Youth in transition: Study protocol of a prospective cohort study into the long-term course of addiction, mental health problems and social functioning in youth entering addiction treatment

Substance use disorders (SUDs) are prevalent in the general adult population [1], tend to follow a chronic or chronic-intermittent course, are associated with many individual and social problems, and – as most mental disorders – often have their onset in adolescence [2]. Hence, the course of SUD among adolescents and young adults should be high on our research agenda. Nevertheless, the literature regarding the development, persistence or desistance and treatment of SUD in youth is sparse, and research in this area lags considerably behind that of research in adult SUD.

When studying substance use ‘trajectories’ several transitions can be distinguished. The first series of transitions cover the initiation of substance use, and the transition from first use to regular or frequent use, and from frequent use to disordered use. The subsequent transition pertains to the persistence or desistance of SUD. In the present study we examine the last transition – the persistence of or desistance from SUD in the period from late adolescence (i.e., 16 to 22 yrs) to early adulthood (20 to 26 yrs) – among youth in addiction treatment.

Various prospective studies have traced the progression from first substance use through frequent consumption to the onset of SUD in community samples of adolescents, with most studies pertaining to cannabis, the most commonly used illicit drug worldwide [3‐7]. Most substance use in adolescents remains experimental, irregular or modest. However, it tends to become more frequent, intensive and long-lasting when the use of substances is part of multiple problem behavior including comorbidity with mental health problems, social dysfunction, and delinquency [7‐9].

Much less is known about what happens next: the course of SUD during the critical transition period from adolescence to adulthood. Based on Moffitt’s taxonomy of antisocial behavior [10, 11], the literature distinguishes between adolescent-limited and life-course-persistent trajectories of substance use and SUD, but few prospective population studies have in fact addressed this issue, and virtually all studies were conducted in the United States, Australia and New Zealand [12‐16]. For example, Meier et al. (2015) investigated the development of persistent substance dependence on alcohol, nicotine, cannabis or hard drugs from adolescence to adulthood up to 38 years in the Dunedin birth cohort in New Zealand, and found a persistence rate of substance dependence of 19% when including nicotine dependence, and of 9% when excluding nicotine dependence from the outcome. In addition, they found a specific set of childhood and adolescent risk factors, including family history of SUD, childhood psychopathology, and childhood socioeconomic status, to be strongly associated with persistent substance dependence in adulthood. Only a few European population studies investigated the course of SUD from adolescence to young adulthood, but these focused on cannabis only [17, 18].

The present study focuses on a population that is particularly at risk for chronicity: adolescents in addiction treatment. Although research on treatment outcome of adolescents with SUD has expanded in the past decade [19], there are remarkably few studies that investigated the course of SUD in adolescents following addiction treatment prospectively for longer than 1 year. We found only three large-scale (N > 300) studies that did so [20‐22]. Results from these – all US-based – studies suggest that, despite overall treatment benefit, roughly 15 to 30% of treated adolescents show a pattern of persistent SUD/dependence or even deterioration during the 3 to 6 years post-treatment.

To conclude, the available data from prospective population surveys and treatment-outcome studies on the course of SUD in adolescents are limited at best. Remission, continuation and progression rates are largely unknown, as are the risk and protective factors involved. While nearly 6000 youth aged 22 years or younger enter treatment for SUD annually in the Netherlands [23], we have virtually no information as to how these youth will fare moving from adolescence to early adulthood. The present study aims to fill these gaps by addressing the study objectives outlined below.

In this study, we will investigate the rate of persistent SUD and its predictors longitudinally from adolescence to young adulthood in a representative treatment sample of youth with DSM-5 SUD from the start of their addiction treatment to 2 and 4 years following treatment-entry. In addition to SUD, we will investigate the course of comorbid mental disorders and social functioning, and their relation with SUD over time.

Our primary study questions are:

This study aims to investigate the long-term course of SUD, concurrent mental health problems and social functioning in a group that is particularly at risk for chronicity: youth in addiction treatment. Strengths of the study are (1) obtaining a nationally representative sample of youth in addiction treatment, (2) the relatively large size of our cohort, (3) the use of both self-report and endophenotypical biological and cognitive-behavioral data, and (4) our aim to determine the long-term outcome of youth addiction treatment in a naturalistic, ‘real world’ treatment context. Study limitations include the following. First, our study sample consists of youth aged 16 to 22 years. We would have preferred to include younger adolescents as well, but Dutch national registration data showed that only 618 youths aged 15 years and younger seek help at addiction treatment annually (i.e., 11% of total youths’ treatment demand). Second, our maximum follow-up period is 4 years. We would have preferred a longer follow-up period (e.g., 8 to 10 years) to sufficiently cover the age of young adulthood, but this was not possible due to budget limitations. Third, our study data are in essence correlational in nature, and hence, are subject to confounding. Including a non-treatment control group would limit confounding, but for reasons of feasibility, ethics and costs, we chose not to include a non-treatment (matched) control cohort in our study. Another option would have been to conduct a large-scale randomized controlled trial (RCT), but for obvious reasons an RCT with a non-treatment control group would be unacceptable for ethical reasons. Nevertheless, we will include important and well-known confounders like social economic status in our analyses. Lastly, most of our data are based on self-report and may be subject to underreporting. Self-reported substance use can be verified by means of urinalyses, but this method only provides a momentary assessment and does not give an indication of amount or severity of use. Studies indicate that self-report is quite reliable if confidentiality is guaranteed and if no negative consequences are attached to the answers provided by the person [61, 62]. To assure that this will be the case, our study assessments will be conducted by research-assistants that are independent from treatment-staff. Nevertheless, youths with insufficient comprehension of basic Dutch language will be barred from the study (exclusion criterion), and hence this potentially important subpopulation will not be represented in our study data.

All in all, we are confident that this study will further our understanding of (1) the course of SUD in youths seeking help for their addiction problems, (2) the relationship between SUD and comorbid mental disorders and social functioning over time, and (3) the determinants and consequences of persistent SUD during the transition from adolescence to young adulthood.