Kaye et al.'s  paper now adds a new page to the history of substance use disorders (SUD) and to the attention deficit hyperactivity disorder (ADHD) comorbidity debate. This well-designed study confirms that ADHD is a frequent comorbidity not only in patients seeking treatment for SUD, but also in adult psychostimulant drug users not undergoing treatment. It was reported that 50% of psychostimulant users who are not receiving treatment screen positive for ADHD . As mentioned in previous studies, in Kaye et al.'s study ADHD comorbid patients present a more severe pattern of drug consumption . The results of the study by Kaye et al. highlight the importance of screening for ADHD in SUD patients, as well as in individuals with SUDs who are not in treatment, and presents the opportunity for further discussion concerning this frequent comorbidity. Is this coincidence self-medication or a conspicuous disorder?
Several series have reported an ADHD/SUD comorbidity [2-7], which certainly does not appear to occur only by coincidence. In previously reported studies, some critics were suspected of possible selection bias . Most of the studies were performed in clinic-referred samples of adults meeting criteria for ADHD or some other condition, such as SUD. Patients undergoing treatment for SUD with a comorbid ADHD diagnosis may not be representative of all adults with SUD. The Kaye et al. study attempts to counteract this argument, evaluating a non-clinical sample of self-reported adult psychostimulant users. As in previous studies, the lack of a comprehensive clinical diagnosis of ADHD for subjects who screened positive remains a limitation of this study. Screening tests may overestimate the prevalence of ADHD due to the presence of false positives.
Considering a prevalence of threefold more patients reporting ADHD symptoms among drug users in the Kaye et al. study, important questions should be raised: does self-medication of ADHD patients with psychostimulants justify the elevated prevalence of ADHD and SUD comorbidity? What comes first, the chicken or the egg? Is SUD preventable if diagnosed at an early stage and treatment for ADHD carried out? Moreover, if safe ADHD treatment is currently available, can under-diagnosing or avoiding the diagnosis or treatment of ADHD be harmful, and result in exposing some children to the development of SUD? Should health-care planners include this comorbidity as a target for the armamentarium of preventive priorities?
Is this a hidden or a conspicuous disorder? Evidence shows that an ADHD diagnosis may be frequently overlooked and not evaluated among SUD patients . Concerns regarding the validity and over-diagnosis of ADHD seem to be still present among health-care professionals world-wide [10-12]. Some clinicians have argued the principle of ‘first do no harm’ when confronted with the decision of prescribing ADHD treatment and prefer not to prescribe any medication. Nevertheless, if ADHD goes hand-in-hand with the development of SUD, not diagnosing or under-diagnosing ADHD may be harmful. Moreover, ADHD treatment by stimulant medication, such as methylphenidate, is both effective and relatively safe [13-15]. Prescribing it may not be as harmful as the eventual development of an SUD. Some authors suggest that the treatment for ADHD in children produces a beneficial effect on the prevention of addictive problems in later life [16, 17].
Extremely provocative perspectives warrant future in-depth investigation into the complexities of AHDH/SUD comorbidity. Prospective studies comparing the prognosis of patients with and without the comorbidity will have important implications in the design of effective treatment for comorbid patients. Moreover, it still remains to be established if ADHD treatment changes SUD prognosis and what the neurobiological interconnections are between these two disorders. Increasing our knowledge of adult ADHD among SUD patients may lead to a targeted therapeutic approach, resulting in improved treatment with better patient outcome.
Declarations of interest