases from the iPSYCH sample had ICD-10 codes of F12.1 (cannabis abuse) or F12.2 (cannabis dependence), or both in the Danish Psychiatric Central Research Register;12 the remaining individuals in the sample were used as controls. Cases in the deCODE sample met criteria for lifetime DSM-III-R or DSM-IV cannabis abuse or dependence or DSM-5 cannabis use disorder according to diagnoses made at the National Center of Addiction Medicine in Iceland, whereas controls were derived from the general population of Iceland (appendix pp 2–3). Exposure data were not available for some large groups (eg, iPSYCH and deCODE); therefore, controls were defined regardless of lifetime cannabis exposure across all datasets.
