ADHD is now considered to be a neuro genetic disorder, with causes being related to genetics or difficulties in brain development, especially in the fronto-striatal-cerebellar circuits of the brain.

Other causes have been linked to smoking, alcohol use while pregnant, premature birth, pre-pregnancy obesity, high levels of anxiety which increases certain hormones and head trauma but mostly it is 70% genetic and 30% brain trauma.

The resulting symptoms and severity people with ADHD experience, are directly linked to these affected circuits and subsequent pathways, being damaged and/or disrupted. The more severely damaged/disrupted these pathways are, the more severe the symptoms of ADHD appear.