Attention deficit hyperactivity disorder (ADHD) is the technical term that describes a neurobiological disorder with genetic causes that appears in childhood and often accompanies the individual throughout his or her life. This disorder is characterized by inattention, hyperactivity and impulsivity, and any of these symptoms may predominate. It is considered the most common developmental disorder in childhood and adolescence, affecting approximately 3% to 7% of these populations worldwide, and commonly extending into adulthood(9). The media has overly publicized ADHD as the main culprit and, in some cases, the sole cause of school difficulties in children in general. Because of this, we must be cautious and careful with this diagnosis, which in some cases is overestimated and has been used as an escape valve by families, schools and professionals. To date, the diagnosis is based exclusively on the history of behavior, and there are no complementary tests that can validate it. Furthermore, its neurobiological basis is still poorly understood. In this review, we will write about some relevant aspects of ADHD, trying to emphasize the important aspects for the general practitioner, who is usually the first health professional to come across patients with this disorder, which is so much talked about these days. EPIDEMIOLOGY ADHD is the most common disorder in children and adolescents referred to specialized neuropediatric and child psychiatry services. The data remain imprecise and are highly influenced by the criteria used for diagnosis. It is believed to occur in approximately 5% of children(7). In adolescents and adults, there is still little data regarding the percentage of the population affected, but it is common sense that both groups can develop the disorder. Males are more affected than females, in a proportion that varies from 4:1 to 10:1, depending on the criteria used. In females, there is a higher incidence of the inattentive form (which we will discuss later). BRIEF HISTORY The first description of ADHD dates back to 1902, when an English physician, G. Still, described a set of behavioral changes in children. According to him, these changes could not be explained by environmental failures, but were due to some unknown biological process. The author called this set of symptoms a deficit of moral control . In the 1930s, Strauss et al. described hyperactivity, distractibility, emotional lability, and perseveration in a group of survivors of encephalitis lethargica. These behaviors were considered evidence of the presence of brain damage, and it was suggested that children who demonstrated these behaviors had brain damage even when there was no known damage. Since the first description of this attention disorder in the early 20th century, this clinical condition has received several names over time. It has been called minimal brain damage, minimal brain dysfunction, hyperactive child syndrome, primary attention disorder, and attention deficit disorder with or without hyperactivity. With the publication of the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) by the American Academy of Psychiatry (1980), the current nomenclature began to be used. Since the beginning of its observation until today, studies on attention deficit disorder have referred to children in their vast majority. This is because the diagnostic criteria for attention deficit disorder, according to the DSM-IV, refer to the most commonly observed characteristics in children. For this reason, many adults diagnosed with attention deficit disorder end up not meeting these criteria (Petot, 2003). Finally, it was believed that the symptoms of attention deficit disorder disappeared spontaneously in adolescence or, at most, in early adulthood. However, some authors report that the disorder persists in approximately 50% to 70% of cases in adulthood, although the clinical picture undergoes some modifications over time(12). DIAGNOSIS The diagnosis must be made by ruling out other pathologies or socio-environmental problems that could potentially be the origin of the symptoms. In addition, the symptoms must necessarily bring some type of difficulty or impediment to performing tasks. Neuropsychological tests (e.g., the Wisconsin Card-Sorting Test or the Stroop Test), as well as neuroimaging tests (CT scan, MRI or brain SPECT) and genetic testing, are still in the research setting and should not be part of the diagnostic routine. It is important to remember that, in the physical examination, the formal neurological examination is absolutely normal, with only alterations in the motor persistence tests, which may indicate some degree of neurological immaturity (motor persistence tests are not part of the formal neurological evaluation, and in the developmental neurological examination tests, abnormalities in other areas, such as balance, fine motor coordination, etc., may be present in children with ADHD). The diagnosis is based solely on the clinical criteria that we will present below. DIAGNOSTIC CRITERIA FOR ATTENTION DEFICIT/HYPERACTIVITY DISORDER (DSM-IV)

• Presence of six (or more) of the following symptoms of inattention that persist for at least six months, to a degree inconsistent with developmental level:

– inattention: 1. often fails to give close attention to details or makes gross errors in schoolwork, homework, etc.; 2. often has difficulty sustaining attention in tasks or play activities; 3. often appears not to listen when spoken to directly; 4. often fails to follow instructions completely or to finish schoolwork, household chores, or homework (not due to a negative attitude or failure to understand instructions); 5. has difficulty organizing tasks and activities; 6. often avoids, dislikes, or is reluctant to engage in activities that require sustained mental effort (such as schoolwork or housework); 7. often loses things necessary for activities or work (e.g., toys, schoolwork, pencils, books, tools, personal belongings); 8. is easily distracted by external stimuli; 9. often forgets about daily activities.

• Hyperactivity/impulsivity defined by the presence of six of the nine criteria below, of which six relate to hyperactivity and three to impulsivity:

– hyperactivity: 1. often fidgets with hands and feet, or fidgets constantly when seated; 2. often leaves seat in class or other situations when remaining seated is expected; 3. runs around or climbs on things in situations where this is inappropriate (in adolescents or adults, this may be limited to a subjective feeling of restlessness); 4. often has difficulty playing or engaging in leisure activities in a calm manner; 5. is often ready to take off, or acts as if on a motor; 6. talks excessively; – impulsivity: 7. often answers abruptly before a question has been fully asked; 8. has difficulty waiting for his or her turn; 9. often intrudes or interrupts others (e.g., butting into conversations or games).

• Some symptoms of hyperactivity/impulsivity or inattention that cause impairment were present before age 7 years.
• Some impairment caused by symptoms is present in two or more settings (e.g., at school or work and at home).
• There must be clear evidence of clinically significant impairment in social, academic, or occupational functioning.
• The symptoms do not occur exclusively during the course of a pervasive developmental disorder, schizophrenia, or other psychotic disorder and are not better explained by another mental disorder (e.g., mood, anxiety, dissociative, or personality disorder).

It is important to remember that other mental disorders can also present agitation as a symptom, including autism spectrum disorder, mental retardation, conduct disorder, and oppositional defiant disorder. Therefore, detailing the presence of other symptoms inherent to this group of disorders in the history is essential both to exclude diagnoses and to evaluate other associated disorders. Because of this, we must always keep in mind the main differential diagnoses:

• anxiety (which may accompany ADHD as a secondary aspect);
• primary depressive disorder (many children with ADHD have depression secondary to frustration due to their learning failure and subsequent low self-esteem);
• conduct disorders (usually associated with ADHD);
• learning disorders of various kinds;
• sensory impairment, particularly hearing;
• typical absence (petit mal);
• side effect of medications (antipsychotics, anticonvulsants, which can cause psychomotor agitation and attention problems).

EVOLUTION The course of ADHD is highly variable. Symptoms may persist into adolescence and adulthood, with a decrease in puberty, or hyperactivity may disappear, with a persistent reduced attention span and impulse control problems. Hyperactivity is usually the first symptom to show remission, and inattention is the last. Remission usually occurs between 12 and 20 years of age. The existence of the adult form of ADHD was only officially recognized in 1980 by the American Psychiatric Association. Since then, numerous studies have demonstrated the presence of ADHD in adults. It took a long time for it to be widely publicized in the medical community, and even today, it is observed that this diagnosis is rarely made, with the mistaken stereotype of ADHD persisting: a disorder affecting hyperactive boys who perform poorly at school. ADHD also occurs in girls, but it also occurs without hyperactivity and is not always associated with poor school performance. Many doctors are unaware of the existence of ADHD in adults, and when these patients come to them, they tend to treat them as if they had other problems (personality problems, for example). When there is actually another associated problem (depression, anxiety or drugs), the doctor only diagnoses the latter, and not ADHD. Currently, it is believed that around 60% of children with ADHD will enter adulthood with some of the symptoms (both inattention and hyperactivity/impulsivity), but in fewer numbers and intensity than they had when they were children or adolescents. In many cases, ADHD symptoms will be associated with various difficulties in social, family and professional life, requiring treatment. In other individuals, however, there may be symptoms that do not cause significant problems in their lives and, therefore, do not require treatment. It is always important to determine whether ADHD symptoms are responsible for the problems that the individual presents (they may have several problems that are not related to ADHD). There are also cases in which the symptoms have improved significantly and almost disappeared, but the problems they caused throughout life are still present; these cases also require treatment. In order to diagnose ADHD in adults, it is essential to demonstrate that the disorder has been present since childhood. This can be difficult in some situations, because the individual may not remember their childhood and their parents may be deceased or too old to report the condition to the doctor. The symptoms listed in the DSM-IV are the same for children, adolescents, and adults. In general, adults have fewer symptoms, although they had the necessary amount for a correct diagnosis when they were younger. In other words, adults with ADHD have always been inattentive, since they were little, as well as restless and impulsive. Adults with ADHD often have difficulty organizing and planning their daily activities. For example, it can be difficult for a person with ADHD to determine what is most important among the many things they have to do, and to choose what to do first and what to put off until later. As a result, people with ADHD can become anxious because when they feel overwhelmed (and it is very common for them to be overwhelmed frequently, since they have so many different commitments), they do not know where to start and are afraid that they will not be able to do everything. Individuals with ADHD end up leaving work half-done, stopping halfway through what they are doing and starting something else, only returning to the previous task much later than intended or even forgetting about it. Thus, individuals with ADHD have difficulty performing tasks alone, especially when there are many, and they constantly need to be reminded by others about what they have to do. All of this can cause problems in college, at work, or in relationships with other people. CO-MORBIDITY There is growing evidence, however, that many conditions co-exist with ADHD, and each one modifies the overall clinical presentation and response to treatment. These conditions should be considered simultaneously in order to broaden our knowledge and maximize treatment. Depressed patients, for example, demonstrate decreased concentration, and individuals with bipolar disorder often manifest psychomotor agitation and a high degree of distractibility. It can be difficult to differentiate these symptoms from the cardinal symptoms of ADHD. Long-term follow-up studies have shown that individuals with ADHD and comorbid disorders have worse prognoses and higher rates of hospitalization than those with ADHD alone. TREATMENT Treatment of ADHD involves a multifaceted approach, encompassing psychosocial and psychopharmacological interventions. Pharmacological Over the past 20 years, more than 500 articles have been published on the use of stimulants, with more than 200 clinical trials demonstrating their efficacy in ADHD. In Brazil, we have methylphenidate (MFD), in doses ranging from 0.3 to 1mg/kg/day, the most widely used, and its longer-lasting presentations. Indications for the use of other medications There are alternative medications to stimulants. They are used in patients who do not benefit from the use of psychostimulants or in those with comorbidities such as anxiety, depression or Tourette’s disorder (tics). Among them we can mention tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs), bupropion, venlafaxine, clonidine and caffeine. Benzodiazepines are contraindicated in the treatment of ADHD, and an agitation effect often occurs in those who use them, called the paradoxical effect. Cognitive-behavioral therapy Psychotherapeutic follow-up aims not only to improve symptoms, but also to prevent or reduce possible resulting emotional and psychological comorbidities. PROGNOSIS Children with ADHD, whose symptoms persist into adolescence, are at high risk for developing conduct disorders, antisocial personality disorders in adulthood and those related to illicit substances. However, an appropriate diagnostic and therapeutic approach can facilitate the development of the ADHD patient, allowing him/her to be adequately integrated into society.