At W5, adolescents were on average 16.7 years old (SD=1.3, range 12–19 years). presents distributions of covariates; rates of ND and psychiatric disorders. Rates of dependence were similar by gender. Anxiety, mood disorder, and ODD rates were higher among females than males. Disorders were comorbid, especially anxiety and mood (OR=5.7, CI=3.7–8.8). Comorbidity of disruptive with anxiety and mood disorder was lower (ORs=2.9, CI’s=1.9–4.3, 2.0–4.2). More new cases of ND than psychiatric disorders occurred after baseline. By W5, rates increased by 48% for one ND criterion, 60% for full dependence, 39.0% for anxiety, 27.5% for disruptive, and 20.2% for mood disorders.
Prevalence and means of adolescent covariates by wave 5 and of parental self-reported covariates by wave 1 among lifetime smokers (n=814)
Rates of adolescent lifetime psychiatric disorders and nicotine dependence at baseline and by wave 5 by gender (lifetime smokers by wave 5, n=814)
Different patterns of association with ND levels were observed across psychiatric disorders (). For anxiety disorder, youths with full ND had at least twice the risk as those with 1–2 or zero criteria. For mood disorder, risk among dependent youths did not vary with number of positive symptoms but was twice that of asymptomatic youths. For disruptive disorder, risk increased at each successive dependence level. Youths reporting 3 or more criteria were over twice as likely as those reporting 1–2 criteria and 15 times as likely as those without criteria to be diagnosed with all three psychiatric disorder classes.
Rates of lifetime psychiatric disorders by level of nicotine dependence among lifetime smokers by wave 5 (n=814)
Temporal ordering of psychiatric disorders and nicotine dependence
On average, psychiatric disorders began at a younger age than tobacco use (1.3–2.4 years lower) and first ND criterion (2.5–3.7 years lower). Mean onset ages were: anxiety 10.7 years (SD=4.0, N=100), mood 11.7 (SD=2.9, N=149), disruptive behavior 10.6 (SD=3.3, N=244), tobacco use 13.0 years (SD=2.1, N=814), first dependence criterion 14.3 years (SD=1.6, N=429), third criterion 14.7 years (SD=1.5, N=207). Three groups were defined for each ND outcome (first criterion, full ND): onset of psychiatric disorder before, after, and same age as dependence. For disruptive disorder, 80.6%, preceded the first criterion, 14.3% followed, 5.1% were tied; the percentages were 86.4%, 9.2%, 4.4%, respectively, for full dependence. For mood disorder the percentages were 76.6%, 12.8%, 10.6% for first criterion; 82.8%, 11.0%, 6.2% for full dependence. For anxiety disorder the percentages were 70.0%, 17.0%, 13.0% for first criterion; 79.4%, 7.3%, 13.3% for full dependence.
Psychiatric disorders as predictors of nicotine dependence
Cox proportional hazards models estimated the risk from psychiatric disorders for onset of first criterion and full ND among smokers. At the univariate level, except for anxiety disorder, each psychiatric disorder class predicted onset of the first criterion; all three psychiatric disorder classes predicted full dependence (). Controlling for comorbidity among disorders and other covariates, only disruptive disorder predicted onset of the first dependence criterion; disruptive and anxiety disorder predicted full dependence. Mood disorder no longer predicted dependence. Disruptive disorder and initial pleasant sensitivity accounted for the effect of mood on the first criterion; disruptive disorder did for full dependence.
Additional statistically significant common predictors of first criterion and full dependence included earlier onset age of tobacco use, initial pleasant tobacco experiences, alcohol or illicit drug use, particularly abuse or dependence. Parental ND predicted full ND. Initial negative tobacco experiences and parental depression reduced onset of first dependence criterion. Males with a delinquent parent, and white and Hispanic females were more likely to develop a dependence criterion.
Specific psychiatric disorders as predictors of nicotine dependence
Models were re-estimated disaggregating the broad classes of psychiatric disorders into nine specific disorders. For onset of first ND criterion, MDD (HR=1.5, CI=1.2–2.0), ADHD (HR=2.5, CI=1.5–4.2), ODD (HR=2.3, CI=1.7–3.0), and CD (HR=1.6, CI=1.3–2.1) were statistically significant univariate predictors. Controlling for covariates, only ADHD (HR=2.4, CI=1.4–4.0) and ODD (HR=1.6, CI=1.2–2.2) remained significant. For onset of full dependence, the same diagnoses as for the first criterion, MDD (HR=1.7, CI=1.2–2.3), ADHD (HR=2.5, CI=1.3–4.7), ODD (HR=2.4, CI=1.6–3.4), CD (HR=2.0, CI=1.5–2.8), plus panic disorder (HR=2.9, CI=1.7–4.9), were statistically significant univariate predictors. Controlling for covariates, only panic disorder predicted full dependence (HR=2.2, CI=1.2–3.9).
Nicotine dependence as predictor of psychiatric disorders
Two sets of Cox proportional hazards models estimated influence of time-varying ND (first criterion, full dependence) on onsets of anxiety, mood, or disruptive behavior disorders. First, tobacco users at the time they experienced their first ND criterion were compared with users without ND criteria. Second, tobacco users at the time they experienced three ND criteria were compared with users with 0–2 criteria. Coefficients for periods prior to tobacco use are not shown.
Since multivariate results for both outcomes are similar, presents models for full ND. With control for other covariates, ND, whether first criterion or full syndrome, predicted only disruptive disorder. Psychiatric disorders were strong and consistent predictors of each other’s onset. Abuse or dependence on illicit drugs was the strongest predictor of anxiety disorder. Parental depression predicted youth mood disorder; parental delinquency predicted youth mood and disruptive disorders. Females were more likely than males to develop an anxiety or mood disorder; African-Americans were less likely than whites to develop a mood disorder but more likely to develop a disruptive disorder.
Nicotine dependence as predictor of specific psychiatric disorders
Models predicting onset of specific psychiatric disorders within a class were estimated (except ADHD). At the univariate level, the first criterion and full dependence predicted onsets of ODD (HRs=2.1, CI=1.1–4.0 and 3.0, CI=1.3–7.0, respectively) and CD (HR=2.3, CI=1.2–4.3, HR=3.1, CI=1.3–7.3). Full dependence also predicted onset of panic attacks without disorder (HR=4.0, CI=1.0–15.9). Controlling for covariates, including specific psychiatric disorders other than the one being predicted, the first criterion and full ND predicted ODD onset (HR=2.0, CI=1.0–4.0 and HR=3.7, CI=1.4–9.5)