For all participants, self-report data were available on whether the participant had ever used cannabis during their lifetime: yes (1) versus no (0). Measurement instruments and phrasing of the questions about lifetime cannabis use differed across the samples. For the ICC study this has been described for each cohort in the original paper10. As part of their online questionnaire, 23andMe used the following phrase to examine lifetime cannabis use: ‘Have you ever in your life used the following: Marijuana?’. The UK-Biobank – as part of an online follow-up questionnaire - asked: ‘Have you taken CANNABIS (marijuana, grass, hash, ganja, blow, draw, skunk, weed, spliff, dope), even if it was a long time ago?’.
