If one modifies the diagnostic criteria of ADHD and defines the age of onset of ADHD symptoms at 12 (instead of 7 years), then ADHD is very frequent among obese individuals. 27.4% of all patients with obesity also had ADHD. Severe obesity (BMI over 40) had an even higher frequency of ADHD (42.6% of this treatment group). These patients with both obesity and ADHD had more hospitalisation and longer treatments with lower response rates.

Up to now, very little systematic research is available and only few psychotherapists or doctors will do an evaluation for ADHD in this group of patients with eating disorder.

The reasons why ADHD and obesity often occur together are unknown. There are clues that neurotransmitter changes in the dopamine system and reward centres of the brain are affected.