The exact prevalence of ADHD is unknown; estimates of prevalence have been derived from national surveys, which vary in methodology and age range of young children included in the survey. Estimates of ADHD diagnosis among children in the United States have increased from 6% to 8% in 2000 to 9% to 10% in 2018 [2]. This increase in estimated prevalence of ADHD is due in part to an increased focus on ADHD in younger children and an expanded survey age range to include children as young as 3 years of age. Data from the 2022 National Survey of Children's Health (NSCH) estimated that 7.1 million (11.4%) children 3 to 17 years of age in the United States had ever been diagnosed with ADHD. This includes 274,000 children 3 to 5 years of age, 2.8 million children 6 to 11 years of age, and 4 million adolescents 12 to 17 years of age [147]. Among children with current ADHD, 58.1% had moderate or severe ADHD, 53.6% had received ADHD medication, and 44.4 % had received behavioral treatment for ADHD in the past year.

In children, ADHD is nearly twice as common among boys (15%) as among girls (8%) [2]. In 2016–2018, 13.8% of children 3 to 17 years of age had ever been diagnosed with either ADHD or a learning disability. Non-Hispanic Black children (16.9%) were more likely than non-Hispanic White (14.7%) or Hispanic (11.9%) children to be diagnosed with either condition, although the reason is not clear [3,4]. The prevalence of ADHD among children with family incomes less than 100% of the poverty level was 10% from 1998 to 2009 and 11% for those with family income from 100% to 199% of the poverty level [5].

In children, ADHD can lead to educational difficulties, social difficulties, injuries and accidents, and family problems. Adults with a childhood history of ADHD are more likely to exhibit antisocial and criminal behavior, are more prone to injuries and accidents, and have more health problems than the general population [9]. They also have more employment and marital difficulties and are more likely to have children out of wedlock.

In a community sample of 500 adults with self-reported ADHD and 501 community-based controls, the adults with ADHD were significantly less likely to have graduated from high school (83% vs. 93%), less likely to have obtained a college degree (19% vs. 26%), and less likely to be currently employed (52% vs. 72%). They were more likely to have had job changes (5.4 vs. 3.4 jobs over 10 years), to have been arrested (37% vs. 18% of controls), and to have been divorced (28% vs. 15%). They were also less likely to be satisfied with their professional, family, and social lives [10].

According to the DSM-5-TR criteria for ADHD, one of the following groups of symptoms must be present [11]:

According to the DSM-5-TR criteria for ADHD, one of the following groups of symptoms must be present [11]:

Impairment from the symptoms must be 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. For a diagnosis of ADHD, the symptoms may not occur exclusively during the course of a pervasive developmental disorder, schizophrenia, or other psychotic disorder or be better accounted for by another mental disorder (e.g., mood disorder, anxiety disorder, dissociative disorder, or personality disorder). For individuals (especially adolescents and adults) who have symptoms that no longer meet full criteria, "in partial remission" should be specified. The category unspecified ADHD is for disorders with prominent symptoms of inattention or hyperactivity-impulsivity that do not meet the full criteria for ADHD [11].

There are several changes in symptoms as patients approach adulthood. There appear to be fewer overt symptoms of hyperactivity (e.g., running and climbing, inability to remain seated), but these may be replaced with or confined to fidgetiness, jitteriness, or restlessness. Restlessness may lead to difficulty participating in sedentary activities and even avoiding sedentary occupations. Impulsivity may manifest as a tendency to make decisions without thinking them through [19]. Patients may start on projects without reading or listening to instructions. An adult with ADHD may also have a tendency to speed when driving.

Other typical adult ADHD symptoms include having trouble getting organized, planning ahead, or preparing for events [19]. These patients may appear inefficient, failing to do tasks in the order that makes the most sense. Inattention may manifest as failure to persist in uninteresting tasks or daydreaming instead of concentrating.

The Utah criteria are a set of diagnostic criteria developed specifically to identify adults with ADHD [22]. Although they do not match the DSM-5-TR definition, they may be useful in assessing adult patients. The Utah criteria include [22]:

There have been several genes associated with ADHD, including the dopamine-beta-hydroxylase gene, the dopamine transporter gene, and the dopamine receptor gene [5,24]. However, no gene has been found that reliably predicts ADHD.

Stimulant medications, including amphetamine and methylphenidate, are considered first-line therapy in the treatment of ADHD [5,28]. However, other medications, such as atomoxetine, may be considered [5]. Behavior modification has a role in the overall treatment plan of ADHD, and cognitive-behavioral therapy (CBT) may be helpful for adults, although the evidence for stimulant medications is stronger.

Stimulant medications appear to be effective in treating ADHD, and most children with ADHD will respond to at least one of them [13]. In a review of studies in which subjects underwent a trial of both amphetamine and methylphenidate, about 85% of children responded to one or both of these medications [32]. Forty-one percent responded equally to both classes, and 44% responded preferentially to one or the other. Stimulants are also effective in adults. One systematic review and meta-analysis sought to estimate the comparative efficacy and tolerability of amphetamines (including lisdexamfetamine), methylphenidate, modafinil, atomoxetine, bupropion, clonidine, and guanfacine with each other or placebo for ADHD in children, adolescents, and adults [33]. Efficacy was defined as the change in severity of ADHD core symptoms based on teachers' and clinicians' ratings. For ADHD core symptoms rated by clinicians in children/adolescents closest to 12 weeks, all drugs included in the review were superior to placebo, whereas only methylphenidate was superior to placebo based on teachers' ratings [33]. In adults, amphetamines, methylphenidate, bupropion, and atomoxetine were superior to placebo according to clinicians' ratings. With respect to tolerability, amphetamines were inferior to placebo in all three age groups; guanfacine was inferior to placebo only in children and adolescents; and atomoxetine, methylphenidate, and modafinil were less well tolerated than placebo only in adults. In head-to-head comparisons of the drugs, differences in efficacy, not tolerability, were found (according to clinicians' ratings). Amphetamines were favored over modafinil, atomoxetine, and methylphenidate in all three age groups at 12 weeks [33].

The effect of stimulants is thought to be mediated primarily though their actions on dopamine and norepinephrine transmission. Stimulants have been shown to increase the concentration of these neurotransmitters in the frontal cortex, midbrain, and brain stem, which may explain their effect of increasing attention span and the ability to concentrate [9]. Amphetamines and methylphenidate may differ in specific actions regarding dopamine release [34]. Methylphenidate is to a large extent a norepinephrine and dopamine reuptake inhibitor, while amphetamines promote dopamine and norepinephrine efflux from neurons [35].

Many side effects associated with stimulant use are likely to resolve with time. Side effects that are reported commonly include insomnia, reduced appetite, headaches, stomachaches, and emotional lability [36]. Anorexia often resolves after a few weeks. In children, some height delay has been observed when treatment is initiated, but research shows this growth delay levels off by the end of adolescence [37,38,39].

Stimulant medications are considered safe for use in most children and adults. However, there are areas of concern that should be considered prior to initiating treatment. Although the actual cardiac risk is not known, stimulant medications carry a warning against use in persons with certain cardiac abnormalities, due to sympathomimetic effects [41]. The AAP and the American Heart Association recommend that prior to starting a patient on ADHD medications, patient and family health histories should be obtained and a physical exam should be performed with a focus on cardiovascular disease risk factors [41]. This was a Class I recommendation with level of evidence C, meaning that the recommendation was strong although based primarily on expert consensus, case studies, and/or standard of care. Acquiring an electrocardiogram (ECG) prior to starting treatment was considered reasonable but not mandatory. It was also recommended that the blood pressure and heart rate of the patient on stimulant medication for ADHD be monitored, within 1 to 3 months of starting medication and every 6 to 12 months thereafter (also a IC recommendation) [41]. Later the same year, AAP released a statement supporting the use of careful history and physical exam to assess for cardiac abnormalities [42]. However, this statement noted a lack of evidence to support routine ECGs before prescribing stimulant medications. In 2019, the NICE guidelines amended their recommendation on assessment to indicate that an ECG is not needed before starting stimulants, atomoxetine, or guanfacine if cardiovascular history and examination are normal and the person is not on medication that poses an increased cardiovascular risk [31]. Cardiac risk assessment in adults requires careful consideration in relation to the patient's age and comorbidities when prescribing stimulant medications for ADHD. This risk will be discussed in detail later in this course.

Methylphenidate has been reported to lower seizure threshold in certain children; however, stimulants may be used safely in children who have epilepsy that is well-controlled [43,44,45]. Studies suggest that low doses of methylphenidate may also be safely used in children with difficult-to-treat epilepsy; in these instances, its use positively impacts the patient's quality of life [46,47].

Atomoxetine has been approved by the FDA for the treatment of ADHD in both children and adults; however, it may be less effective than stimulant medications. Atomoxetine is a noradrenergic reuptake inhibitor, and it has several important differences in comparison to stimulants [9,35]. Atomoxetine has different side effects than stimulant medication and is more likely to cause sedation and nausea. The treatment effect may be smaller than that observed with stimulant medications, and its effect may take longer to appear.

Atomoxetine should be discontinued if symptoms of hepatic disease appear. This medication also carries cardiac warnings similar to stimulants. Lastly, atomoxetine carries a black box warning for suicidal ideation in children with ADHD, especially in the first month of treatment [35].

Clonidine has been evaluated for the treatment for ADHD in children with co-existing conditions, especially sleep disturbance. In a double-blind, randomized, placebo-controlled study of 122 children given clonidine, methylphenidate, or both, the authors concluded that methylphenidate offered a better combination of efficacy and tolerability compared to clonidine [50]. Clonidine was efficacious but was also associated with increased sedation.

The Multimodal Treatment Study of Children with ADHD was a 14-month trial of specific medication management, intensive behavioral therapy (group and individual sessions, teacher consults, a classroom behavioral aide for 12 weeks, and a summer program), both medication and behavioral therapy, or ordinary community care [75]. This study revealed that combination treatment did not significantly differ from medication management alone on direct comparisons.

Multiple studies have shown that among children who have ADHD, 54% to 84% have ODD, 15% to 19% smoke or have other substance abuse disorders, and 25% to 35% have a learning or language problem [9]. Up to one-third of children with ADHD also have an anxiety disorder or depression, and approximately 16% meet the criteria for mania [9].

Comorbidities are also common in adults with ADHD. Based on the National Comorbidity Survey Replication, the odds ratio of an adult with ADHD having any mood disorder is 5.0, any anxiety disorder is 3.7, any substance use disorders is 3.0, and intermittent explosive disorder is 3.7 [6].