Table 1.
Frequency of tobacco-smoking, alcohol, and cannabis involvement as a function of ADHD symptoms and autistic traits scores in 3,080 Australian twins, ages 27–40 years
| Variable | Full sample (N = 3,080) | ADHD symptoms |
Autistic traits |
|||||
| 0 | 1–2 | ≥3 | 0 | 1–2 | 3–5 | ≥6 | ||
| Smoking | ||||||||
| Ever smoked tobacco | 86.4 | 85.5 | 87.3 | 88.4 | 86.5 | 86.1 | 85.4 | 87.9 |
| Regular tobacco smoking | 41.5 | 36.9 | 44.9 | 51.1 | 32.8 | 38.4 | 44.1 | 51.2 |
| DSM-IV nicotine dependence | 25.0 | 20.2 | 27.1 | 37.1 | 16.0 | 20.2 | 28.5 | 36.2 |
| DSM-IV nicotine dependence (conditional on regular use, n = 1,273) | 60.3 | 54.8 | 60.3 | 72.6 | 48.8 | 52.8 | 64.7 | 70.7 |
| Alcohol | ||||||||
| Monthly drinking | 91.1 | 90.8 | 92.5 | 91.0 | 91.7 | 91.9 | 90.1 | 90.5 |
| Drinking to intoxication | 87.7 | 87.0 | 90.1 | 87.7 | 88.6 | 89.1 | 85.9 | 86.8 |
| DSM-IV alcohol dependence | 24.3 | 18.4 | 29.0 | 37.1 | 18.3 | 21.2 | 26.0 | 32.1 |
| DSM-IV alcohol dependence (conditional on monthly use, n = 2,809) | 26.7 | 20.1 | 31.3 | 40.8 | 19.8 | 23.0 | 28.8 | 35.3 |
| Cannabis | ||||||||
| Ever used cannabis | 68.4 | 65.0 | 73.4 | 73.0 | 64.6 | 68.1 | 68.7 | 71.9 |
| Used cannabis ≥ 11 times | 30.8 | 26.5 | 36.5 | 37.6 | 22.5 | 29.6 | 31.5 | 39.1 |
| DSM-IV cannabis abuse/dependence | 16.2 | 12.3 | 18.9 | 25.0 | 10.0 | 14.1 | 16.9 | 24.2 |
| DSM-IV cannabis abuse/dependence (conditional on repeated use, n = 946) | 52.7 | 46.4 | 52.0 | 66.4 | 44.5 | 47.3 | 53.6 | 61.9 |
Notes: ADHD = attention-deficit/hyperactivity disorder; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition.