What causes it?

There is no single 'cause' of ADHD, and no simple test for the condition. The exact mechanisms involved in development of ADHD are not fully understood, but there is a lot of evidence for a biological cause, and for several key contributing factors. The importance of these different factors probably varies from child to child.

Known factors are:

Genes and inheritance

• It is suggested that there are both genetic and environmental factors implicated in whether or not a child will develop ADHD; further work is needed to establish the precise nature of current findings.⁷

Brain processes

Studies using brain scans have revealed differences in the development, structure and functioning of the brain in people with and without ADHD.

• Changes involving some of the chemical messengers in the brain - dopamine, serotonin and norepinephrine - are thought to be involved in ADHD.⁷

Environmental factors that may contribute¹⁰

• Excessive alcohol consumption or smoking during pregnancy
• Low birth weight
• Brain injury during pregnancy