by Chuck Ruby, PhD

An October 2023 JAMA Network Open article titled “Adult Attention-Deficit/Hyperactivity Disorder and the Risk of Dementia” concludes that an “adult ADHD diagnosis was associated with a 2.77-fold increased dementia risk” and there was “no clear increase in the risk of dementia associated with adult ADHD among those who received psychostimulant medication.” In this study, more than 100,000 subjects were followed over a 17-year period and identified as having been diagnosed with ADHD, dementia, or both ADHD and dementia during that time.

The study was also covered by the Washington Post with the headline: “Adult ADHD may take a toll on the brain.” The Post article also pointed out the claim that stimulant drugs can lessen the risk.

This is one of many such announcements by professional journals and public news outlets that are misleading and that perpetuate the myth of mental illness as a brain disorder. Based on the data in this study, it is not justified, and might very well be harmful, to publicly proclaim that those who have been diagnosed with ADHD are at increased risk of getting dementia as a result of some negative affect that ADHD has on the brain. Not only does it encourage the false belief that ADHD is a real neurodevelopmental disorder - some kind of brain dysfunction - similar to dementia, it also promotes alarm and leads people to think stimulant drugs can prevent dementia for those who have been diagnosed with ADHD. 

There are two serious problems with the study’s conclusions. The first is that correlation does not equal causation. We are continually cautioned about this; nevertheless, many people, especially the lay public, hear causal implications in correlational results. In the present study, the manner in which the information is presented clearly suggests that ADHD causes an increased risk of dementia. But this is not a justified interpretation. Whereas they could have something to do with each other (see below), it also could be that ADHD and dementia have nothing to do with each other. Instead, they could be spuriously correlated because of their independent association with other variables. Consider as examples the many strong yet spurious (and quite silly) correlations at http://www.tylervigen.com/spurious-correlations.

Furthermore, the study reported a 2.77-fold increased dementia risk. This means those who were diagnosed with ADHD had a 177% higher risk of getting dementia than those who were not diagnosed with ADHD. However, the 177% is misleading. Whereas it is accurate, it is a relative risk figure. In other words, it is measuring the difference between two relatively low absolute risk figures: a 7% risk of dementia for those never diagnosed with ADHD; and 13.2% risk for those diagnosed with ADHD.* In actuality, the absolute percentage point increase for those diagnosed with ADHD is only 6.2%, a far less serious message than saying there is a 177% increase in the risk.

The second problem is that the symptoms of dementia are very similar to the diagnostic criteria of ADHD. This weakens the confidence we can have that a diagnosis of either is accurate and has resulted in discriminative validity problems. See https://www.frontiersin.org/articles/10.3389/fnagi.2017.00260/full and https://wchh.onlinelibrary.wiley.com/doi/full/10.1002/pnp.784. Think about how much overlap there is among the following symptoms (from the Mayo Clinic website for dementia and ADHD) and how a practitioner could interpret them as indicative of either problem. 

In other words, someone who is developing dementia might be mistakenly diagnosed with ADHD. Likewise, someone who doesn’t have dementia, but who is demonstrating the criteria for ADHD, might be mistakenly diagnosed with dementia. This would explain the correlation between the two found in the JAMA study. In essence, rather than interpreting the correlation as indicative of one condition increasing the risk of the other, one is the other. 

Relatedly, the finding of no increased dementia risk for those diagnosed with ADHD and who used stimulant drugs, merely demonstrates that stimulants increase one’s attention abilities. They help one focus better on tasks. But that is what stimulants do - for all people. Anyone who is a coffee aficionado knows this. Those who used stimulant drugs would have artificially enhanced their attention capacity to the point of reaching sub-threshold levels of ADHD criteria, and thus, it would be less probable that they would have been mistaken as dementia patients.

These kind of studies, whether they are about ADHD, depression, bipolar disorder, or any other mental disorder category, are replete with similar problems. Those problems are based largely in how language is used to imply that mental disorder is some type of “dysfunction within the individual,” as is claimed in the DSM (p. 20), how this “disease-ifies” common difficulties, and how statistics are used to inflate the practical importance of the results. We must be on guard to call out these announcements. 

*The 177% increased risk is based on the adjusted hazard ratio of 2.77 presented in the study, even though the actual relative risk increase between the absolute risks of dementia for those diagnosed with ADHD and those with no diagnosis is 189% (13.2% / 7%).

Chuck Ruby, PhD, is a psychologist who has been in private practice for the past 25 years, after a 20-year career with the U.S. Air Force. You can read more about him at his personal website. He is the author of Smoke and Mirrors: How You Are Being Fooled About Mental Illness - An Insider's Warning to Consumers. Dr. Ruby is the past Chairperson of the Board for ISEPP and has been the Executive Director since 2015.