Both the TLI (OR = 1.32, p = .02, 95% CI [1.04, 1.69]) and age at the time of first alcohol use (OR = .78, p < .001, 95% CI [.68, .90]) predict AUD by age 22. Age at the time of first alcohol use mediates the association between TLI and AUD (z = 2.23, p = .03). Similarly, the TLI (OR = 1.59, p < .001, 95% CI [1.24, 2.05]) and age at the time of first cannabis consumption (OR = .85, p < .001, 95% CI [.79, .91]) predict CUD. Paralleling the results for alcohol, age at the time of first cannabis use mediates the association between TLI and CUD (z = 3.06, p = .002). These findings demonstrate that age of onset of alcohol and cannabis use presaging AUD and CUD is an indicator of transmissible risk for each disorder.
