Attention Deficit Hyperactivity Disorder (ADHD)

ADHD is one of the most commonly occurring and most commonly misunderstood neurodevelopmental conditions. It affects an estimated 5-7% of children and 2-5% of adults worldwide -- in Singapore, this translates to a substantial number of people navigating school, work, and relationships with an unrecognised neurological condition.

The prevailing image of ADHD -- a hyperactive boy unable to sit still in class -- captures only a fraction of the clinical picture. Many people with ADHD are not hyperactive. Many are not diagnosed in childhood. Many are female. Many are high-functioning adults whose intelligence and determination have masked their difficulties for decades, only for the demands of adulthood to eventually exceed their coping capacity.

What is Attention Deficit Hyperactivity Disorder (ADHD)?

ADHD is a neurodevelopmental condition -- meaning it arises from differences in how the brain develops and functions, not from poor parenting, lack of discipline, or personal failing. It is characterised by a persistent pattern of inattention and/or hyperactivity-impulsivity that is present across multiple settings, inconsistent with the person's developmental level, and that directly impairs their functioning.

The core neuroscientific basis of ADHD involves differences in the prefrontal cortex -- the area of the brain responsible for executive functions: planning, prioritisation, working memory, impulse control, and self-regulation. People with ADHD have executive function profiles that are inconsistent with their general intelligence, which is why the phrase 'they just need to try harder' fundamentally misunderstands the condition.

ADHD is highly heritable -- approximately 75-80% of the variance in ADHD is accounted for by genetic factors. If a parent has ADHD, their child has a 40-50% chance of also having ADHD.

The Three Presentations of ADHD

The DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition) classifies ADHD into three presentations based on which symptom domain predominates. Understanding the presentation type is clinically important because the symptoms look different, the populations most affected differ, and the treatment priorities may vary.

Predominantly Inattentive Presentation

The defining feature is difficulty sustaining attention, not hyperactivity. This presentation is more common in girls and in adults, and is frequently missed because it does not cause obvious disruptive behaviour. The child or adult appears to be daydreaming, forgetful, or disorganised rather than disruptive -- and is often labelled as lazy, unmotivated, or underperforming rather than recognised as having a neurological condition.

Key signs: Fails to pay close attention to details; difficulty sustaining attention in tasks; seems not to listen when spoken to directly; does not follow through on instructions; difficulty organising tasks; avoids tasks requiring sustained mental effort; frequently loses things; easily distracted; forgetful in daily activities.

Predominantly Hyperactive-Impulsive Presentation

The defining features are excessive motor activity and difficulty controlling impulses. Children with this presentation are typically identified earlier because the behaviour is noticeable and disruptive in classroom settings. In adults, overt hyperactivity often diminishes, replaced by internal restlessness, difficulty relaxing, and impulsive decision-making.

Key signs: Fidgets or squirms; leaves seat when remaining seated is expected; runs or climbs inappropriately; unable to play quietly; always on the go; talks excessively; blurts out answers; difficulty waiting turn; interrupts or intrudes on others.

Combined Presentation

The majority of children diagnosed with ADHD have the combined presentation -- meeting criteria for both inattention and hyperactivity-impulsivity. This presentation is most easily recognised in childhood and typically responds well to treatment with medication and behavioural strategies. Adults with combined presentation may find that hyperactivity decreases with age while inattention and executive function difficulties persist.

Key signs: Meets criteria for both inattentive and hyperactive-impulsive presentations above. Symptoms cause significant functional impairment across two or more settings (home, school, work, relationships).

ADHD in Women and Girls: An Underrecognised Presentation

ADHD in females is one of the most significant areas of underdiagnosis in child and adult psychiatry. Girls and women are diagnosed at approximately half the rate of boys and men -- not because they are affected less frequently, but because their ADHD typically presents differently and is consistently missed.

Why ADHD is harder to recognise in girls

• Girls with ADHD more often have the inattentive presentation, without the disruptive hyperactive behaviour that prompts teacher referrals
• Girls are more likely to internalise their ADHD symptoms -- developing anxiety, low self-esteem, and perfectionism as compensatory strategies
• Girls tend to be more socially motivated and better at masking difficulties in social situations
• The societal expectation that girls should be quiet and compliant means that inattentive, disorganised girls are less likely to be flagged as problematic
• Girls with ADHD are significantly more likely to be diagnosed with anxiety or depression -- which may be real comorbidities, but may also be masking the underlying ADHD

How ADHD presents in adult women

• Chronic feelings of overwhelm despite significant effort
• Difficulty with household management, planning, and following through on intentions
• Emotional dysregulation -- disproportionate emotional responses, sensitivity to criticism, rapid mood shifts
• Rejection sensitive dysphoria (RSD) -- intense emotional pain in response to perceived rejection or failure
• Difficulty reading long documents, following conversations, or completing administrative tasks
• A pattern of starting many projects and completing few
• Exhaustion from the constant effort of compensating and masking

Women who identify with the above and have wondered throughout their lives why everyday tasks feel harder for them than for others -- often initially diagnosed with anxiety, depression, or burnout -- are encouraged to consider a formal ADHD assessment.

Common Comorbidities

• Anxiety disorders: The most common comorbidity; anxiety may be primary (coexisting with ADHD) or secondary (arising from the chronic stress and underperformance associated with unmanaged ADHD)
• Depression: Particularly common in adults with ADHD; often a consequence of years of underachievement, relationship difficulties, and low self-esteem
• Specific learning disorders: Dyslexia, dysgraphia, and dyscalculia co-occur with ADHD at significantly elevated rates
• Autism Spectrum Condition (ASC): ADHD and autism co-occur in approximately 30-50% of cases; both can be diagnosed in the same individual under DSM-5
• Sleep disorders: Delayed sleep phase syndrome and poor sleep quality are extremely common in ADHD and significantly worsen all ADHD symptoms
• Substance use: Untreated ADHD significantly increases the risk of substance use disorders; effective ADHD treatment reduces this risk
• Oppositional defiant disorder (ODD) and conduct disorder: More common in children with ADHD, particularly the hyperactive-impulsive presentation

Identifying and treating comorbidities is essential -- treating ADHD alone when significant anxiety or depression is also present produces inferior outcomes compared to treating both. A comprehensive assessment should screen for the above conditions.

ADHD in Singapore: Educational and Cultural Context

Singapore's high-performance educational culture creates a particular context for ADHD -- one that can both hide and amplify its impact.

• The structured, high-stakes examination system (PSLE, O-levels, A-levels) places intense demands on exactly the executive functions that ADHD impairs: sustained attention, organisation, time management, and working under pressure
• High parental and societal expectations can lead to misattribution of ADHD difficulties as laziness, lack of effort, or poor attitude -- delaying diagnosis and adding shame to functional impairment
• Gifted students with ADHD may compensate through intelligence until later years, when the demands of secondary school or university exceed their coping strategies
• Cultural reluctance to seek psychiatric assessment for children -- concerns about stigma, labelling, or the implications of a psychiatric diagnosis -- can delay diagnosis by years
• School-based support (learning support, extended exam time, separate examination venues) is available in Singapore for students with a formal ADHD diagnosis -- making early and accurate diagnosis practically important beyond its clinical value

At Farrer Park Hospital, all consultations are strictly confidential. A psychiatric diagnosis does not appear on medical reports without your consent and does not affect employment or insurance in the ways many patients fear.

How is ADHD Diagnosed?

ADHD diagnosis is a clinical process requiring a comprehensive assessment by a trained psychiatrist, psychologist, or developmental paediatrician. There is no blood test, brain scan, or single questionnaire that diagnoses ADHD -- diagnosis requires clinical judgement applied to a thorough history and validated assessment tools.

• Clinical Interview: A detailed history covering symptom onset, duration, and impact across settings (home, school, work, relationships). For adults, retrospective childhood history is required. For children, both parent and child perspectives are gathered. The interview also screens for comorbid conditions and excludes other explanations for symptoms.
• Rating Scales and Questionnaires: Validated self-report and informant-report scales: Conners' Rating Scales, Vanderbilt ADHD Diagnostic Rating Scales (children), ADHD Rating Scale (ADHD-RS), Adult ADHD Self-Report Scale (ASRS). These provide standardised, norm-referenced measurements of symptom severity and do not replace clinical assessment.
• School or Workplace Reports: Reports from teachers (for children) or employers (for adults) provide collateral information across a different setting. DSM-5 requires that symptoms are present in two or more settings. School report cards, teacher comments, and academic history are reviewed.
• Neuropsychological Testing: Formal cognitive and neuropsychological testing assesses working memory, processing speed, attention, and executive function. Not required for all ADHD assessments but particularly useful when learning disorders are suspected, when the diagnosis is unclear, or when educational accommodations require objective cognitive data.
• Medical History and Physical Examination: Thyroid disorders, sleep disorders, sensory impairments (hearing, vision), and certain medications can produce ADHD-like symptoms. A medical review excludes these alternative causes and identifies any relevant physical health considerations before medication is prescribed.
• Developmental and Family History: ADHD is highly heritable. A family history of ADHD, learning difficulties, or related conditions supports the diagnosis. Developmental milestones, birth history, and early childhood history are relevant for both child and adult assessments.