1.7 Causes of ADHD

ADHD has been researched extensively in the United States and a number of countries throughout the world. Sophisticated brain-imaging technologies and genetic research in recent years, particularly since the mid-2000s, has dramatically increased our knowledge of the probable causes of ADHD.

We now know there are multiple causes, although we certainly do not know all of them. Based on hundreds of well-designed and controlled scientific studies, the evidence clearly suggests that ADHD is the result of brain differences: abnormalities in size, maturation, and levels of activity in the regions of the brain involved in executive functions and self-regulation.

Heredity is the main known cause of ADHD, accounting for most cases. In other cases, there are problems and factors that occur prenatally, during birth, or in childhood that might interfere with a child's brain development and be contributing causes of ADHD.


  • Based on the evidence, heredity is the most common cause of ADHD, accounting for approximately 75 to 80 percent of children with this disorder (Barkley, 1998, 2013a).
  • ADHD is known to run in families, as found by numerous studies (twin studies with identical and fraternal twins, adopted children, family studies, molecular genetic studies). For example, in studies of identical twins, if one has ADHD there is as high as a 75 to 90 percent chance that the other twin will have ADHD as well (Barkley, 2013a).
  • It is believed that a genetic predisposition ...

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