Attention-deficit/hyperactivity disorder (ADHD) and major depressive disorder (MDD) are separately common mental health conditions that can have an adverse effect on a patient's quality of life if left untreated. These disorders frequently cooccur with one another, which can lead to increased patient suffering and diagnostic challenges for the treating clinician. In the United States adult population, epidemiological data show that the prevalence rate for MDD is 6.7%, while the ADHD prevalence rate in US adults is 4.4%. This epidemiological data represents the general population and likely underestimates the prevalence rates in clinic or practice patients. Examining the concurrent comorbid rate, if a patient has MDD, the likelihood of that patient also having ADHD is 18.6%; if the patient has ADHD, the likelihood of that patient having comorbid MDD is 9.4%. If the patient has dysthymia, the comorbid rate of ADHD is 12.8%, while those adults with ADHD have a comorbid rate of dysthymia of 22.6% (Slide 1).

The diagnostic distinction between ADHD and MDD is a critical aspect of clinical evaluation that often presents challenges and confusion to the treating clinician (Slide 2). There are several factors that clinicians should consider in order to best distinguish these disorders, and ensure an accurate diagnosis—age of symptom onset, presenting symptoms, and family history of either disorder.

Typically, ADHD presents first in children, whereas most mood disorders, specifically MDD, have their index case onset in adolescence. Although MDD and dysthymia is reported in childhood, the peak incidence occurs during the adolescent years. Thus, the age of onset becomes one diagnostic factor that can assist in distinguishing these two conditions.

During the past decade, a similar composite has emerged for both bipolar disorder and adult attention-deficit/hyperactive disorder (ADHD). First, both conditions have a relatively high prevalence, a low case detection, a protracted illness course, a high rate of comorbidity, multifactorial ideology, substantial heritable liability, and tremendous burden of illness in economic cost as well as interpersonal and vocational maladjustments. What has also been interesting along with these reports is that there has been emerging scientific studies implicating common brain regions and neural circuits subserving essential features of both conditions.

In examining the challenges in treating comorbid attention-deficit/hyperactivity disorder (ADHD) and substance use disorder (SUD), there are a number of issues regarding misinformation and misconception that exist for clinicians. Like other ADHD comorbidities, there is a lack of screening, particularly among adult clinical populations who have the psychiatric comorbidity or, for patients with SUDs, there is the issue of prioritization, which condition to treat first, and determining the place of medication management—particularly stimulant medication—paramount in treatment planning.