The prevalence of psychiatric comorbidities in adult ADHD compared with non-ADHD populations: A systematic literature review

Attention-deficit/hyperactivity disorder (ADHD) is increasingly recognized in adults, often presenting with complex psychiatric comorbidities that complicate diagnosis and worsen patient prognosis. While individual studies have explored these comorbidities, there has been a lack of comprehensive synthesis comparing ADHD populations directly with non-ADHD populations. The researchers conducted a systematic literature review following PRISMA guidelines to identify and analyze studies published between 1990 and 2022. They categorized 32 identified studies into three groups: general populations, clinical populations (patients already in psychiatric care), and incarcerated populations.

The review consistently found that comorbid psychiatric disorders are more prevalent in adults with ADHD than in those without, regardless of whether the study was conducted in a general or clinical setting. Substance use disorders (SUD) were the most frequently identified comorbidity, with prevalence rates reaching up to 82.9% in some clinical samples. Mood disorders, including depression and bipolar disorder, were also highly prevalent, alongside various anxiety and personality disorders. The researchers observed substantial variation in how these comorbidities were reported, which they attributed partly to the inconsistent use of ADHD diagnostic instruments, such as the Adult ADHD Self-Report Scale (ASRS) versus clinical interviews like the CAADID.

Recognizing the high frequency of co-occurring psychiatric conditions is essential for clinicians working with adult patients. The findings suggest that when a patient presents with multiple psychopathologies—particularly substance abuse or mood instability—there may be an underlying, undiagnosed ADHD component. The study highlights the urgent need for standardized diagnostic tools for adult ADHD to reduce current variability in prevalence reports, improve differential diagnosis, and facilitate earlier, more effective clinical interventions.