Chronic ADHD is characterized by recurrent episodes of hyperactivity, impulsivity, and inattention. ADHD commonly persists throughout adulthood, starting in infancy. Up to two out of every three children diagnosed with ADHD go on to experience symptoms as adults.

While each individual with ADHD experiences symptoms differently, there are three main forms of ADHD. The signs of impulsivity, hyperactivity, and inattention distinguish each one. The type is typically referred to as mostly inattentive when the primary symptoms are disorganization, distraction, and inattention. The predominantly hyperactive/impulsive type exhibits indications of hyperactivity and maybe impulsiveness, which seem to lessen with maturity. The third form, known as the mixed type, has certain symptoms with the other two.

Children with ADHD might struggle to make and maintain friends, as well as to perform well at home and at school. ADHD may impede social and emotional growth, employment, and education if addressed.