Elsevier

Biological Psychiatry

Volume 77, Issue 10, 15 May 2015, Pages 880-886
Biological Psychiatry

Archival Report
Attention-Deficit/Hyperactivity Disorder and Risk for Substance Use Disorders in Relatives

https://doi.org/10.1016/j.biopsych.2014.10.006Get rights and content

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.

Section snippets

Data Sources

We used data from a record linkage of six population-based registries in Sweden; personal identification numbers enabled accurate linkage (23). The National Patient Register (NPR) provides data on psychiatric inpatient care since 1973 (International Classification of Diseases (ICD)-8 to ICD-10) and outpatient care (ICD-10) since 2001 (24). The Swedish Prescribed Drug Register (PDR) (25) contains information on drug identity (Anatomical Therapeutic Chemical [ATC] codes) and dates of all

Results

Table 1 shows distribution for study variables among ADHD probands, matched control subjects, and their corresponding relatives and ORs for ADHD associated with each comorbid disorder. The ADHD probands were more likely to have been diagnosed with SUD, drug abuse, and alcohol use disorder compared with control subjects matched for age, sex, and residency (ORSUD 10.8 and 95% CI, 10.5–11.1; ORDrug 19.2 and 95% CI, 18.5–19.8; ORAlc 8.3 and 95% CI, 8.0–8.5).

Table 2 shows the numbers and percentages

Discussion

This population-based, case-cohort study found a strong familial association between ADHD and SUD. Our results show that the risk for SUD increases considerably with increased genetic relatedness to an ADHD proband. The familial aggregation patterns remained similar after excluding case subjects and control subjects with SUD as well as relatives with an ADHD diagnosis and support the hypothesis that the association between ADHD and SUD is explained by shared familial risk factors rather than

Acknowledgments and Disclosures

The work was supported by the regional agreement on medical training and clinical research Grant No. K1426-2011 between Stockholm County Council and Karolinska Institutet, the Swedish Research Council Grant Nos. 2010-3184 and 2013-2280, and the Swedish Initiative for Research on Microdata in the Social And Medical Sciences framework Grant No. 340-2013-5867.

CS had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data

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