Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by executive dysfunction occasioning symptoms of inattention, hyperactivity, impulsivity and emotional dysregulation that are excessive and pervasive, impairing in multiple contexts, and otherwise age-inappropriate.

ADHD symptoms arise from executive dysfunction, and emotional dysregulation is often considered a core symptom In children, problems paying attention may result in poor school performance. ADHD is associated with other neurodevelopmental and mental disorders as well as some non-psychiatric disorders, which can cause additional impairment, especially in modern society. Although people with ADHD struggle to sustain attention on tasks that entail delayed rewards or consequences, they are often able to maintain an unusually prolonged and intense level of attention for tasks they do find interesting or rewarding; this is known as hyperfocus.

The precise causes of ADHD are unknown in the majority of cases.For most people with ADHD, many genetic and environmental risk factors accumulate to cause the disorder. The environmental risks for ADHD most often exert their influence in the early prenatal period. In some cases a single event might cause ADHD such as traumatic brain injury, exposure to biohazards during pregnancy, a major genetic mutation or extreme nutritional deprivation early in life. Later in life, there is no biologically distinct adult onset ADHD except for when ADHD occurs after traumatic brain injury

Genetic factors play an important role; ADHD tends to run in families and has a heritability rate of 74%. Toxins and infections during pregnancy as well as brain damage may be environmental risks.

It affects about 5–7% of children when diagnosed via the DSM-IV criteria and 1–2% when diagnosed via the ICD-10 criteria.Rates are similar between countries and differences in rates depend mostly on how it is diagnosed.ADHD is diagnosed approximately twice as often in boys as in girls,and 1.6 times more often in men than in women, although the disorder is overlooked in girls or diagnosed in later life because their symptoms sometimes differ from diagnostic criteria. About 30–50% of people diagnosed in childhood continue to have ADHD in adulthood, with 2.58% of adults estimated to have ADHD which began in childhood. In adults, hyperactivity is usually replaced by inner restlessness, and adults often develop coping skills to compensate for their impairments. The condition can be difficult to tell apart from other conditions, as well as from high levels of activity within the range of normal behavior. ADHD has a negative impact on patient health-related quality of life that may be further exacerbated by, or may increase the risk of, other psychiatric conditions such as anxiety and depression

ADHD management recommendations vary and usually involve some combination of medications, counseling, and lifestyle changes.The British guideline emphasizes environmental modifications and education about ADHD for individuals and carers as the first response. If symptoms persist, parent-training, medication, or psychotherapy (especially cognitive behavioral therapy) can be recommended based on age. Canadian and American guidelines recommend medications and behavioral therapy together, except in preschool-aged children for whom the first-line treatment is behavioral therapy alone. Medications are the most effective pharmaceutical treatment, although there may be side effects and any improvements will be reverted if medication is ceased

ADHD, its diagnosis, and its treatment have been considered controversial since the 1970s. These controversies have involved doctors, teachers, policymakers, parents, and the media. Topics have included causes of ADHD and the use of stimulant medications in its treatment. ADHD is now a well-validated clinical diagnosis in children and adults, and the debate in the scientific community mainly centers on how it is diagnosed and treated. ADHD was officially known as attention deficit disorder (ADD) from 1980 to 1987; prior to the 1980s, it was known as hyperkinetic reaction of childhood. Symptoms similar to those of ADHD have been described in medical literature dating back to the 18th century.

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 signs and 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. In June 2021, Neuroscience Biobehavioral Reviews published a systematic review of 82 studies that all confirmed or implied elevated accident-proneness in ADHD patients and whose data suggested that the type of accidents or injuries and overall risk changes in ADHD patients over the lifespan. In January 2014, Accident Analysis Prevention published a meta-analysis of 16 studies examining the relative risk of traffic collisions for drivers with ADHD, finding an overall relative risk estimate of 1.36 without controlling for exposure, a relative risk estimate of 1.29 when controlling for publication bias, a relative risk estimate of 1.23 when controlling for exposure, and a relative risk estimate of 1.86 for ADHD drivers with oppositional defiant disorder and/or conduct disorder comorbidities.

According to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and its text revision, symptoms must be present for six months or more to a degree that is much greater than others of the same age.] This requires at least six symptoms of either inattention or hyperactivity/impulsivity for those under 17 and at least five symptoms for those 17 years or older. The symptoms must be present in at least two settings (e.g., social, school, work, or home), and must directly interfere with or reduce quality of functioning.Additionally, several symptoms must have been present before age twelve.]

Presentations

ADHD is divided into three primary presentations predominantly inattentive (ADHD-PI or ADHD-I)

• predominantly hyperactive-impulsive (ADHD-PH or ADHD-HI)
• combined presentation (ADHD-C).

The table "Symptoms" lists the symptoms for ADHD-I and ADHD-HI from two major classification systems. Symptoms which can be better explained by another psychiatric or medical condition which an individual has are not considered to be a symptom of ADHD for that person. In DSM-5, subtypes were discarded and reclassified as presentations of the disorder that change over time.