In the absence of finding an exact cause, researchers continue to expand their area of focus beyond genetics and brain structure.
Vaccines have been suspected of being linked to a variety of neurodevelopmental disorders, including ADHD, however studies have not found any evidence of this.
Poor mental health of mothers is another suspected cause of ADHD and studies found that mothers raising children with ADHD were more likely to have a chronic or serious mental health condition.
Mothers smoking during pregnancy has been shown in some studies to have a relationship to the later development of ADHD in their child.
In some studies, injuries during birth have been found to be more common in children with ADHD than in those without the disorder.
Extremely low birth weight has also been found to be associated with ADHD, in some studies.
