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ADHD in adults: Overdiagnosed or just the opposite?

By Dr Jaime Martinez - 25th Feb 2024

ADHD in adults

Attention deficit hyperactivity disorder (ADHD) is a well-established psychiatric condition in children that persists into adulthood. It is a neuropsychiatric disorder that is defined by symptoms of inattention, impulsivity, and hyperactivity. Around 5-to-7 per cent of children worldwide are affected by the disorder. Scientific research has revealed dysfunction in specific neurotransmitters, such as dopamine and noradrenaline, which help to transmit signals across synapses in the brain. Studies of brain function in individuals with ADHD have shown impairment in the regions responsible for control. In ADHD, certain behaviours may be inhibited, such as task initiation, impulse control, comprehension of consequences, working memory, and future planning.

Interactions between genetic and environmental factors result in the development of ADHD. Supporting evidence for the genetic causality consists of an 80 per cent correlation in identical twins. It is estimated that parents with ADHD have a 35-to-50 per cent probability of transmitting the condition to their offspring. Additionally, around 25 per cent of children with ADHD have a parent who has also been diagnosed with the disorder.

Executive functioning

ADHD is considered a dysfunction of executive functioning, predominantly a frontal lobe activity. Executive functioning includes behavioural inhibition, working memory, and motivational and emotional control, which includes refraining from impulsive actions and allowing another function to control behaviour; maintaining mental images that serve as maps to guide actions and remember the steps necessary to achieve a goal; the ability to contain and moderate emotional reactions; and the ability to manipulate information as part of planning and problem solving. Therefore, patients with ADHD show disability not only in attention and focus, but also in decision-making and emotional regulation.

While ADHD originates from genetics, research implies that certain factors including parenting, education, traumatic experiences, brain injury, epilepsy, cognitive impairments, and comorbidities can potentially affect its severity throughout an individual’s life. A thorough evaluation by an experienced paediatrician, clinician, or psychiatrist is necessary to comprehend the impact of ADHD on the patient’s daily functioning and quality-of-life, and to prescribe the most appropriate treatment. Several indications defined as ADHD symptoms of inattention are, in fact, markers of executive function deficits. Executive functions encompass a broad range of central control procedures in the brain that activate, integrate, and manage other brain functions.

Types of ADHD

There are currently three known presentations of ADHD: The predominantly inattentive type, with symptoms such as being easily distracted, forgetfulness, daydreaming, poor concentration, disorganisation, and difficulty completing tasks; the predominantly hyperactive-impulsive type, characterised by hyperactivity, excessive fidgeting, restlessness, and difficulty waiting or remaining seated; and the combined type that involves characteristics of both.


It is difficult to estimate the exact number of people with ADHD because of variations in the criteria used for diagnosis, and in the sources of information used in research. However, rates are similar between countries and differences in rates mainly depend on the method of diagnosis. ADHD is diagnosed using either the International Classification of Diseases, 10th revision (ICD-10) or the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). European countries usually use ICD-10 by the World Health Organisation, while North America and Australia use the DSM-5 criteria for diagnosis.

The Health Service Executive (HSE) provides guidance for the Republic of Ireland through the ADHD in Adults-National Clinical Programme, with the aim of improving the recognition, diagnosis, quality of care, and support for individuals with ADHD. Based on the results of a comprehensive review, it has been estimated that between 5 and 7 per cent of children and young adults have ADHD. Rates have been found to be similar across cultures. According to American Psychiatric Association (APA) statistics and the DSM-5 criteria published in 2013, an estimated 8 per cent of children and 2.5 per cent of adults have ADHD. Although there is currently no specific data on the prevalence of ADHD in Ireland, data from the 2016 Census shows that 156,968 people (3.3 per cent) have difficulties learning, remembering, or concentrating, and ADHD is known to be the most common diagnosis in school-aged children.

Nowadays, there is a National Clinical Programme for ADHD in Adults in Ireland. Teams accept referrals from both adult and child community mental health teams. These new teams are in various stages of development, with some already operational. ADHD is more prevalent in boys than girls, with boys being diagnosed with ADHD approximately four times more often than girls. This is supported by data from the Central Statistics Office in Ireland, which reports that almost twice as many boys aged five-to-19 years experience learning, memory, or concentration difficulties compared to girls.

According to the National Institute for Health and Care Excellence (NICE), UK, ADHD should only be diagnosed on the basis of a combination of evidence from a full developmental and psychiatric history, a full clinical and psychosocial assessment (including tests), and observations and reports of the individual’s mental state.


The treatment of ADHD begins with confirming the diagnosis. This should be followed by explaining how the patient’s symptoms relate to the diagnosis, but ADHD is a condition that is often overlooked, under-treated, and often co-exists with other conditions. A general lack of awareness and understanding of ADHD within the medical community and wider society is the first barrier to diagnosing ADHD in adults. This lack of recognition has resulted in healthcare professionals not receiving the necessary training to recognise the symptoms of ADHD in adults, as well as an underestimation of the prevalence of the condition.

Research suggests that undiagnosed and untreated ADHD can lead to unstable relationships, and a decline in work and academic performances. Besides, there is an increased risk of other mental health problems. Although medication can significantly improve symptoms, it is not always enough. When dealing with children or adolescents, it is important for parents to implement learning strategies and new parenting methods. For adults, accommodations may be needed in the workplace.


Comorbid mental health issues, particularly anxiety and depression, frequently occur among individuals without psychoses who seek adult services, with up to 15 per cent being unaware of their existing ADHD. This comorbidity can affect compliance and response to treatment in patients with ADHD. In a clinical assessment, one or more of these disorders may be detected, and it is crucial to acquire appropriate care for these symptoms. Several psychiatric and personality disorders are commonly comorbid with ADHD.

Psychiatric disorders associated with ADHD include anxiety disorders, depression, dysthymia, social phobia, substance use disorders, eating disorders, autism spectrum disorders, learning disabilities, dyspraxia, conduct disorder, self-harm, suicide attempts, personality disorders, oppositional defiant disorder, sleep disorders, and Tourette’s syndrome. The most commonly reported personality disorders in patients with ADHD are antisocial personality disorder, borderline personality disorder, and histrionic traits.

ADHD is associated with a range of problematic behaviours, including oppositional defiance, substance abuse, and criminality. Patients with both ADHD and substance use disorders have a tendency to develop an addiction sooner, relapse more frequently, and need more hospitalisations than those without ADHD.

In several studies, many people with ADHD perceived themselves as having an addictive personality, leading to drug use. Some also reported difficulties at school as a result of substance misuse. Others felt that their substance use minimised their symptoms. Some individuals consume alcohol, nicotine, or marijuana as unhealthy coping mechanisms to alleviate stress. The use of cocaine and other drugs may also provide temporary relief, but can have serious consequences. People with ADHD are also at risk of initiating substance use at an earlier age than the general population.

Patients may be misdiagnosed with mood disorders like anxiety and depression since ADHD symptoms such as inattention, poor focus, memory loss, and distractibility tend to persist in those with the disorder. Children with ADHD are at risk for substance abuse disorders; therefore, these should also be thoroughly evaluated.

ADHD in adults

Although it is commonly believed that ADHD only affects children, research has shown that the disorder often persists into adulthood. However, the symptoms of adults with ADHD are typically more subtle than the symptoms of childhood. It is estimated that adult ADHD affects approximately 2.5-to-4 per cent of the general population. Because the symptoms of ADHD in adults may differ from those in children, identification is often more complex. Whereas children with ADHD are generally hyperactive and struggle to maintain focus on specific tasks, adults may display subtler symptoms, such as distractibility, impulsiveness, issues with task organisation, or procrastination. These symptoms are frequently misinterpreted as personality traits or linked to stress or anxiety.

An adult with ADHD may struggle to effectively activate and control several functions at the same time, including paying attention, starting and stopping actions, staying alert, exerting oneself, and using short-term memory. Attention deficit and impulsivity could lead to accidents at the workplace, at home, and while driving, as well as difficulties in relationships, interpersonal communication, and work performance. Consequently, individuals may experience feelings of sadness and failure. Anxiety problems are quite common among adults diagnosed with ADHD.

ADHD and general functioning, work, and education

The distractibility, disorganisation, and impulsivity associated with attention deficit ADHD can cause problems in many aspects of adult life. However, these symptoms can be particularly damaging to close relationships. People with ADHD often face challenges with their partners because of their symptoms. Their tendency to interrupt others, poor listening skills, and constant activity can make them easily distracted and cause them to miss important appointments or social events. This behaviour can also lead to irresponsible financial decisions, causing conflict, tension, and frustration in personal and professional relationships. Researchers also suggest that their impulsive, oppositional interpersonal style may inhibit social connections.

ADHD interferes with functioning and development. This may also apply to non-working adults and is often dismissed in this population. For example, a stay-at-home adult may have difficulty getting children to school on time, organising the home, and paying attention while driving, which affect functioning and daily life, even though the person is not at work or school. It is important to take this into consideration when making a diagnosis and when we analyse the global impact of this symptomatology on daily life.

Individuals who have faced challenges in the past with their education, career, and personal relationships may display restlessness as they strive to accomplish several tasks simultaneously with limited success. ADHD and college can be a powerful combination. It leads to a continuation of executive dysfunction, but with more complicated schedules and challenging courses.

It is common for university students with ADHD to face greater academic, organisational, and social difficulties in their learning experience. It also leads to delayed social maturity and decision-making skills, with temptations to lose focus.

Evidence suggests that students with ADHD are less confident than their peers when it comes to academic performance, and worry about their ability to concentrate and remember information, as well as managing time and procrastinating. In conclusion, managing ADHD at university is usually challenging.

Untreated or ineffectively treated ADHD can have a significant impact on all aspects of adult life, including work, family, psychological health, and overall life quality. Nonetheless, some adults with ADHD may appear to function normally despite the excessive effort they put in to compensate for their impairments. However, persistent symptoms, such as restlessness and mood instability can still cause psychological distress.

Diagnosis and management

ADHD is probably the most common undiagnosed chronic psychiatric condition in adults, but the primary symptoms can be less obvious and may present as secondary problems, with symptoms such as procrastination, mood swings, and low self-confidence. Adults with ADHD often experience co-existing mental disorders, which can make it difficult to recognise their underlying ADHD symptoms. This results in many individuals being misdiagnosed or treated only for their secondary symptoms, without addressing the root cause.

Under-recognition of ADHD in adults may be due to the mistaken belief that ADHD does not persist into adulthood, uncertainty about diagnostic criteria in adults, and the belief that ADHD is less severe than other comorbid disorders. It is possible that a person may not receive a diagnosis of ADHD until adulthood, as their teachers or family may not have recognised the condition when they were younger, they may have had a milder form of the disorder, or they may have managed satisfactorily until encountering the challenges of adulthood.

Untreated or incompletely treated ADHD can have negative impacts on almost all aspects of adult life, including employment, education, family, mental health, and overall wellbeing. Nevertheless, a few adults with ADHD may appear to function normally outwardly whilst having to put in extra effort to compensate for their disabilities, leading to continuous psychological stress caused by symptoms. If not properly diagnosed and treated, adults with ADHD often find it difficult to manage personal and professional relationships and to regulate their emotions, and unfortunately, underdiagnosed and untreated ADHD in adults can significantly affect quality-of-life.

A multidisciplinary team of professionals is essential in the diagnosis and treatment of ADHD, and the size of the team should vary according to the specific case. A comprehensive treatment may include medication, cognitive behavioural therapy, and occupational therapy, if available. There are different psychotropic drugs that have shown high efficacy in treating key symptoms of ADHD. A thorough clinical and physical examination should be held prior to commencing any medical treatment, as well as follow-up consultations for dose adjustment. Stimulants like methylphenidate and lisdexamfetamine are the first choice, followed by atomoxetine, guanfacine, and other off-label drugs such as bupropion, etc.


This article has examined ADHD, and the impact the disorder can have on all aspects of a person’s life. Increased awareness of ADHD symptoms and the use of diagnostic tools are needed in general health services, particularly in psychiatric practice, to identify the disorder in adults and help these patients to cope with their ongoing difficulties throughout their lives.

References on request

Author: Dr Jaime Martinez , Consultant Psychiatrist, MD MCPsycI

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