What causes ADHD?

ADHD is a complex condition, and we don’t know exactly what causes it. ADHD is thought to result from the interaction of several factors and that no one single thing causes ADHD.1 Genes
  • We know that ADHD tends to run in families.1,2 If a parent has ADHD, there is more than a 50% chance that a child will have ADHD.3 If an older sibling has it, there is more than a 30% chance that a younger sibling will have it.3
  • While this suggests that genes play a role in the development of ADHD, scientists have not identified a single gene that causes ADHD.1 Rather, interactions among many genes may contribute to the development of ADHD.2
  • Some environmental factors have been linked to an increase in the risk of ADHD.1,2 Just like with genes, however, no single cause can explain all cases of ADHD.2
  • Exposure to certain substances during pregnancy or when a child is very young may be associated with an increased risk of ADHD.2 Researchers continue to try to clarify the nature of these relationships.2
  • Environmental factors that may contribute to the risk of developing ADHD include:

    – Cigarette smoking, alcohol use, or drug use during pregnancy.3

    – Exposure to environmental toxins during pregnancy.2,3

    – Exposure to environmental toxins at a young age.2,3

    • Some environmental toxins that have been studied in ADHD include lead, pesticides, and chemicals used in consumer goods.2-5
  • Low birth weight and brain injuries may also increase the risk of a child developing ADHD.3
Diet Sweets illustration

It is not clear if diet influences the development of ADHD. More sugar in the diet may be associated with worse ADHD symptoms; however, it is not known for sure that the additional sugar is what causes this correlation.2


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