While true ADHD is likely caused by hormonal imbalances in the brain, misaligned bones in the spine have two different effects on the nervous system called inhibition and facilitation.  Nerve inhibition can cause muscle weakness and tiredness while nerve facilitation can cause increased sensitivity to environmental stimulus.  When nerves are facilitated, or excited, due to spinal misalignment, they can cause feelings of hyperactivity and restlessness.  Many parents will note that after their child has been adjusted, they seem calmer and tend to sleep better as well.