OPN1MW and cannabis dependence: Cannabis dependence (SDS) was positively correlated with THC-COOH/creatinine in urine (rpb(345) = 0.350, p ⩽ 0.001), THC in hair (rφ(412) = 0.206, p ⩽ 0.001), CBD in hair (rφ(412) = 0.178, p ⩽ 0.001), CBN in hair (rφ(412) = 0.215, p ⩽ 0.001) THC-COOH in hair (rφ(412) = 0.170, p ⩽ 0.001), THC-OH in hair (rφ(412) = 0.135, p = 0.006), days per month of cannabis use (rpb(398) = 0.486, p ⩽ 0.001), preference for high potency cannabis (rφ(412) = 0.212, p ⩽ 0.001) and the amount of money spent on cannabis per week (rpb(411) = 0.412, p ⩽ 0.001).