Table 2.

Adjusted odds ratios with their 95% confidence limits reflecting associations between tobacco, alcohol, and cannabis use and misuse and liability to ADHD and autistic traits in 3,080 Australian twins, ages 27–40 years, after sex, age, zygosity (identical vs. fraternal), and a lifetime history of conduct disorder were controlled for

Variable	ADHD symptoms		Autistic traits
	1–2	≥3	1–2	3–5	≥6
Smoking
Ever smoked tobacco	1.11 [0.83, 1.47]	1.09 [0.80, 1.48]	0.94 [0.71, 1.26]	0.86 [0.63, 1.18]	1.02 [0.72, 1.44]
Regular tobacco smoking	1.17 [0.97, 1.41]	1.24*b [1.00, 1.54]	1.21 [0.98, 1.50]	1.46**ab [1.16, 1.84]	1.79**a [1.40, 2.28]
DSM-IV nicotine dependence	1.20 [0.96, 1.49]	1.52**b [1.22, 1.90]	1.25 [0.96, 1.62]	1.84**ab [1.40, 2.43]	2.30**a [1.74, 3.06]
DSM-IV nicotine dependence (conditional on regular use, n = 1,273)	1.10 [0.82, 1.47]	1.62**a [1.19, 2.21]	1.13 [0.80, 1.60]	1.74**a [1.20, 2.51]	2.07**a [1.42, 3.00]
Alcohol
Monthly drinking	1.23 [0.87, 1.74]	0.98 [0.68, 1.39]	0.98 [0.68, 1.42]	0.75 [0.51, 1.10]	0.76 [0.50, 1.15]
Drinking to intoxication	1.36 [0.99, 1.84]	1.02 [0.75, 1.38]	0.99 [0.72, 1.36]	0.70* [0.50, 0.97]	0.71 [0.49, 1.03]
DSM-IV alcohol dependence	1.50**a [1.21, 1.86]	1.91**a [1.52, 2.39]	1.06 [0.82, 1.38]	1.23 [0.94, 1.61]	1.42*a [1.07, 1.87]
DSM-IV alcohol dependence (conditional on monthly use, n = 2,809)	1.50**a [1.20, 1.86]	1.96**a [1.55, 2.46]	1.07 [0.82, 1.39]	1.28 [0.98, 1.68]	1.47**a [1.11, 1.95]
Cannabis
Ever used cannabis	1.34** [1.09, 1.64]	1.17 [0.93, 1.47]	1.10 [0.89, 1.36]	1.06 [0.84, 1.35]	1.15 [0.89, 1.49]
Used cannabis ≥11 times	1.31*ab [1.06, 1.61]	1.09 [0.87, 1.37]	1.35*a [1.07, 1.70]	1.36*a [1.06, 1.75]	1.75**b [1.35, 2.28]
DSM-IV cannabis abuse/dependence	1.24 [0.95, 1.62]	1.41*ab [1.07, 1.85]	1.32 [0.96, 1.81]	1.46*a [1.05, 2.04]	2.02**b [1.44, 2.85]
DSM-IV cannabis abuse/dependence (conditional on repeated use, n = 946)	1.07 [0.77, 1.49]	1.68** [1.16, 2.43]	1.03 [0.68, 1.57]	1.21 [0.79, 1.85]	1.50 [0.96, 2.33]

Notes: ADHD = attention-deficit/hyperactivity disorder; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition.

^abOdds ratios with identical superscripts could be statistically equated to each other at p > .05.

^*Indicates significant at p < .05;

^**indicates significant at p < .008, which refers to the Bonferroni correction for two phenotypes (ADHD vs. autistic traits) and three substances (alcohol, nicotine, and cannabis), that is, .05 / 6 = .0083.