ADHD Essentials

What Is ADHD? Meaning, Symptoms & Tests

The meaning of ADHD is complex. It’s a misunderstood neurological disorder that impacts the parts of the brain that help us plan, focus on, and execute tasks. ADHD symptoms vary by sub-type — inattentive, hyperactive, or combined — and are often more difficult to diagnose in girls and adults. Here, we review the symptoms, causes, types, and tests associated with attention deficit hyperactivity disorder.

What Is ADHD?

ADHD stands for attention deficit hyperactivity disorder, a complex brain disorder that impacts approximately 11% of children and almost 5% of adults in the U.S.1 ADHD is a developmental impairment of the brain’s executive functions. People with ADHD have trouble with impulse-control, focusing, and organization.

Neuroscience, brain imaging, and clinical research tell us a few important things: ADHD is not a behavior disorder. ADHD is not a mental illness. ADHD is not a specific learning disability.

ADHD is, instead, a developmental impairment of the brain’s self-management system. Common ADHD symptoms include:

  • inattention
  • lack of focus
  • poor time management
  • weak impulse control
  • exaggerated emotions
  • hyperfocus
  • hyperactivity
  • and executive dysfunction

Many patients and clinicians describe ADHD as an iceberg, where most symptoms lay hiding under the surface — out of sight but ever present.

What Is the Definition of ADHD?

“Attention deficit” is, some experts assert, a misleading name. “Attention deregulation” might be a more accurate description since most people with ADHD have more than enough attention — they just can’t harness it in the right direction at the right time with any consistency. And so individuals with ADHD hyperfocus and lose track of time, or misplace their keys, or blurt out an unrelated thought when their focus breaks free from its chains.

What is ADHD Caused By?

The causes of ADHD remain somewhat unclear. Is ADHD genetic? Research suggests that genetics and heredity play a large part in determining who gets attention deficit hyperactivity disorder.2 However, scientists are still investigating whether certain genes, especially ones linked to the neurotransmitter dopamine, play a defined role in developing ADHD. Additional research suggests that exposure to toxins and chemicals may increase a child’s risk of having ADHD.3

ADHD is not caused by bad parenting, too much sugar, or too many video games. ADHD is a brain-based, biological disorder. Brain imaging studies and other research show many physiological differences in the brains of individuals with ADHD.4

What Are the 3 Subtypes of ADHD?

The Diagnostic and Statistical Manual of Mental Disorders (DSM)5 previously identified three types of ADHD:

  • Primarily hyperactive-impulsive type
  • Primarily inattentive type (formerly called ADD)
  • Primarily combined type

People with hyperactive-impulsive subtype of ADHD act “as if driven by a motor” with little impulse control — moving, squirming, and talking at even the most inappropriate times. They are impulsive, impatient, and interrupt others.

People with the inattentive subtype of ADHD are easily distracted and forgetful. They may be daydreamers who lose track of homework, cell phones, and conversations with regularity.

Individuals with combined-type ADHD display a mixture of all the symptoms outlined above.

These subtypes are now considered “presentations” in the most recent version of the DSM, the DSM-V. Researchers determined that people often move from one subtype to another. For example, a child may present as primarily hyperactive-impulsive in preschool, and  lose much of the hyperarousal in adolescence to fit the primarily inattentive presentation. In college and adulthood, the same individual may transition to combined presentation.

The subtypes were primarily based on overt behavioral symptoms, and ignored less visible symptoms like emotional dysregulation, cognitive patterns, and sleep difficulties. Behavioral symptoms imperfectly capture the defining features of ADHD. Non-behavioral characteristics are increasingly recognized in research and diagnosis.

What Are the Symptoms of ADHD?

The symptoms of ADHD are spelled out in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V), which lists nine symptoms that suggest ADHD–Primarily Inattentive and nine that suggest ADHD–Primarily Hyperactive/Impulsive. A child may be diagnosed with ADHD only if he or she exhibits at least six of nine symptoms from one of the lists below, and if the symptoms have been noticeable for at least six months in two or more settings — for example, at home and at school. What’s more, the symptoms must interfere with the child’s functioning or development, and at least some of the symptoms must have been apparent before age 126. Older teens and adults may need to consistently demonstrate just five of these symptoms in multiple settings.

What Are the 9 Symptoms of ADHD – Primarily Inattentive Type?

  • Often fails to give close attention to details or makes careless mistakes in schoolwork, at work, or during other activities (e.g., overlooks or misses details, work is inaccurate).
  • Often has difficulty sustaining attention in tasks or play activities (e.g., has difficulty remaining focused during lectures, conversations, or lengthy reading).
  • Often does not seem to listen when spoken to directly (e.g., mind seems elsewhere, even in the absence of any obvious distraction).
  • Often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace (e.g., starts tasks but quickly loses focus and is easily sidetracked).
  • Often has difficulty organizing tasks and activities (e.g., difficulty managing sequential tasks; difficulty keeping materials and belongings in order; messy, disorganized work; has poor time management; fails to meet deadlines).
  • Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (e.g., schoolwork or homework; for older adolescents and adults, preparing reports, completing forms, reviewing lengthy papers).
  • Often loses things necessary for tasks or activities (e.g., school materials, pencils, books, tools, wallets, keys, paperwork, eyeglasses, mobile telephones).
  • Is often easily distracted by extraneous stimuli (for older adolescents and adults, may include unrelated thoughts).
  • Is often forgetful in daily activities (e.g., doing chores, running errands; for older adolescents and adults, returning calls, paying bills, keeping appointments).

[Self-Test: Symptoms of Inattentive ADHD in Children]
[Self-Test: Symptoms of Inattentive ADHD in Adults]

What Are the 9 Symptoms of ADHD – Primarily Hyperactive-Impulsive Type?

  • Often fidgets with or taps hands or feet or squirms in seat.
  • Often leaves seat in situations when remaining seated is expected (e.g., leaves his or her place in the classroom, in the office or other workplace, or in other situations that require remaining in place).
  • Often runs about or climbs in situations where it is inappropriate. (Note: In adolescents or adults, may be limited to feeling restless.)
  • Often unable to play or engage in leisure activities quietly.
  • Is often “on the go,” acting as if “driven by a motor” (e.g., is unable to be or uncomfortable being still for extended time, as in restaurants, meetings; may be experienced by others as being restless or difficult to keep up with).
  • Often talks excessively.
  • Often blurts out an answer before a question has been completed (e.g., completes people’s sentences; cannot wait for turn in conversation).
  • Often has difficulty waiting his or her turn (e.g., while waiting in line).
  • Often interrupts or intrudes on others (e.g., butts into conversations, games, or activities; may start using other people’s things without asking or receiving permission; for adolescents and adults, may intrude into or take over what others are doing).”

[Self-Test: Symptoms of Hyperactive & Impulsive ADHD in Children]
[Self-Test: Symptoms of Hyperactive & Impulsive ADHD in Adults]

1 “Data & Statistics.” Centers for Disease Control and Prevention. Ed. Center for Disease Control. Centers for Disease Control and Prevention, 14 Feb. 2017. Web. 14 Mar. 2017.
2 Thapar, Anita, and Evangelia Stergiakouli. “An Overview on the Genetics of ADHD.” Xin li xue bao. Acta psychologica Sinica (Aug. 2008) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2854824/
3 Philip J. Landrigan, Jordan Slutsky. Are Learning Disabilities Linked to Environmental Toxins? Learning Disabilities Worldwide. https://www.ldworldwide.org/environmental-toxins
4 Dovey, Dana. “Doctors May Soon Be Able To Diagnose ADHD With An MRI Scan.” Medical Daily. IBT Media Inc., 30 Apr. 2014. Web. 14 Mar. 2017.
5 Association, American Psychiatric, ed. Diagnostic and Statistical Manual of Mental Disorders: DSM-5. Washington: American Psychiatric, 2014.
6 Association, American Psychiatric, ed. Diagnostic and Statistical Manual of Mental Disorders: DSM-5. Washington: American Psychiatric, 2014.

Updated on November 8, 2019

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  1. As someone with ADHD, this description is spot-on (at least for my case). It’s almost a constant feeling that you’re missing out on something. Like if you don’t respond to that text immediately or address a separate thought immediately you’ll never get to it.

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