Although mental disorders have been shown to predict subsequent substance disorders, it is not known whether substance disorders could be cost-effectively prevented by large-scale interventions aimed at prior mental disorders. Although experimental intervention is the only way to resolve this uncertainty, a logically prior question is whether the associations of mental disorders with subsequent substance disorders are strong enough to justify mounting such an intervention. We investigated this question in this study using simulations to estimate the number of substance disorders that might be prevented under several hypothetical intervention scenarios focused on mental disorders.

Data came from the National Comorbidity Survey Replication (NCS-R), a nationally representative US household survey that retrospectively assessed lifetime history and age of onset of DSM-IV mental and substance disorders. Survival analysis using retrospective age-of-onset reports was used to estimate associations of mental disorders with subsequent substance dependence. Simulations based on the models estimated effect sizes in several hypothetical intervention scenarios.

Although successful intervention aimed at mental disorders might prevent some proportion of substance dependence, the number of cases of mental disorder that would have to be treated to prevent a single case of substance dependence is estimated to be so high that this would not be a cost-effective way to prevent substance dependence (in the range 76–177 for anxiety-mood disorders and 40–47 for externalizing disorders).

Treatment of prior mental disorders would not be a cost-effective way to prevent substance dependence. However, prevention of substance dependence might be considered an important secondary outcome of interventions for early-onset mental disorders.

The ‘gateway’ pattern of drug initiation describes a normative sequence, beginning with alcohol and tobacco use, followed by cannabis, then other illicit drugs. Previous work has suggested that ‘violations’ of this sequence may be predictors of later problems but other determinants were not considered. We have examined the role of pre-existing mental disorders and sociodemographics in explaining the predictive effects of violations using data from the US National Comorbidity Survey Replication (NCS-R).

The NCS-R is a nationally representative face-to-face household survey of 9282 English-speaking respondents aged 18 years and older that used the World Health Organization (WHO) Composite International Diagnostic Interview (CIDI) to assess DSM-IV mental and substance disorders. Drug initiation was estimated using retrospective age-of-onset reports and ‘violations’ defined as inconsistent with the normative initiation order. Predictors of violations were examined using multivariable logistic regressions. Discrete-time survival analysis was used to see whether violations predicted progression to dependence.

Gateway violations were largely unrelated to later dependence risk, with the exception of small increases in risk of alcohol and other illicit drug dependence for those who initiated use of other illicit drugs before cannabis. Early-onset internalizing disorders were predictors of gateway violations, and both internalizing and externalizing disorders increased the risks of dependence among users of all drugs.

Drug use initiation follows a strong normative pattern, deviations from which are not strongly predictive of later problems. By contrast, adolescents who have already developed mental health problems are at risk for deviations from the normative sequence of drug initiation and for the development of dependence.

Few studies have investigated non-suicidal self-injury (NSSI), or the deliberate, direct destruction of body tissue without conscious suicidal intent, and the motivations for engaging in NSSI among adolescents. This study assessed the prevalence, associated clinical characteristics, and functions of NSSI in a community sample of adolescents.

A total of 633 adolescents completed anonymous surveys. NSSI was assessed with the Functional Assessment of Self-Mutilation (FASM).

Some form of NSSI was endorsed by 46·5% (n=293) of the adolescents within the past year, most frequently biting self, cutting/carving skin, hitting self on purpose, and burning skin. Sixty per cent of these, or 28% of the overall sample, endorsed moderate/severe forms of NSSI. Self-injurers reported an average of 12·9 (s.d.=29·4) incidents in the past 12 months, with an average of 2·4 (s.d.=1·7) types of NSSI used. Moderate/severe self-injurers were more likely than minor self-injurers, who in turn were more likely than non-injurers, to have a history of psychiatric treatment, hospitalization and suicide attempt, as well as current suicide ideation. A four-factor model of NSSI functions was indicated, with self-injurers likely to endorse both reasons of automatic reinforcement and social reinforcement. The most common reasons for NSSI were ‘to try to get a reaction from someone’, ‘to get control of a situation’, and ‘to stop bad feelings’.

Community adolescents reported high rates of NSSI, engaged in to influence behaviors of others and to manage internal emotions. Intervention efforts should be tailored to reducing individual issues that contribute to NSSI and building alternative skills for positive coping, communication, stress management, and strong social support.