Attention deficit hyperactivity disorder and substance misuse: an evaluation of causal hypotheses and treatment considerations

Abstract

Attention deficit hyperactivity disorder (ADHD) is known to co-occur with substance misuse at a high rate. This has important health and legal implications for those with ADHD. Mechanisms that may influence drug use among those with ADHD are discussed and evaluated in this review, including self-medication, behavioral disinhibition, comorbidity, and sensitization. While no one hypothesis is able to explain the complex phenomenon of drug taking behaviors, it is likely that self-medication, disinhibition and comorbidity play a part, with little evidence for sensitization. The development of efficacious treatment is necessary to help those with this debilitating comorbidity, as there are currently few evidence-based interventions.

Keywords:

• attention deficit hyperactivity disorder
• behavioral disinhibition
• comorbidity
• drugs
• self-medication
• sensitization
• stimulant
• substance use
• treatment

Acknowledgement

The authors would like to thank Dr Aisling Parsons and the ICASA project for their help with identifying relevant literature.

Financial & competing interests disclosure

S Young has received honoraria for consultancy, travel, educational talks and/or research from Janssen, Eli Lilly, Shire, Novartis, HB Pharma, Flynn Pharma and/or Shire. O Sedgwick receives funding support from the National Institute for Health Research (NIHR) Mental Health Biomedical Research Centre at South London and Maudsley National Health Service (NHS) Foundation Trust and King’s College London. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key issues

• The comorbidity of attention deficit hyperactivity disorder (ADHD) and substance use disorders (SUD) is prevalent, and is associated with poor employment, health, and legal outcomes.

• The self-medication hypothesis purports that individuals engage in substance use in an attempt to treat ADHD symptoms. This is biologically plausible and supported by studies showing those with more ADHD symptoms use more drugs; however, individuals with ADHD do not cite this as a motivator more often than individuals without ADHD.

• The behavioral inhibition hypothesis suggests that difficulties in controlling or regulating behaviors results in substance use. While there is little evidence to support the assertion that neuropsychological deficits (e.g., executive dysfunction) are associated with substance abuse in an ADHD group, there is evidence to suggest sensation seeking and reactive disinhibition may be associated with substance misuse.

• The comorbidity hypothesis posits that comorbid disorders (which are highly prevalent in ADHD) drive substance abuse in this population, as opposed to specific ADHD symptoms. For example, comorbid conduct disorder is implicated in the development of substance use, which may represent a signal for early intervention. There are high rates of externalizing disorders among those with ADHD and SUD, and these may be associated with substance misuse via novelty seeking. In addition, self-medication of internalizing disorders may play a role.

• The sensitization hypothesis suggests that early use of stimulant medication makes later use of drugs more pleasurable due to the alteration of dopaminergic transmission. There is little evidence from human studies to support this, and most studies support a protective, or a neither protective nor risk-enhancing, effect of early stimulant use on later substance use among those with ADHD.

• Treatment of this comorbid group with stimulant medication is not well supported, but there have been relatively few randomized controlled trials.

• Psychological intervention appears promising, and randomized controlled trials which have combined medication and psychological therapies show improvement in both drug and placebo arms, suggesting that the therapy is mediating this effect.

• Future research should focus on elucidating causal pathways in an effort to identify early intervention strategies, and on developing and assessing the efficacy of psychological interventions.