What causes ADHD?

Studies have shown that many genes are linked to ADHD, and each gene plays a small role in the disorder. This disorder is complex and there is no testing available just yet to determine and diagnose it. As for the non-genetic factors that could contribute to a child's risk for developing ADHD include - Smoking or drinking during pregnancy. - Birth complications or very low birth weight - Exposure to lead or other toxic substances - Extreme neglect, abuse, or social deprivation. - Food additives like artificial coloring, which might make hyperactivity worse. http://www.nimh.nih.gov/health/publications/attention-deficit-hyperactivity-disorder-easy-to-read/index.shtml