Violations of the usual sequence of drug initiation: prevalence and associations with the development of dependence in the New Zealand Mental Health Survey.

Objective: For 3 decades, studies have reported that the usual sequence of drug initiation is licit drugs, then cannabis, and then other illicit drugs. This article describes the prevalence of violations of this sequence, the predictors of violations, and the relationship between violations and the onset of alcohol or drug dependence.

Method: The New Zealand Mental Health Survey is a nationally representative sample with 12,992 face-to-face interviews carried out in 2003-2004. The response rate was 73.3%. The World Health Organization Composite International Diagnostic Interview (CIDI 3.0) was used in the survey. Reports of the age at first use were obtained for alcohol and drugs but not for smoking.

Results: Violations of the usual sequence of drug initiation were uncommon in the population (2.6%). Use of other illicit drugs before cannabis was the main violation, found in 2.3% of alcohol users, 3.0% of cannabis users, 8.6% of cocaine users, and 16.7% of those who had used other illicit drugs. Use of other illicit drugs before cannabis was more predominant in younger cohorts and those with more early-onset internalizing disorders. Violations had little association with the development of dependence in users when other important predictors such as age at onset of use and the number of illicit drugs used were taken into account. Internalizing disorders and early-onset bipolar disorder also predicted dependence.

Conclusions: In New Zealand, violations of the gateway sequence are not common and they are not markers of progression to dependence.