Childhood socio-economic status, school failure and drug abuse: a Swedish national cohort study Karl Gauffin 1,2 , Bo Vinnerljung 3,4 , Mats Fridell 5,6 , Morten Hesse 7 & Anders Hjern 1,8 Centre for Health Equity Studies (CHESS), Karolinska Institutet/Stockholm University, Stockholm, Sweden, 1 Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden, 2 Department of Social Work, Stockholm University, Stockholm, Sweden, 3 National Board of Health and Welfare, Stockholm, Sweden, 4 Department of Psychology, Lund University, Lund, Sweden, 5 Clinical Psychology, Linnaeus University, Växjö, Sweden, 6 Centre for Alcohol and Drug Research, Aarhus University, Copenhagen S, Denmark 7 and Clinical Epidemiology/Department of Medicine, Karolinska Institutet, Stockholm, Sweden 8 ABSTRACT Aim To investigate whether socio-economic status (SES) in childhood and school failure at 15 years of age predict illicit drug abuse in youth and young adulthood. Design, setting and participants Register study in a Swedish national cohort born 1973–88 (n = 1 405 763), followed from age 16 to 20–35 years. Cox regression analyses were used to calculate hazard ratios (HR) for any indication of drug abuse. Measurements Our outcomes were hospital admissions, death and criminality associated with illicit drug abuse. Data on socio-demographics, school grades and parental psychosocial problems were collected from censuses (1985 and 1990) and national registers. School failure was defined as having mean school grades from the final year in primary school lower than -1 standard deviation and/or no grades in core subjects. Findings School failure was a strong predictor of illicit drug abuse with an HR of 5.87 (95% CI: 5.76–5.99) after adjustment for age and sex. Childhood SES was associated with illicit drug abuse later in life in a stepwise manner. The lowest stratum had a HR of 2.28 (95% CI: 2.20–2.37) compared with the highest stratum as the reference, when adjusted for other socio-demographic variables. In the fully adjusted model, the effect of SES was greatly attenuated to an HR of 1.23 (95% CI: 1.19–1.28) in the lowest SES category, while the effect of school failure remained high with an HR of 4.22 (95% CI: 4.13–4.31). Conclusions School failure and childhood socio-economic status predict illicit drug abuse independently in youth and young adults in Sweden. Keywords Childhood, cohort study, drug abuse, school failure, social inequity, socio-economic status, Sweden. Correspondence to: Karl Gauffin, Centre for Health Equity Studies (CHESS), Stockholm University/Karolinska Institutet, 10691 Stockholm, Sweden. E-mail: karl.gauffin@chess.su.se Submitted 25 June 2012; initial review completed 3 September 2012; final version accepted 21 February 2013 INTRODUCTION The importance of early life predictors for adult drug abuse has been acknowledged and addressed by a signifi- cant body of research. Genetic factors [1], developmental disorders [2], parental substance abuse and adverse childhood experiences, such as child abuse and neglect [3,4], are commonly discussed risk factors for drug abuse later in life. Whether socio-economic status (SES) in child- hood also predicts illicit drug abuse in young adulthood has been elucidated less clearly. The systematic literature review by Hickman and colleagues [5] found some indi- cations of an association between low SES in childhood and cannabis use later in life, but the results for cannabis dependence or other more severe forms of drug abuse were not as clear.This finding is also contrasted by more recent research concluding that higher childhood SES is related to higher marijuana use [6]. Other studies, focused on educational factors, have shown that poor school performance is associated strongly with drug abuse [7–10]. A recent report by the Swedish National Agency for Education [11] discusses socio-economic inequality as an important and persistent cause of differences in school performance. It seems fair to assume that the effects of school performance and socio-economic position in childhood on the risk for illicit drug abuse are not altogether independent. This has been indicated in multiple studies [12–16], but only a few have succeeded in disentangling the complex interactions between childhood socio-economic position, school per- formance and drug abuse later in life [17]. Furthermore, most of this research is based on self-reported drug abuse. RESEARCH REPORT doi:10.1111/add.12169 © 2013 Society for the Study of Addiction Addiction