Question
Does ADHD affect IQ?
Short answer
ADHD is not diagnosed with an IQ test, and people with ADHD can have any level of intelligence. On average, groups with ADHD score somewhat lower on IQ tests than comparison groups (a 2004 meta-analysis found d = .61), but that is an average gap with wide overlap. ADHD is also a valid diagnosis in people with high intelligence.
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This page is general information, not medical advice. If you have questions about ADHD for yourself or a child, talk to a qualified clinician.
How ADHD is diagnosed
NIMH describes ADHD as a neurodevelopmental disorder marked by inattention, hyperactivity and impulsivity (NIMH ADHD topic). For a diagnosis, symptoms must begin before age 12, last at least six months, appear in two or more settings and interfere with functioning (NIMH ADHD brochure 2024). Evaluations usually rely on history, observations from people who know the person, and standardized behavior rating scales or symptom checklists (NIMH ADHD brochure 2024). An IQ score is not one of the criteria. NIMH also states plainly that anyone can have ADHD (NIMH ADHD brochure 2024).
Where IQ tests come in
Cognitive testing can still be part of an evaluation. NIMH says such tests are used to identify strengths and challenges and to identify or rule out learning disabilities (NIMH ADHD brochure 2024). A profile of index scores, for example working memory and processing speed on a Wechsler test, can show where a person struggles and where they are strong.
Try one · Logical Reasoning
Which tile completes the second pair?
Tap the option you think is right, or show the answer.
Show the answer
The missing panel shows a large hatched circle, with small solid shapes: a diamond at the bottom-right corner and a diamond at the right side (option 6).
How to solve it
- Compare the first two panels and name exactly what changed.
- The main shape and the small shapes swap forms: the main shape takes the form of the small ones, and the small ones take the form of the main shape.
- Nothing else changes.
- Apply the same change to the third panel: a large hatched diamond, with small solid shapes: a circle at the bottom-right corner and a circle at the right side.
- So the missing panel shows a large hatched circle, with small solid shapes: a diamond at the bottom-right corner and a diamond at the right side.
That was 1 puzzle. The full test has 25.
What research finds about averages
A 2004 meta-analysis found that groups with ADHD scored lower on average than healthy comparison groups on Full Scale IQ, with a weighted effect size of d = .61 (Frazier, Demaree and Youngstrom 2004). In plain terms, that is a moderate average difference, a bit over half a standard deviation, with a great deal of overlap between the groups. The same analysis found the IQ gap was significantly smaller than the gaps on spelling and arithmetic achievement tests (Frazier, Demaree and Youngstrom 2004).
An average gap between groups says nothing about any one person. Many people with ADHD score well above average.
High ability and ADHD together
A 2016 systematic review concluded that ADHD is a valid diagnosis in people with high intelligence, although the evidence base is limited (Rommelse et al. 2016). It notes two opposite risks: high intelligence may mimic some ADHD symptoms, and highly intelligent people may compensate in ways that cause ADHD to be missed (Rommelse et al. 2016). Students with both high ability and a disability are often called twice-exceptional; see what twice-exceptional means.
A note on online tests
An online IQ estimate, including ours, cannot diagnose or rule out ADHD and cannot be used for any disability assessment. If attention made a timed test hard on the day, that tells you about the conditions, not your ceiling. For what an IQ score does measure, see what IQ is and working memory.
Sources
- National Institute of Mental Health, Attention-Deficit/Hyperactivity Disorder (ADHD), health topic page www.nimh.nih.gov/health/topics/attention-deficit-hyperactivity-disorder-adhd
- National Institute of Mental Health, Attention-Deficit/Hyperactivity Disorder: What You Need to Know, NIH Publication No. 24-MH-8300, revised 2024 www.nimh.nih.gov/health/publications/attention-deficit-hyperactivity-disorder-what-you-need-to-know
- Frazier, T. W., Demaree, H. A., & Youngstrom, E. A., Meta-analysis of intellectual and neuropsychological test performance in attention-deficit/hyperactivity disorder, Neuropsychology 18(3), 543 to 555, 2004, PMID 15291732 doi.org/10.1037/0894-4105.18.3.543
- Rommelse, N., van der Kruijs, M., Damhuis, J., et al., An evidenced-based perspective on the validity of attention-deficit/hyperactivity disorder in the context of high intelligence, Neuroscience and Biobehavioral Reviews 71, 21 to 47, 2016, PMID 27590827 doi.org/10.1016/j.neubiorev.2016.08.032