The Mental Health Impacts of Undiagnosed ADHD in Adulthood

The Mental Health Impacts of Undiagnosed ADHD in Adulthood

Author: Claudia M. Elsig, MD

ADHD is increasingly recognised and diagnosed in children, but what about adults? Evidence suggests it is much harder to diagnose ADHD in adults and is easily missed because it is confused with other mental health problems. 

Going through life with an undiagnosed problem that affects behaviour is a huge burden. Undiagnosed, ADHD can lead to excessive frustration, irritability, and low self-esteem and cause chronic stress, significantly affecting relationships and life outcomes.

Research shows that adult ADHD is vastly under-recognised and undertreated across countries and cultures.1 Here, we discuss the mental health impacts of undiagnosed ADHD in adulthood.

What is ADHD?

ADHD stands for ‘attention deficit hyperactivity disorder’. Characterised by difficulty sustaining attention, hyperactivity and impulsivity, ADHD is a neurodevelopmental condition that affects how the brain works and develops.

Most commonly, people with ADHD display both hyperactive-impulsive behaviours and inattention. But they may be predominantly one or the other (hyperactive-impulsive or inattentive). Where hyperactivity isn’t present, the condition is often called ADD (attention deficit disorder).

ADHD is one of the most common mental disorders affecting children and is diagnosed more often in boys than girls.2 This is because girls tend not to show atypical hyperactivity, meaning diagnoses get missed because the symptoms are less noticeable. 

The symptoms of ADHD are much more difficult to define in adults, and it is, therefore, much easier for them to be confused with other psychiatric disorders.

What causes ADHD?

ADHD is a complex mental health condition, meaning multiple factors are involved in its development. While the exact causes are not yet fully understood, it is widely accepted that genetic and environmental factors are key influences. ADHD tends to run in families. 

Overexposure to pesticides has also been linked to ADHD. Rutgers’ study found that a commonly used pesticide can alter the development of the brain’s dopamine system, which is responsible for emotional expression and cognitive function.3

Recent research also considers the role of viruses. For example, one study found a likely association between cytomegalovirus infection and ADHD.2

Certain groups of people, such as those born prematurely, are also at risk. People with brain damage and people with epilepsy are also more susceptible.

What is the prevalence of ADHD?

According to the UK’s National Institute for Health and Care Excellence (NICE), the global prevalence of ADHD in children is around 5 per cent. In comparison, in studies based on US populations (where rates of diagnosis and treatment tend to be highest), the rate is estimated at between 8 and 10 per cent. In the UK, NICE reports that adult ADHD affects approximately 3-4 per cent of the population.4

A global systematic review and meta-analysis to ascertain the prevalence of adult ADHD worldwide show that 366.33 million adults were affected in 2020 globally.5

What are the most common symptoms of ADHD in adults?

The symptoms of ADHD vary considerably from person to person but commonly include some or all of the following:

  • Difficulty concentrating
  • Easily distracted
  • Making careless mistakes, for example, at work
  • Forgetfulness and easily losing things
  • Inability to stick to one task or constantly changing from one task to the next
  • Poor listening skills and difficulty following instructions
  • Talking a lot and interrupting others – may blurt out answers and talk over others
  • Disorganised
  • Hyperactivity or fidgeting and inner restlessness
  • Impulsiveness
  • No sense of danger
  • Unable to deal with stress
  • Difficulties with timekeeping and time management
  • Unable to commit and feeling overwhelmed when making decisions

How is ADHD diagnosed?

There are no laboratory tests for ADHD, such as blood tests, x-rays or a brain scan. Diagnosis is made by a mental health professional using an evaluation process. They will consider many factors when determining if a person has ADHD, including the severity and duration of symptoms and whether they negatively affect the person’s quality of life.

In children, problems are usually noticed by parents or teachers at school. In adults, diagnosis is trickier as symptoms may not be as clear and may become muddled with other mental health issues, like anxiety or depression. 

In adults, there may be less hyperactivity than in children, but an adult with ADHD may still struggle with impulsiveness, restlessness and difficulty paying attention. Notably, adults’ ADHD symptoms may be less evident if they get help from a partner (i.e. managing their time) or have chosen a career that allows rapid task switching. In adults, often symptoms are mistaken for quirky characteristics.

Once recognised, referral to a mental health specialist is the usual route to confirm a diagnosis of ADHD. Usually, a person must display at least five diagnostic criteria, including inattentiveness, hyperactivity and impulsiveness, or a combination of these.

Different health systems worldwide may use slightly different criteria/diagnostic tools. Read more about the symptoms and diagnosis of ADHD in the US here, and learn more about how ADHD is diagnosed in the UK here.

Can someone suddenly develop ADHD as an adult?

Most people with ADHD in adulthood have had the disorder since childhood. Adults don’t usually suddenly develop symptoms of ADHD as an adult, unless there is a brain injury or the onset of epilepsy. 

Many go undiagnosed in childhood but may receive a diagnosis as an adult. Girls are more likely to make it to adulthood without a diagnosis, as ADHD symptoms are harder to spot in girls. And females appear to have better-coping mechanisms than males, so they can more easily hide symptoms.

A late diagnosis (as an adult) often happens because covering up or hiding ADHD symptoms becomes harder in adulthood as individuals lose the structure of school and face new responsibilities and increased daily life stresses.

Research into adult ADHD is ongoing. Emerging evidence suggests that adults can develop ADHD (i.e. it wasn’t present in childhood). For example, findings in one study showed that 90 per cent of the individuals with adult ADHD at age 38 years had not met the criteria for the disorder in childhood.6

However, Dr Michael Manos, PhD, founding Director of Cleveland Clinic’s ADHD Center for Evaluation and Treatment, doesn’t adhere to the hypothesis that childhood and adult ADHD are two distinct conditions. He says, “It’s not that someone can outgrow or grow into ADHD. It’s whether or not the symptoms — which were probably always there — are impairing. Adaptability, the means to manage or even leverage ADHD symptoms, is what changes throughout life.”7

Why does ADHD go undiagnosed or misdiagnosed?

Sadly, two-thirds of mental health problems go undiagnosed and untreated. ADHD is complex, and symptoms can present quite differently in individuals. The symptoms of ADHD can also mimic several other mental disorders, so it can be hard to diagnose. There are many different causes for restlessness and difficulty concentrating, for example.

Despite extensive studies, the causes of ADHD remain poorly understood. Research shows that substantial controversy exists regarding a correct diagnosis of ADHD and that there are areas of subjectivity in diagnosis.8 Considerable variation also exists in diagnosis between genders.

But getting a diagnosis is important. The symptoms of ADHD can cause feelings of guilt, shame, and embarrassment about not being able to function in the same way as peers. It can be incredibly frustrating for a person with ADHD. A diagnosis can help to reduce these heightened emotions.

What other disorders overlap with ADHD?

The most common psychiatric conditions that have symptoms in common with ADHD are:

  • Mood disorders
  • Anxiety disorders
  • Substance abuse disorders
  • Obsessive-compulsive disorder (OCD)
  • Antisocial personality disorder
  • Borderline personality disorder
  • Bipolar disorder
  • Autism

In addition, chronic fatigue, hormonal disorders, insomnia and lack of sleep can cause people to struggle with concentration and focus, thus mimicking symptoms of ADHD or exacerbating them.

What are the mental health impacts of untreated ADHD in adulthood?

Many adults may be unaware they have ADHD. This may lead to a frustrating life, missing meetings, forgetting things, a high level of impatience, inability to control anger (outbursts), mood swings, poor planning, difficulty multi-tasking, and trouble coping with stress. Life with ADHD can feel out of control and overwhelming.

Anxiety, depression, conduct disorder (persistent patterns of antisocial, aggressive or defiant behaviour), alcohol and substance abuse, and sleep problems are also more common in people with ADHD.

The consequences of ADHD can be severe, affecting work performance and professional and personal relationships. People with ADHD can appear hectic or chaotic and may struggle to manage finances.

Individuals living with undiagnosed ADHD are also more likely to have motor vehicle accidents because of risky behaviours – a person with ADHD has trouble filtering out distractions and lacks focus.

Emotional dysregulation is one of the most misunderstood aspects of ADHD, often leading to misdiagnosis with other mental health conditions.9 Commonly, depression, bipolar disorder or borderline personality disorder (BPD) are diagnosed instead. 

People with undiagnosed ADHD are more likely to have relationship problems. There is a certain level of dysfunction, misaligned objectives, and increased tension, which can be frustrating for a partner. Unsurprisingly, people with ADHD have higher rates of divorce. Parents with ADHD may also have frustrating and conflict-ridden relationships with their children.

What is the treatment for ADHD?

ADHD isn’t a curable illness but can be managed effectively with the right treatment plan. This could include:

  • Specialist coaching and psychotherapy
  • Medication (stimulant or non-stimulant)
  • Nutritional advice
  • Well-being and holistic health management
  • Mindfulness and meditation

ADHD, when treated well, also has its positives. Many high-achieving individuals have ADHD. In fact, success often goes together with the condition. It is common knowledge that high energy, impulsivity, and risk-taking are common traits of CEOs and entrepreneurs. Some well-known, high-achieving ADHD sufferers include Richard Branson, Bill Gates and Walt Disney.

The role of psychotherapy in the treatment of ADHD

Psychotherapy is an effective treatment option for ADHD as it helps people to manage their symptoms and behaviours better. A systematic review of psychological treatments in adult ADHD found strong empirical support for Cognitive Behavioral Therapy interventions. In addition, findings indicated support for the effectiveness of Mindfulness, Dialectical Behavior Therapy and Neurofeedback.10

Getting help for ADHD at CALDA

At CALDA, we are experienced in treating and supporting UHNWIs with ADHD. We create a personalised treatment program; we use scientifically based methods from classical medicine combined with tested treatment methods from complementary medicine, traditional Chinese medicine (TCM) and orthomolecular medicine. 

Our programs address any imbalances through nutritional support, supplements and exercise, and intense psychotherapy sessions help you understand your behaviours and equip you with practical ways to better manage and cope with everyday situations.

Read more about the CALDA Concept here, or for a discreet, no-obligation chat with our lead psychiatrist, Dr Claudia M. Elsig, please get in touch.


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  2. Zhou R, et al. 15 Aug 2015. Diagnosis of children’s attention deficit hyperactivity disorder (ADHD) and its association with cytomegalovirus infection with ADHD: a historical review. Int J Clin Exp Med. 2015 Aug 15;8(8):13969-75.
  3. Lally, R. 29 Jan 2015. Rutgers Website. Common Pesticide May Increase Risk of ADHD. [Accessed 15 Aug 2023].
  4. National Institute of Health and Care Excellence. Website. Last updated Nov 2022. Attention deficit hyperactivity disorder: How common is it? [Accessed 15 Aug 2023].
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  9. The ADHD Centre. Website. 11 Jan 2023. How Does Untreated ADHD Affect Adults? [Accessed 15 Aug 2023].