What causes Attention Deficit Hyperactivity Disorder (ADHD)?

From the Guidelines

The exact cause of ADHD (Attention-Deficit/Hyperactivity Disorder) remains unknown, but research indicates it's primarily a neurobiological condition with strong genetic influences, as stated in the most recent study 1. ADHD results from differences in brain structure and function, particularly in areas controlling attention, impulse control, and executive functioning. Genetic factors play a significant role, with ADHD having a high heritability rate, meaning children with a parent or sibling with ADHD have a higher likelihood of developing the condition. Environmental factors may also contribute, including prenatal exposure to substances like alcohol, tobacco, or certain medications, premature birth, low birth weight, and exposure to environmental toxins such as lead. Brain injury or certain infections during early development might increase risk in some cases. Contrary to popular misconceptions, parenting styles, excessive sugar consumption, or too much screen time do not cause ADHD, though they may exacerbate symptoms in those who already have the condition. Some key points to consider when evaluating the cause of ADHD include:

• The role of genetic factors, with a heritability rate of approximately 74% 1
• The impact of environmental factors, such as prenatal exposure to substances or premature birth 1
• The importance of considering comorbid conditions, such as emotional or behavioral conditions, developmental conditions, and physical conditions 1
• The need for a comprehensive evaluation, including a process to at least screen for comorbid conditions 1 ADHD is a complex neurodevelopmental disorder resulting from the interplay of genetic predisposition and environmental influences affecting brain development and functioning, as supported by the most recent and highest quality study 1.

From the FDA Drug Label

The specific etiology of ADHD is unknown, and there is no single diagnostic test.

The cause of Attention Deficit Hyperactivity Disorder (ADHD) is unknown. 2

From the Research

Causes of Attention Deficit Hyperactivity Disorder (ADHD)

The causes of ADHD are complex and multifaceted, involving both genetic and environmental factors. Some of the key factors that contribute to the development of ADHD include:

• Genetic predisposition: Studies have shown that ADHD has a high heritability, with estimates suggesting that genetic factors account for approximately 76% of the risk 3.
• Brain structure and function: Research has found that individuals with ADHD tend to have smaller brain volumes, particularly in the prefrontal cortex, basal ganglia, and cerebellum 4, 5, 6, 7.
• Neurotransmitter imbalance: Dysregulation of neurotransmitters such as dopamine and norepinephrine has been implicated in the pathophysiology of ADHD 4, 5, 7.
• Environmental factors: Environmental factors, such as exposure to toxins and prenatal smoking, may also contribute to the development of ADHD 6.

Genetic Factors

Genetic studies have identified several candidate genes that may contribute to the development of ADHD, including:

• DRD4: A gene involved in dopamine signaling 3.
• DRD5: A gene involved in dopamine signaling 3.
• DAT1: A gene involved in dopamine transport 3.
• HTR1B: A gene involved in serotonin signaling 3.
• SNAP25: A gene involved in synaptic transmission 3.

Neurobiological Factors

Neurobiological studies have found that ADHD is associated with:

• Reduced connectivity in white matter tracts in key brain areas 4.
• Impairment of executive function and the reward system 5.
• Dysfunction of the default mode network 5.
• Weaker function and structure of prefrontal cortex (PFC) circuits, especially in the right hemisphere 7.