Signs and symptoms

Inattention, hyperactivity (restlessness in adults), disruptive behavior, and impulsivity are common in ADHD. Academic difficulties are frequent as are problems with relationships. The symptoms can be difficult to define as it is hard to draw a line at where normal levels of inattention, hyperactivity, and impulsivity end and significant levels requiring interventions begin.

According to the DSM-5, symptoms must be present for six months or more to a degree that is much greater than others of the same age and they must cause significant problems functioning in at least two settings (e.g., social, school/work, or home). The full criteria must have been met prior to age 12 in order to receive a diagnosis of ADHD.
ADHD is divided into three subtypes: predominantly inattentive, predominantly hyperactive-impulsive, and combined type.

An individual with ADHD inattentive type has most or all of following symptoms, excluding situations where these symptoms are better explained by another psychiatric or medical condition:

• Be easily distracted, miss details, forget things, and frequently switch from one activity to another
• Have difficulty maintaining focus on one task
• Become bored with a task after only a few minutes, unless doing something enjoyable
• Have difficulty focusing attention on organizing and completing a task or learning something new
• Have trouble completing or turning in homework assignments, often losing things (e.g., pencils, toys, assignments) needed to complete tasks or activities
• Not seem to listen when spoken to
• Daydream, become easily confused, and move slowly
• Have difficulty processing information as quickly and accurately as others
• Struggle to follow instructions
• Have trouble understanding minute details

An individual with ADHD hyperactive/impulsive type has most or all of the following symptoms, excluding situations where these symptoms are better explained by another psychiatric or medical condition: 

• Fidget and squirm in their seats
• Talk nonstop
• Dash around, touching or playing with anything and everything in sight
• Have trouble sitting still during dinner, school, doing homework, and story time
• Be constantly in motion
• Have difficulty doing quiet tasks or activities
• Be very impatient
• Blurt out inappropriate comments, show their emotions without restraint, and act without regard for consequences
• Have difficulty waiting for things they want or waiting their turns in games
• Often interrupt conversations or others' activities

Symptoms of hyperactivity tend to go away with age and turn into "inner restlessness" in teens and adults with ADHD.

People with ADHD are more likely to have problems with social skills, such as social interaction and forming and maintaining friendships. This is true for all subtypes. About half of children and adolescents with ADHD experience social rejection by their peers compared to 10–15% of non-ADHD children and adolescents. People with attention deficits are prone to having difficulty processing verbal and nonverbal language which can negatively affect social interaction. They also may drift off during conversations, and miss social cues.

Difficulties managing anger are more common in children with ADHD as are poor handwriting and delays in speech, language and motor development. Although it causes significant impairment, particularly in modern society, many children with ADHD have a good attention span for tasks they find interesting.