Adults With ADHD May Be at Higher Risk of Developing Dementia

A study of more than 100,000 individuals has found that adults diagnosed with ADHD appear to have almost three times the risk of being diagnosed with dementia later in life, compared to those without ADHD.

As health systems grapple with rising dementia prevalence, attention is increasingly shifting upstream — toward earlier-life factors that may shape long-term cognitive trajectories. One emerging area of focus is attention-deficit/hyperactivity disorder (ADHD), following new evidence suggesting a substantial association with later dementia risk.

A large observational study based on the medical records of more than 100,000 individuals has found that adults diagnosed with ADHD appear to have almost three times the risk of being diagnosed with dementia later in life, compared with those without ADHD. While the findings do not establish causation, the scale of the dataset and the magnitude of the association raise important questions for clinicians, policymakers, and health system planners.

"It is never too early or too late to diagnose and treat ADHD."

- Dr Daniela Tomus - Consultant Psychiatrist - Montrose Health Group

"This is because we can see the negative consequences of untreated ADHD as different presentations, depending on age, but we also see the benefits of treating ADHD. By treatment I understand not only the medication, but the complex psychosocial interventions which are beneficial in managing the symptoms. Ideally the treatment starts in early childhood, to prevent the impact in education and support the appropriate development of cognitive function, but even at old age the negative consequences of untreated ADHD can cumulate and being treated can prevent further deterioration."

The Significance

ADHD is classified in the Diagnostic and Statistical Manual of Mental Disorders as a neurodevelopmental condition, with onset in childhood. However, growing recognition of adult ADHD — often diagnosed decades after symptoms first emerge — has expanded the population under study and reframed ADHD as a lifespan condition rather than a childhood-limited one.

The study followed a large adult cohort over many years, excluding individuals with prior diagnoses of ADHD or dementia at baseline. Those later diagnosed with ADHD in adulthood showed a markedly higher incidence of dementia diagnoses over the follow-up period.

After adjusting for age, sex, socioeconomic status, cardiovascular disease, depression, and lifestyle variables, the association persisted. The central finding remains clear: an almost threefold increase in dementia risk among adults diagnosed with ADHD.

From a health-system perspective, the importance lies less in the precise risk estimate and more in the consistency and scale of the signal.

Understanding the Association

It is essential to distinguish between association and causation. Dementia, including Alzheimer’s disease, is defined by progressive neuronal loss. ADHD, by contrast, is non-progressive.

The prevailing interpretation is therefore not that ADHD causes dementia, but that ADHD may act as a long-term risk modifier, interacting with other determinants of cognitive ageing across decades.

Adults with untreated or late-diagnosed ADHD have higher prevalence of factors independently associated with dementia risk, including:

• Chronic stress and sustained cortisol exposure

• Sleep disruption

• Depression and anxiety

• Cardiometabolic risk factors

• Difficulty sustaining preventive health behaviours

Over long time horizons, the cumulative effect of these factors may increase vulnerability to later cognitive decline.

Late Diagnosis and Cognitive Reserve

A notable feature of the findings is the focus on adult-diagnosed ADHD, which in most cases reflects delayed recognition rather than late onset.

This has implications for cognitive reserve — the brain’s ability to compensate for age-related or pathological change. Cognitive reserve is shaped by education, occupational complexity, sustained mental engagement, and social participation across the life course.

Executive dysfunction associated with untreated ADHD can disrupt these pathways, not through reduced cognitive ability, but through reduced opportunity to build long-term resilience. From this perspective, ADHD may indirectly influence dementia risk by shaping life trajectories that affect brain health decades later.

Treatment Exposure: An Emerging Consideration

One of the more policy-relevant aspects of the data concerns treatment. In subgroup analyses, the elevated dementia risk was not clearly observed among individuals with recorded exposure to ADHD medication, though the evidence is not yet definitive.

This raises an important strategic question: could effective ADHD assessment and treatment reduce long-term cognitive risk by improving sleep, reducing stress, supporting stable routines, and enabling better engagement with healthcare over time?

If supported by future research, this would have implications for adult ADHD service provision, long-term cost-effectiveness modelling, and dementia-prevention strategies.

Implications for Health Systems and Individuals

The association between adult ADHD and an almost threefold increase in dementia risk does not warrant alarm. It does, however, reinforce the need for lifespan-based approaches to brain health, rather than models that separate neurodevelopmental and neurodegenerative conditions.

For individuals, the implication is equally clear: earlier recognition and appropriate management of ADHD may matter not only for day-to-day functioning, but for long-term cognitive health.

A Practical Next Step

For adults who recognise longstanding difficulties with attention, organisation, or executive function — particularly those diagnosed later in life — timely assessment is an important first step.

Here at Montrose Health Group we can provide comprehensive adult ADHD assessments grounded in current evidence and best practice, supporting individuals to understand their diagnosis, access appropriate treatment, and take a proactive approach to lifelong brain health.

As evidence increasingly points to the long-term implications of untreated ADHD, early and accurate diagnosis should be seen not only as a quality-of-life intervention, but as part of a broader preventative health strategy.