ADHD News & Research

Finding: Prevalence of ADHD High in Psychiatric Outpatient Clinics

The prevalence of ADHD among patients at psychiatric outpatient clinics is 15% to 27%, according to a study that found undiagnosed and untreated symptoms common among patients seeking care for comorbid conditions.

April 15, 2021

At least one in seven adult patients of psychiatric outpatient clinics has symptoms of ADHD — more than 5 times the rate found in the general population — according to a recent systematic review and meta-analysis published in the Journal of Attention Disorders. After administering ADHD screening tests to patients, the clinics found that one in four adults demonstrated symptoms of ADHD. More detailed assessments, including interviews, revealed a slightly lower ADHD prevalence rate of 15% among adult patients, most of whom were not previously diagnosed. 1 The prevalence of ADHD in the general adult population worldwide is 2.8%. 2

“The higher rate found in psychiatry outpatient clinics may be explained by the high rates of psychiatric comorbidity among adult ADHD,” the study authors wrote. “Untreated childhood ADHD is known to be a risk factor for subsequent mental illness, including depression, conduct disorder, and substance misuse. There is some suggestion that this is both a shared genetic liability and a causal relationship.”

The new meta-analysis is based on data from 1,593 males (267 diagnosed with ADHD), and 1,809 females (295 diagnosed with ADHD) found in a systematic review of databases held by PubMed, EBSCO, CINAHL Complete, Scopus, and EMBASE using ADHD-related keywords.

The authors reported that age and gender did not seriously impact the estimated prevalence of ADHD in patients of psychiatric outpatient clinics. However, excluding individuals with psychosis increased the rates of ADHD found through screenings and in-depth assessments, the study found.

The screening scale used also influenced rates of ADHD found. The systematic review and meta-analysis showed that ADHD was found to be more prevalent when evaluators used the DSM-5 criteria, and less prevalent when they used the older DSM-IV criteria. 1,2

“The most concerning finding is that only a small fraction of adults with ADHD are diagnosed within the mental health services,” the authors wrote. “Of equal concern is the report that the majority of ADHD cases were undiagnosed, and as such unlikely to be treated. Individuals with unrecognized ADHD might present to adult services with related or comorbid symptoms, which may take precedence in diagnosis and subsequent treatment. It was suggested that treatment efficacy of other disorders is limited when the underlying ADHD is not treated.” 3,4,5,

The authors continued, “more studies are needed to have a greater body of evidence, and a more precise estimate of the prevalence of ADHD in adult outpatient psychiatric clinics.”

View Article Sources

1Adamis, D., Flynn, C., Wrigley, M., Gavin, B., & McNicholas, F. (2022). ADHD in Adults: A Systematic Review and Meta-Analysis of Prevalence Studies in Outpatient Psychiatric Clinics. Journal of Attention Disorders.//

2ADDitude Editors (April 5, 2022). ADHD Statistics: New ADD Facts and Research. ADDitude.//

3Adamis, D., Graffeo, I., Kumar, R., Meagher, D., O’Neill, D., Mulligan, O., Murthy, S., O’Mahony, E., McCarthy, G., Gavin, B., McNicholas, F. (2018). Screening for attention deficit-hyperactivity disorder (ADHD) symptomatology in adult mental health clinics. Irish Journal of Psychological Medicine, 35(3), 193–201.//

4Deberdt, W., Thome, J., Lebrec, J., Kraemer, S., Fregenal, I., Ramos-Quiroga, J. A., Arif, M. (2015). Prevalence of ADHD in nonpsychotic adult psychiatric care (ADPSYC): A multinational cross-sectional study in Europe. BMC Psychiatry.//

5Nylander, L., Holmqvist, M., Gustafson, L., Gillberg, C. (2009). ADHD in adult psychiatry. Minimum rates and clinical presentation in general psychiatry outpatients. Nordic Journal of Psychiatry.63(1), 64–71.//