What Causes ADHD?

The causes of ADHD have yet to be firmly established. However, recent research suggests that there is some inherited genetic vulnerability to ADHD. For siblings of children with ADHD, the risk of having ADHD is more than doubled, and children with ADHD are four times more likely to have a parent with ADHD symptoms than children without ADHD. Research documenting that certain abnormalities in brain structure and function occur more often in people with ADHD than in the general population supports other biological mechanisms underlying ADHD. For example, studies using magnetic resonance imaging (MRI) have found that the brains of people with ADHD tend to be slightly smaller than those of the general population. Similarly, studies indicate that some brain structures, such as the frontal lobes of the cerebral cortex--which play a important role in a person's ability to shift attention flexibly, inhibit responses, and solve problems strategically with a goal in mind---tend to be smaller in people with ADHD. Symptoms of ADHD, particularly inattention and hyperactivity, have been found to be associated with abnormally low levels of dopamine, a neurotransmitter that is essential for normal muscle control. Substance use during pregnancy, prematurity, lead exposure in early childhood, and brain injury are associated with increased risk for ADHD.

Environmental influences are also thought to be important in ADHD, and effective psychosocial approaches to treatment focus on altering environmental characteristics and contingencies, for example, increasing structure, reducing distractions, and implementing clear and consistent rules and consequences for behavior. Chaotic environments, such as those experienced by children in high-conflict or abusive families or by children whose parents have poor parenting skills, tend to exacerbate symptoms of ADHD as well as its associated impairments. However, they do not cause ADHD.

Certain theories regarding other potential causes of ADHD--for example, dietary factors (e.g., food allergies, sensitivities to food additives, sugar consumption), environmental allergies or sensitivities--have garnered much attention in the popular media. However, they have received little or no research support to date.