What actually causes ADHD—like, why does it develop in some people?

ADHD develops from a combination of genetics and brain development. It is highly heritable, meaning it runs strongly in families, but it is not caused by a single gene. Many genes influence dopamine regulation, brain connectivity, and executive function. Brain imaging shows differences in how attention and regulation networks develop and communicate, especially in the prefrontal cortex. Environment does not cause ADHD, but it influences how it shows up. Stress, sleep, trauma, and support can worsen or buffer symptoms. Families often cluster with ADHD because genetics concentrate, not because of parenting style.