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 gene⁶ Genes are the basic units by which inherited information is passed from a parent to a child. A child inherits one copy of each gene from their mother and one copy from their father. 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

Environment

• 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 environmental toxin⁷ An environmental toxin is a small amount of a poison that is found in the air, water, food, etc. 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

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