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What Is ADHD? What Are Causes And Symptoms of ADHD?

What is ADHD?

Attention deficit/hyperactivity disorder (ADHD) is a developmental disorder characterized by distractibility, hyperactivity, impulsive behaviors, and the inability to remain focused on tasks or activities.

ADHD was first described in 1845. The estimated prevalence of ADHD, also known as hyperkinetic disorder (HKD) outside of the United States, is 8% to 10% of children. Although difficult to assess in infancy and toddlerhood, signs of ADHD may begin to appear as early as age two or three, but the symptom picture changes as adolescence approaches.Many symptoms, particularly hyperactivity, diminish in early adulthood; however, up to 70% of individuals with ADHD experience persistent impulsivity and problems focusing attention throughout their adult lives. Inattention is the most frequent persistent symptom in adults with ADHD.

what is ADHD

Clinical observation and epidemiological surveys typically report a greater incidence in boys than girls (approximately 2:1). More than 5.5 million children in the United States take amphetamine-type drugs for ADHD each day. Onset is usually by the age of three, although the diagnosis is often not made until later, when the child is in school.

The characteristics of ADHD in order of frequency are: (1) hyperactivity, (2) emotional instability (mood swings, outbursts, etc.), (3) clumsiness, (4) disorders of attention (short attention span, distractibility,failure to finish things off, not listening, poor concentration), (5) impulsiveness (action before thought, abrupt shifts in activity, poor organizing, jumping up in class), (6) disorders of memory and thinking, (7) specific learning disabilities, (8) disorders of speech and hearing, and (9) various neurological signs and brainwave pattern irregularities.

These characteristics are frequently associated with difficulties in school, both in learning and in behavior. If not intensively managed, a child with ADHD will be likely to experience academic impairment, increasedrisk of injuries, and problems with self-esteem and socialization. Later in adolescence and adulthood, those with ADHD have a high risk of experiencing depression or anxiety, substance abuse and addictions, traffic accidents, financial problems, vocational underachievement, and social problems. Nevertheless, ADHD is a condition that can be transcended—many people with ADHD have achieved a high level of personal success.

What causes ADHD?

The causes of ADHD are thought to be an interaction of environment and genes. Heredity plays a majorrole in the development of ADHD. A number of genes considered to confer susceptibility to ADHD have been identified, and some researchers have suggested that ADHD may arise from several different combinations of these susceptibility genes and environmental factors. These genes primarily involve the signaling proteins active in the brain’s dopamine (a nerve-signaling molecule) pathways, supporting the prevailing theory that the signaling of dopamine and other neurotransmitters is responsible for the symptoms of the disorder. Brain imaging results also support this idea. These studies have identified distinct differences in dopamine processing and uptake in the brains of people with ADHD compared to those of people without the disorder. Some researchers see a link between ADHD and obsessive-compulsive disorder (OCD) in heredity studies of families, and children with an ADHD parent or sibling are more likely to develop the disorder themselves. Studies of identical twins point to a heritability rate as high as 91%.

what causes ADHD

Some environmental factors have been strongly linked to ADHD. Studies have found that maternalsmoking during pregnancy can increase a child’s overall risk of ADHD by two-and-a-half times, and if the child is a girl, the risk can be as much as 4.6 times higher. Low birth weight also has been identified as a risk factor, and lead exposure has been linked to ADHD; lead levels above a predetermined cutoff in onestudy were linked to a fourfold increase in the risk of having ADHD. Traumatic brain injury or neurological disorders may also trigger ADHD symptoms.

Symptoms of ADHD

The diagnosis of ADHD requires the presence of at least six of the following symptoms of inattention, or six or more symptoms of hyperactivity and impulsivity combined:


  • fails to pay close attention to detail or makes careless mistakes in schoolwork or other activities 
  • has difficulty sustaining attention in tasks or activities 
  • does not appear to listen when spoken to 
  • does not follow through on instructions and does not finish tasks 
  • has difficulty organizing tasks and activities 
  • avoids or dislikes tasks that require sustained mental effort (e.g., homework) 
  • is easily distracted 
  • is forgetful in daily activities


  • fidgets with hands or feet or squirms in seat 
  • does not remain seated when expected to 
  • runs or climbs excessively when inappropriate (in adolescents and adults, feelings of restlessness) 
  • has difficulty playing quietly  is constantly on the move 
  • talks excessively


  • blurts out answers before the question has been completed 
  • has difficulty waiting turns 
  • interrupts and/or intrudes on others

Further criteria to establish a diagnosis also require that some symptoms develop before age seven, and that they significantly impair functioning in two or more settings (e.g., home and school) for a period of at least six months.

ADHD symptoms

Many individuals with ADHD have symptoms from all three of the above categories. Some children, however, have behavior patterns in which inattention dominates, or hyperactivity and impulsivity dominate. For this reason, ADHD can be further categorized, or subdivided, into three subtypes. Children who have at least six symptoms from both of the inattention and hyperactivity–impulsivity categories may be diagnosed with ADHD, combined type. Children who meet the symptom criteria for inattention, but not for hyperactivity–impulsivity, are diagnosed with attention deficit/hyperactivity disorder, predominantly inattentive type, commonly called attention deficit disorder (ADD). Children with predominantly attentive type may go undiagnosed until negative academic consequences arise; children who daydream are muchless noticeable than children who are in constant, impulsive motion. Children who experience more symptoms from the hyperactivity and impulsivity categories, but fewer than six symptoms of inattention may be diagnosed with ADHD, predominantly hyperactive–impulsive type.

Diagnosis of ADHD

The first step in determining if a child has ADHD is to consult with a pediatrician. The pediatrician can make an initial evaluation of the child’s developmental maturity compared to other children in the same age group, using guidelines for the diagnosis and evaluation of ADHD provided by the American Academy of Pediatrics. The physician should also perform a comprehensive physical examination to rule out any organic causes of ADHD symptoms, such as an overactive thyroid or vision or hearing problems.

If no organic problem can be found, a psychologist, psychiatrist, neurologist/pediatric neurologist, neuropsychologist, developmental pediatrician, or learning specialist is typically consulted to perform a comprehensive ADHD assessment. A complete medical, family, social, psychiatric, and educational history is compiled from existing medical and school records and from interviews with parents and teachers. Interviews may also be conducted with the children, depending on their age. Along with these interviews, several clinical questionnaires may also be used, such as the Conners’ Rating Scales (Teacher’s Questionnaire and Parent’s Questionnaire), Child Behavior Checklist (CBCL), and the Achenbach Child Behavior Checklist. These inventories provide valuable information on the child’s behavior in different settings and situations. In addition, the Wender Utah Rating Scale has been adapted for use in diagnosing ADHD in adults, as has the Conners’ Adult ADHD rating scale.

It is important to note that mental disorders such as depression and anxiety disorder can cause symptoms similar to ADHD: Depression can cause attention problems, and anxiety can cause symptoms similar to hyperactivity. A complete and comprehensive psychological assessment is critical to differentiate ADHD from other possible mood and behavioral disorders. Bipolar disorder, for example, may be misdiagnosed as ADHD.

Federal law requires a public school to assess children when ADHD is suspected and there are observable effects on their schoolwork and interactions with peers. A pediatrician can also provide a referral to a psychologist or pediatric specialist for ADHD assessment. Parents should check with their insuranceplans to see if these services are covered if they choose to pursue a private evaluation.

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