Attention-Deficit/Hyperactivity Disorder - Definition
Attention-deficit/hyperactivity disorder (ADHD) is a condition that shows up most commonly in boys and girls after puberty begins. Puberty is the period in life when a person's sex hormones become active. ADHD is characterized by an inability to concentrate on tasks, hyperactivity (an abnormally high level of physical activity), and unpredictable behavior. ADHD is known as hyperkinetic disorder (HKD) outside of the United States.
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