IQ and ADHD

Does ADHD affect IQ test scores? Yes, but only slightly—people with ADHD average about 3–4 points lower. Discover why IQ tests remain accurate for ADHD and what really impacts results.

Dr. Russell T. WarneChief Scientist

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental condition marked by inattention, impulsivity, and hyperactivity that interfere with daily functioning. Because the difficulties with attention and behavioral regulation can impact IQ test performance, there has been a great deal of interest in whether ADHD impacts intelligence.

Years of research have shown that individuals with ADHD can have IQs across the full spectrum, from very low to exceptionally high. On average, there is a slightly lower IQ for people with ADHD: in one study of nearly 2,000 people, the IQ of people with ADHD was 3.75 points lower than the average IQ of people without ADHD. This is a small difference that would only be noticed in large samples of people. In fact, the authors stated that it was “. . . small and not clinically meaningful.”

How ADHD Affects Test Performance

Even a difference of 3.75 IQ points does not necessarily mean that the (slightly) lower scores that people with ADHD obtain on IQ tests is an indication that they are slightly less intelligent. Some of this difference may be due to the ADHD interfering with performing the specific tasks on the test without impacting the person’s general intelligence. Tasks that require sustained focus or working memory may be weaker than those measuring reasoning or verbal comprehension.

It is hard to estimate how much of the difference is due to the ADHD acting as an interfering variable and how much is due to a true difference in intelligence. Currently, it is best to see the difference of 3.75 IQ points as a maximum intelligence difference (which may possibly be much smaller). This is good news because if 3.75 IQ points is “small and not clinically meaningful,” then the “real” intelligence difference might be even smaller and less meaningful.

Findings From Research

Psychologists are in the process of determining how ADHD interferes with problem solving. One study experimentally demonstrates in school-aged children that slow cognitive processing speed is a plausible cause of working memory (WM) deficits in ADHD, consistent with the time-based resource-sharing model of WM. The results offer a mechanistic account of this relationship, urging clinical research to explore non-executive processes in the etiology of ADHD.

Executive functions like planning, organization, working memory, and impulse control are commonly impaired in ADHD. These abilities govern how intelligence is applied in daily life. A person with strong reasoning but poor executive control may underperform academically, while one with moderate reasoning and good organization may achieve consistent success. Understanding this interaction helps clinicians distinguish between intellectual ability and difficulties in self-management.

The Role of IQ Testing in ADHD Evaluation

IQ assessments assist in clarifying whether performance issues stem from attention deficits or broader cognitive limitations. This information helps guide educational and therapeutic planning. However, IQ tests, by themselves, cannot diagnose ADHD. Instead, ADHD diagnosis relies on comprehensive evaluation, including behavioral observation and developmental history.

ADHD alters how attention and behavior are regulated. IQ tests help clinicians observe attention and other behaviors in a standardized setting, which provides a clearer picture of cognitive strengths and weaknesses. Psychological tests developed under professional standards can separate intellectual potential from attentional control. Recognizing this distinction enables fairer assessment and more effective educational and clinical support.

Watch “Why Your Culture Affects Your Brain” with Ivan Kroupin on the Riot IQ YouTube channel to understand how environment and attention shape cognitive performance.