What Are the Possible Causes of ADHD?

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The exact origin of ADHD is unknown, but researchers believe the disorder may be caused by one or more of the following factors:

Brain Chemistry

ADHD is thought to be caused by an imbalance of two chemical messengers, or neurotransmitters, in the brain. Researchers think that these chemicals might play an important role in ADHD. You can learn more about ADHD and the brain below.


Research suggests that ADHD tends to run in families. However, this does not mean that all children in a family will have the disorder. You can track ADHD symptoms in your family by completing Your Family Tree.


Certain external factors, such as smoking during pregnancy or complications during pregnancy, delivery, or infancy, may contribute to ADHD.

What parts of the brain are thought to be involved in ADHD?

We do not know exactly why people develop ADHD. It may be related to problems with a part of the brain called the prefrontal cortex. The picture below shows the different parts of the prefrontal cortex that control attention, behavior, and judgment. Certain regions of the prefrontal cortex may not function properly in people with ADHD.

The 3 Subregions of the Prefrontal Cortex Thought to be Related to the 3 Core Symptoms of ADHD.

If the areas of the prefrontal cortex shown in green, blue, or brown are impaired, a person with ADHD may have symptoms such as inattention or impulsive or hyperactive behavior.

You can learn more by watching this videovideo.