What are the main symptoms of ADHD?

Three key features define attention-deficit hyperactivity disorder (ADHD) or hyperkinetic disorder (HKD)1,2:

  • Inattention
  • Hyperactivity
  • Impulsivity.

What is inattention?

Inattention is characterised as an individual moving between tasks without completing any one activity, seemingly losing interest in one task because they become diverted to another.1,2 Individuals with inattention are often easily distracted and forgetful, and experience difficulties when organising activities.1,2

What is hyperactivity?

Hyperactivity refers to excessive motor activity,1,2 which may present differently depending on the individual’s age1 and may be more evident in structured situations that require self-control.2

What is impulsivity?

Individuals with impulsive tendencies can be reckless and appear impatient, and are often disinhibited in social situations. They may find it difficult to wait their turn, intruding on or interrupting others’ activities or blurting out answers to a question before it has been completed.1,2


The contribution of each symptom to the presentation of ADHD varies from person to person.1 In some individuals, two or more features may contribute in equal measure; in others, one feature may predominate.1


How do the symptoms of ADHD change across the lifespan? | Dr David Coghill | Royal Children’s Hospital, Melbourne, Australia

How are the symptoms of ADHD measured?

Different features of ADHD can impair functioning and quality of life in different ways,3-6 so it is important to accurately evaluate each individual’s unique symptomatic characteristics. Symptoms are measured using medical classification systems (see diagnosis) such as the Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5TM) or the International Classification of Diseases 11th Revision (ICD-11).1,2 Both classification systems categorise individuals with ADHD by three main presentations1,2:

  1. Combined type
  2. Predominantly inattentive type
  3. Predominantly hyperactive-impulsive type.

Are there any psychiatric comorbidities associated with ADHD?

Symptoms of ADHD can overlap with those of other related disorders. Therefore, care in differential diagnosis is needed. When there are coexisting psychiatric conditions, it is important to try and differentiate the level of impairment due to ADHD, because this will guide the treatment plan.7 Common coexisting conditions in children with ADHD include disorders of anxiety, conduct, language and communication, learning, mood and motor control (Figure 1). Adults with ADHD may also commonly have bipolar disorder, obsessive-compulsive disorder, personality disorders and substance-use disorder (Figure 2).7

Figure 1: ADHD and psychiatric comorbidities in children and adolescents: descriptive overlapping and distinct features. Figure developed from CADDRA ‒ Canadian ADHD Resource Alliance: Canadian ADHD Practice Guidelines, 4.1 Edition, Toronto ON; CADDRA, 2020.8 Note that these are examples only and not an exhaustive list.

ADHD and psychiatric comorbidities in children and adolescents


Figure 2: ADHD and psychiatric comorbidities in adults: descriptive overlapping and distinctive features. Reproduced with permission from Katzman MA et al. BMC Psychiatry 2017; 17: 302.9*

ADHD and psychiatric comorbidities in adults


*A review by Katzman et al. discussed the most frequent comorbid psychopathologies, mood and anxiety disorders, substance-use disorders and personality disorders, and the challenges presented for diagnosis and treatment due to overlapping symptoms of ADHD and psychiatric comorbidities in adults. The review included that this overlap between disorders has led to the proposal that diagnosis and treatment of ADHD may be considered on a spectrum using a dimensional rather than a categorical approach.9

  1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. 2013.
  2. World Health Organization. ICD-11: International Classification of Diseases 11th Revision. 2018. Available at: https://icd.who.int/. Accessed January 2021.
  3. Caci H, Asherson P, Donfrancesco R, et al. Daily life impairments associated with childhood/adolescent attention-deficit/hyperactivity disorder as recalled by adults: results from the European Lifetime Impairment Survey. CNS Spectr 2015; 20: 112-121.
  4. Gudjonsson GH, Sigurdsson JF, Eyjolfsdottir GA, et al. The relationship between satisfaction with life, ADHD symptoms, and associated problems among university students. J Atten Disord 2009; 12: 507-515.
  5. O’Callaghan P, Sharma D. Severity of symptoms and quality of life in medical students with ADHD. J Atten Disord 2014; 18: 654-658.
  6. Grenwald-Mayes G. Relationship between current quality of life and family of origin dynamics for college students with attention-deficit/hyperactivity disorder. J Atten Disord 2002; 5: 211-222.
  7. NICE guideline 2018. Attention deficit hyperactivity disorder: diagnosis and management. Available at: https://www.nice.org.uk/guidance/ng87. Accessed January 2021.
  8. Canadian ADHD Resource Alliance (CADDRA). Canadian ADHD Practice Guidelines. Edition 4.1. Toronto, ON: CADDRA, 2020.
  9. Katzman MA, Bilkey TS, Chokka PR, et al. Adult ADHD and comorbid disorders: clinical implications of a dimensional approach. BMC Psychiatry 2017; 17: 302.
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