To collect and describe available literature exploring the association between adult ADHD and the risk of developing dementia.

Attention-deficit/hyperactivity disorder (ADHD) often persists into adulthood. Emergent studies suggest an association between adult ADHD and dementia. However, longitudinal data assessing whether ADHD influences dementia risk remain scarce.

A scoping review was performed following PRISMA-ScR guidelines. PubMed/MEDLINE, Scopus, EMBASE, and PsychINFO were searched for English- and Spanish-language studies (2010-2025). Eligible designs included cohort, case-control, and cross-sectional studies; preclinical and pediatric population studies were excluded. Screening was performed in Covidence. Outcomes evaluated: ADHD-treatment history, global cognition, domain scores, and dementia incidence/prevalence.

Seven studies (n=2,683,190) were included: five cohorts, one case-control, and one cross-sectional. All studies compared adults with ADHD to matched controls with 5–17 years of follow-up. Diagnoses were established via clinical assessment, validated tests, and ICD codes. Four cohorts found elevated dementia incidence in ADHD, with HRs ranging from 2.77 to 4.01, all statistically significant. A multigenerational cohort showed increased parental dementia risk (HR 1.55, 95% CI 1.26–1.89, p<.001). Two studies associated ADHD with Lewy Body Dementia (IRR 1.21, 95% CI 1.08–1.35, p<.001; OR 5.1, 95% CI 2.7–9.6, p<.001), and one with Alzheimer’s disease (IRR 1.15, 95% CI 1.05–1.27, p<.001). Three studies reported Mini-Mental State Examination scores, consistently lower among ADHD patients (means 21.7–28.5). One study found no significant protective association of ADHD treatment with dementia risk.

Adults with ADHD exhibit a higher risk of dementia across diverse populations, though heterogeneity in diagnosis and limited treatment evidence highlight the need for rigorous longitudinal research.