Developmental epidemiology of drug use and abuse in adolescence and young adulthood: Evidence of generalized risk

Abstract

Past studies highlight a narrowing gender gap and the existence of a shared etiology across substances of abuse; however, few have tested developmental models using longitudinal data. We present data on developmental trends of alcohol, tobacco, and marijuana use, abuse and dependence assessed during adolescence and young adulthood in a community-based Colorado twin sample of 1733 respondents through self-report questionnaires and structured psychiatric interviews. Additionally, we report on the rates of multiple substance use and disorders at each developmental stage, and the likelihood of a substance use disorder (SUD; i.e., abuse or dependence) diagnosis in young adulthood based on adolescent drug involvement. Most notably, we evaluate whether the pattern of multiple substance use and disorders and likelihood ratios across substances support a model of generalized risk. Lastly, we evaluate whether the ranked magnitudes of substance-specific risk match the addiction liability ranking. Substance use and SUDs are developmental phenomena, which increase from adolescence to young adulthood with few and inconsistent gender differences. Adolescents and young adults are not specialized users, but rather tend to use or abuse multiple substances increasingly with age. Risk analyses indicated that progression toward a SUD for any substance was increased with prior involvement with any of the three substances during adolescence. Despite the high prevalence of alcohol use, tobacco posed the greatest substance-specific risk for developing subsequent problems. Our data also confirm either a generalized risk or correlated risk factors for early onset substance use and subsequent development of SUDs.

Introduction

Epidemiologic studies have demonstrated that the prevalence of drug use and abuse increases with age during adolescence and peaks in young adulthood (Johnston et al., 2008; SAMHSA, 2006, SAMHSA, 2008). Substance experimentation is common in adolescence and substantially elevates the risk for persistent substance use, substance use disorders (SUDs; i.e., abuse/dependence) and other comorbid disorders in later life stages (Bauman and Phongsavan, 1999, Brook et al., 1999, Gould et al., 1977, Kapusta et al., 2007, Riggs et al., 2007, Winters and Lee, 2008). Additionally, involvement with multiple substances and the risk for substance use problems appear to be driven by either a common risk factor or correlated risk factors (Grant and Dawson, 1998, Gil et al., 2004, Grant et al., 2006, Kendler et al., 2007, Kendler et al., 2008, Rhee et al., 2003, Rhee et al., 2006, Young et al., 2006). Despite this wealth of information, our understanding of substance use and related problems in youth remains limited by the fact that most data are cross-sectional. This permits investigation of cohort differences or temporal change, but does not allow for developmental models to be explicitly tested.

This study extends our previous work on adolescent substance use patterns among community adolescents in Colorado (Young et al., 2002) who have now been followed longitudinally into young adulthood, by addressing two primary questions that remain largely unanswered. First, are there gender differences in the developmental trends in substance use, abuse, and dependence? Second, is there epidemiological evidence to support a model of generalized risk across alcohol, tobacco, and marijuana use and disorders?

Although gender differences in alcohol use in adolescence are typically modest (Hicks et al., 2007, Johnston et al., 2008, Young et al., 2002), adult studies consistently show higher levels of alcohol consumption and a greater prevalence of alcohol use disorders among men (Prescott, 2001, Prescott, 2003, SAMHSA, 2008, Sher et al., 2005). However, recent reports show that the gender gap in drinking behavior has narrowed in recent decades (Holdcraft and Iacono, 2002, Keyes et al., 2008, Rice et al., 2003), which may be attributed, in part, to changes in cultural attitudes toward drinking (Holmila and Raitasalo, 2005). Based on large epidemiologic surveys such as the Monitoring the Future Survey (MTF; Johnston et al., 2008), we would expect only modest gender differences in cigarette and marijuana smoking in adolescence. Their data on young adults show that while rates of marijuana use are higher among males in this age range, gender differences in rates of cigarette smoking remain small. Although these cross-sectional data do not address developmental issues, they are consistent with one of the few longitudinal studies of substance use in adolescence and young adulthood, which also shows that substance related problems in males escalate in young adulthood at a greater rate than in females (Hicks et al., 2007). Based on these data, we anticipated only modest gender differences in our Wave 1 adolescent data, and that these differences would expand in our Wave 2 young adult data, particularly for alcohol and marijuana.

The substance abuse literature documents an ongoing interest in understanding the risk factors underlying substance use and related disorders. While substance-specific factors have been supported, the high rates of comorbidity among nicotine, alcohol, and illicit substances have led many researchers to concentrate on risk factors that may be common across multiple substances. For example, Rhee and colleagues (2003) utilized simulated family data to discriminate between 13 different models of comorbidity defined by Neale and Kendler (1995), and then applied this methodology in a clinically ascertained adolescent sample (Rhee et al., 2006). Results suggested that two models were equally likely to explain the patterns of comorbidity observed. The first model, referred to as the correlated liability model, hypothesizes that each substance has its own set of risk factors (i.e., liability) and that these factors are correlated, accounting for poly-substance use and comorbid SUDs. The second plausible model, the alternate forms model, hypothesizes that comorbidity is driven by a single risk factor which manifests itself as an array of deviant behaviors, including substance use and SUDs. Both models are consistent with observed prevalence rates of comorbidity that exceed those predicted from the rates of use, abuse, and dependence on individual substances when assuming independent liabilities. In the current study we examine the patterns of single and multiple drug involvement in both adolescence and young adulthood while making comparisons to expected rates based on a model of independent liabilities. By comparing the expected and observed rates of multiple substance use and SUDs we are able to test if these liabilities are independent. We hypothesized that the patterns of multiple substance use and abuse in adolescence and young adulthood would support a model of generalized risk. Additionally, given that young adulthood is a period during which drug initiation and progression to problematic use remains frequent (Wagner and Anthony, 2002), we also hypothesized that the prevalence of lifetime multiple substance use and abuse would increase from adolescence to young adulthood.

Data from prospective longitudinal studies have consistently shown that the onset of substance use in adolescence confers a particularly potent risk for persistent use and the development of substance use disorders (Bonomo et al., 2004, Brook et al., 1999, Duncan et al., 1997, Gil et al., 2004, Lewinsohn et al., 1999, McGue and Iacono, 2008, Timberlake et al., 2007). These data can provide another mechanism for examining possible generalized risk factors by comparing the probability of developing a SUD on substance A, given adolescent use of substance A versus adolescent use of substance B. For example, does smoking in adolescence primarily predict tobacco/nicotine dependence in young adulthood and only minimally predict problems with other substances (evidence of specific risk)? Alternatively, is adolescent smoking as predictive of later marijuana abuse or dependence as it is predictive of later nicotine dependence (evidence of generalized risk)? Using longitudinal data collected in adolescence and young adulthood, we asked whether the likelihood of developing an alcohol, tobacco, or marijuana SUD during young adulthood depends on adolescent drug involvement with a particular substance or any substance.

With our third analytical approach we investigated whether onset of use in adolescence predicts the development of a SUD in young adulthood to the same degree for tobacco, alcohol, and marijuana. Goldstein and Kalant (1990) rank ordered the relative risk of addiction of several drug categories by the “addictiveness” of each drug based on animal studies examining self-administration of substances, engagement in drug seeking behavior, and latency to relapse after enforced abstinence. The addiction liability ranking suggested that tobacco was the most addictive of the three substances, followed by alcohol, and lastly marijuana (Goldman et al., 2005, Goldstein and Kalant, 1990). Based on these findings we predicted that the magnitude of risk for a SUD in young adulthood, given adolescent onset of use, would be consistent with the addiction liability ranking. If supported, this pattern would suggest that in addition to generalized risk factors, there are also important substance-specific mechanisms that increase the risk for developing SUDs.