Attention deficit hyperactivity disorder (ADHD) affects children and teens and can continue into adulthood. ADHD is the most commonly diagnosed mental disorder of children. Children with ADHD may be hyperactive and unable control their impulses. Or they may have trouble paying attention. These behaviors interfere with school and home life. It’s more common in boys than in girls. It’s usually discovered during the early school years, when a child begins to have problems paying attention. Adults with ADHD may have trouble managing time, being organized, setting goals, and holding down a job. They may also have problems with relationships, self-esteem, and addiction. Causes of ADHD The cause of ADHD isn’t known. Researchers say several things may lead to it, including: Heredity. ADHD tends to run in families. Chemical imbalance. Brain chemicals in people with ADHD may be out of balance. Brain changes. Areas of the brain that control attention are less active in children with ADHD. Poor nutrition, infections, smoking, drinking, and substance abuse during pregnancy. These things can affect a baby’s brain development. Toxins, such as lead. They may affect a child's brain development. A brain injury or a brain disorder. Damage to the front of the brain, called the frontal lobe, can cause problems with controlling impulses and emotions.