title: Attention-deficit/hyperactivity disorder and risk for substance use disorders in relatives.
abstract: BACKGROUND
  Previous research indicates that attention-deficit/hyperactivity disorder (ADHD) is highly associated with substance use disorders (SUD). However, these studies have failed to clarify the nature of the overlap. The main aim of this study was to explore whether the overlap between ADHD and SUD could be explained by shared genetic and environmental factors or by harmful effects of ADHD medication.
  
  
  METHODS
  We employed a matched cohort design across different levels of family relatedness recorded from 1973-2009. By linking longitudinal Swedish national registers, 62,015 ADHD probands and first-degree and second-degree relatives were identified and matched 1:10 with control subjects without ADHD and their corresponding relatives. Any record of SUD was defined by discharge diagnoses of the International Classification of Diseases or a purchase of any drug used in the treatment of SUD.
  
  
  RESULTS
  First-degree relatives of ADHD probands were at elevated risk for SUD (odds ratios 2.2 and 1.8) compared with relatives of control subjects. The corresponding relative risk in second-degree relatives was substantially lower (odd ratios 1.4 and 1.4). The familial aggregation patterns remained similar for first-degree and second-degree relatives after excluding individuals with coexisting disorders such as schizophrenia, bipolar disorder, depression, and conduct disorder.
  
  
  CONCLUSIONS
  Our findings suggest that the co-occurrence of ADHD and SUD is due to genetic factors shared between the two disorders, rather than to a general propensity for psychiatric disorders or harmful effects of ADHD medication.
authors.affiliation: Departments of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.. Electronic address: charlotte.skoglund@ki.se.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Skoglund
authors.affiliation: Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Qi
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Departments of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Franck
authors.affiliation: Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
authors.affiliation: Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Larsson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology* / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D015897:Comorbidity; D005190:Family; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012042:Registries; D012307:Risk Factors; D012680:Sensitivity and Specificity; D019966:Substance-Related Disorders / Q000453:epidemiology* / Q000235:genetics; D013548:Sweden; D055815:Young Adult
keywords: ADHD; Alcohol use disorder; Comorbidity; Drug abuse; Family study; Substance use disorder