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Intellectual Disability: Information for Psychiatry Residents

Summary: Intellectual disability is a chronic developmental condition (previously known as mental retardation in the DSM-IV) which impacts a person’s adaptive functioning in conceptual, social and practical domains. Individuals with ID are at higher risk of presenting to psychiatrists with mental health and behavioural difficulties. Identifying individuals with ID as well as their severity is important, as they require different levels of support to reach their full potential.
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You are asked to see a 10-yo with intellectual disability (ID) due to problems with aggression at home and school. His aggression includes swearing, kicking others. Triggers include sensory issues, as well as teachers trying to ask him to follow the school routine. Unfortunately, his aggression is so severe that he is at risk of being suspended from school, which will cause extreme hardship to his mother, as she will then be at risk of losing her job. 

What are you going to do?

What is Intellectual Disability?

Intellectual disability (ID) is a chronic developmental disorder, with onset in the developmental period (i.e. before age 18), with impairment of general mental abilities which impacts adaptive functioning in three domains:

  1. Conceptual domain, which includes skills such as:
    • Language
    • Reading
    • Writing
    • Math
    • Reasoning
    • Knowledge
    • Memory
  2. Social domain, which are social and interpersonal skills such as:
    • Empathy
    • Social judgment
    • Communication skills
    • Ability to make and retain friendships
  3. Practical domain, the ability to self-manage in areas such as:
    • Personal care, health and safety
    • Ability to function at school or work
    • Manage money and finances
    • Recreation and leisure

Impairment of mental abilities is defined as significantly below, i.e. 2 standard deviations below the population, which means an IQ score of 70 or below.


There is variation in terms across the Western world:

  • Australia: 
    • Intellectual disability
  • North America:
    • With the DSM-5, the term is now Intellectual disability (or intellectual developmental disorder).
    • With the DSM-IV, the previously used term was mental retardation.
  • UK: 
    • Learning disabilities.

Developmental disability

  • Refers to various developmental disabilities, which includes intellectual disability as well as autism spectrum disorders and other developmental disorders.

Red Flags

Infants with language delays

  • No words by 12-months
  • No 2-word phrases by age 2
  • Parents concerned the child is deaf

Toddler with motor delays

  • Delays in self-feeding, toileting, dressing
  • Troubles with comprehension

Clinical Presentation

Borderline intellectual functioning

  • If symptoms are not identified while in school, they may even remain unidentified as adults.

Mild ID

  • Delays may not be noted in preschool years, but rather in school age.

Severe or profound ID

  • Significant delays in motor, language and social milestones may be noted earlier on such as within first 2-years of life


Individuals with intellectual disability (ID) may have difficulty in numerous domains:


  • Speech

Delayed language and difficulties speaking and expressing themselves

  • Perception

Difficulties with perceiving the environment, contributed to by sensory and processing issues.

  • Cognition

Impaired ability to understand and problem-solve.

  • Concentration

Impaired concentration

  • Emotions

May have problems with emotion development, as well as emotional control.

  • Coordination

May have problems with poor coordination; stereotyped movements.

  • Behaviours

May have aggression. Many factors such as lack of communication skills, ability to problem-solve, sensory issues may contribute to disruptive and aggressive behaviors.

  • Social and interpersonal

Tend to be gullible and naive, as they have troubles identifying risky situations due to their limitations in everyday reasoning and social judgment.

Higher risk of being taken advantage by others which includes:

  • Childhood abuse and trauma;
  • Bullying in school;
  • More serious exploitation in adulthood.

Presentation to Psychiatry

As a psychiatrist, you may encounter individuals with ID in various ways:

  • The diagnosis has already been made and they have been referred to you for mental health issues (e.g. depression, anxiety) and/or behavioural issues.
  • You are seeing a child/youth or adult for mental health issues, and you suspect they may have ID.


Prevalence of intellectual disability

  • 1% of the population


  • Males > females (due to sex-linked genetic factors; male vulnerability to brain insult)
    • Mild ID M:F = 1.6 : 1
    • Severe ID M:F = 1.2 : 1


There are many different causes of intellectual disability which include:

  • Known causes 60% (Curry, 1997)
  • Idiopathic (no specific known cause) 40% (Curry, 1997)

Known Causes

Prenatal (before birth)

Chromosomal disorders

Down’s Syndrome

Fragile X syndrome

Prader Willi syndrome

Klinefelter’s syndrome

Single gene disorders

Inborn errors of metabolism




Other genetic conditions

Cornelia de Lange

Adverse environmental influences

Maternal infections such as rubella, syphilis, toxoplasmosis, cytomegalovirus, HIV

Exposure to alcohol, drugs, toxins

Maternal disease (e.g. diabetes)


Perinatal (around the time of birth)

Third Trimester

Complications of pregnancy

Diseases in mother (e.g. diabetes)

Placental disease

Labour (during delivery)

Labor/delivery-related events leading to neonatal encephalopathy

Complications of prematurity: ischemia, hypoxia, intra cerebral hemorrhage

Neonatal (first four weeks of life)

Septicemia, jaundice, hypoglycemia


Postnatal causes


Infections (such as meningitis, whooping cough or measles)


Head injury


Heavy metals such as lead, mercury


Prolonged malnutrition

Abuse and trauma

Severe and chronic social deprivation



Screen a child’s development at regular intervals (American Academy of Pediatrics), such as by using parental surveys:

  • Parents' Evaluation of Developmental Status (PEDS),
  • Ages and Stages Questionnaires (ASQ)
  • Child Development Inventories (CDI).

Diagnostic Measures

Psychologists may use common psychological tests such as:

  • Bayley Scales of Infant Development-III,
  • Stanford-Binet Intelligence Scale,
  • Wechsler Intelligence Scale for Children-IV,
  • Wechsler Preschool and Primary Scale of Intelligence-Revised,
  • Vineland Adaptive Behavior Scales-Second Edition (Vineland-II)
    • The “Vineland” is designed to measure adaptive behavior of individuals from birth to age 90.
    • Contains 5 domains
      • Communication
        • Receptive: How the individual listens and pays attention and what he or she understands.
        • Expressive: What the individual says, how he or she uses words and sentences to gather and provide information.
        • Written: What the individual understands about how letters make words, and what he or she reads and writes.
      • Daily Living Skills
        • Personal: How the individual eats, dresses, and practices personal hygiene.
        • Domestic: What household tasks the individual performs.
        • Community: How the individual uses time, money, the telephone, the computer, and job skills.
      • Socialization
        • Interpersonal Relationships: How the individual interacts with others.
        • Play and Leisure Time: How the individual plays and uses leisure time.
        • Coping skills: How the individual demonstrates responsibility and sensitivity to others.
      • Motor Skills
        • Gross Motor: How the individual uses arms and legs for movement and coordin
        • Fine Motor: How the individual uses hands and fingers to manipulate objects.
      • Maladaptive Behaviour (optional)
        • Any internalizing, Externalizing and other types of undesirable behavior that may interfere with the individual’s adaptive functioning.
    • Adaptive Behavior Composite: A composite of the communication, daily living skills, socialization, and motor skills domains.

Assessment / History of the Person with known (or suspected) ID

Ensure your physical space is safe, such as being mindful of sensory needs:

  • Reduce visual overstimulation, e.g. keep waiting rooms tidy, try to avoid harsh fluorescent lighting; dim lights if possible; allow patient to wear baseball cap, hoodies, etc.
  • Reduce auditory overstimulation, e.g. don’t have background radio in the waiting room.
  • Consider booking individuals with ID during quieter periods, e.g. first or last appointment of the morning/afternoon.

Communication recommendations (Kelly, 2011; Sullivan, 2018):

  • Is it an older youth or adult with ID?
    • Explain to caregivers that you will address patients directly (as opposed to simply turning to their caregivers) AND that you also want caregivers’ input as well.
  • Is it a child with ID?
    • Address caregivers primarily, in the same way as you would with other children AND ask the child for input when appropriate (e.g. asking about their thoughts/feelings, sensory issues, triggers and stresses) as well as meeting alone (when screening for neglect / abuse).
  • Engage the patient, e.g. around a preferred item that has been brought to the appointment; their clothing; ask about interests.
  • Communication aids used by those with ID may include
    • Signing (such as American Sign Language)
    • Picture exchange communication systems (such as on tablet device)

A comprehensive assessment would include the following:

  • Concerns
    • What are the main issues that are stressful, difficult, or troubling?
    • Any behaviours that are challenging for caregivers? (aka behaviours that challenge (BTC))?
  • Goals
    • What are the patient’s best hopes from the visit? (if patient is able to articulate, such as with those with mild ID)
    • What are the caregiver's best hopes from the visit?
  • Current services and supports
  • Any stressful life events?
    • E.g. abuse, neglect, bullying, exclusion.
  • Medication history
    • Review medications regularly (eg, every 3 mo), including the indication, when started / stopped, effectiveness, and any side effects (Sullivan, 2018)
  • Caregiver needs (Sullivan, 2018)
    • Ask caregivers about how they are coping, and if they have any particular needs.
  • Psychiatric review of symptoms including
    • Neurovegetative symptoms, e.g. sleep, energy, concentration, appetite.
    • Screening for abuse/trauma: Meet alone with the individual with IDD to screen for abuse, exploitation or neglect (Sullivan, 2018)
  • School / Workplace history
    • What schools were attended in the past? Were these mainstream, or in a specific program?
    • With adults: What work/ employment in the past?
  • Pregnancy history
  • Birth history
  • Developmental history
    • Language development
    • Sensory processing
    • Motor skills
    • Socialization
      • Any troubles with social skills
  • Family medical history
    • Genetic conditions?
    • Mother
      • Infections during pregnancy?
      • Any possibility of prenatal exposure to toxins?
      • Any consanguinity?
      • Fetal loss
    • Premature?

Physical Examination

As a psychiatrist, either perform, or ensure that there is a primary care provider who can provide physical examinations as necessary.


General observations


Child’s ability to communicate, social skills, eye contact, compliance, attention span, impulsivity, and style of play.

Dysmorphic facies? Consider flat, broad face of Down syndrome.

Obesity? Consider suggest Prader Willi

Any signs of abuse? E.g. unexplained injuries, bruises; choke marks around the neck; human bite marks, cigarette burns, unusual fractures


Short stature?

  • May suggest genetic disorder (e.g. Turner syndrome in females), fetal alcohol syndrome, or hypothyroidism.

Tall stature?

  • May suggest fragile X syndrome (FraX), or overgrowth syndrome associated with ID.


Monitor regularly, including body mass index, waist circumference (Sullivan, 2018)

Head and Neck

Assess vision (e.g. Snellen eye chart)

Assess hearing (e.g. whisper test) (Sullivan, 2018)

Head circumference


  • Correlates highly with cognitive deficits.


  • Associated with hydrocephalus; some inborn errors of metabolism]


Any murmurs?


Any wheezing (i.e. suggestive of asthma)

Any respiratory infections?


Any hard lumpy abdomen suggesting constipation


Any problems with gait/ coordination?

Tics / tremors?

Muscle tone: Low tone (i.e. Hypotonia) or spasticity?

Any neurologic deficits?

Strength and coordination

Deep tendon reflexes

Persistent primitive reflexes?


Abnormal movements such as dystonia or athetosis?


Hyperpigmented and hypopigmented macules?

  • May suggest café-au-lait macules (associated with neurofibromatosis type 1)
  • Ash-leaf spots (associated with tuberous sclerosis), fibromas


Any discomfort with limb movement, suggesting injuries or joint issues

Any pressure sores?

Any injuries from self-injurious behaviours?


Mental Status Examination (MSE)


Including hygiene, grooming, clothing and overall health status

Any signs of abuse/neglect?


Including stereotyped behaviours, involuntary movements, self-injury

Mood / affect

Any change in patient’s mood/affect from their usual baseline mood?


Level of speech, lack of speech, level of understanding, screaming or shouting


If formal testing for cognition and IQ has not been performed, try to estimate level of intellectual disability

Estimating Intellectual Disability Based on Level of Function

Mild ID

Can usually hold conversation with interviewer

Can usually achieve independence with self-care, activities of daily living

Troubles with academics, but capable of independent work

Moderate ID

Usually need assistance with interview from caregiver

Usually need supervision with self-care

May have basic reading, writing or counting skills

Can do tasks with supervision and engage in activities

Severe ID

Limited ability to communicate, requiring caregiver

Needs supervision with self-care

Commonly has physical issues such as epilepsy

Profound ID

Severely limited ability to communicate, requiring caregiver

May have physical issues such as problems with mobility, seizure disorder, incontinence


Spectrum of Intellectual Function

Intellectual Disability

Borderline intellectual functioning

Normal IQ

1% of the population


7% of the population


Majority of the population

IQ 50-55 to 70 (or below)


IQ 71-85


Still face significant challenges compared to those with “normal” IQ.

May perform daily activities and work without assistance but are more vulnerable to stressful life events and mental health concerns.



DSM-5 Intellectual Disabilities


DSM-5 Intellectual Disabilities are the following:


1. Intellectual disability (aka intellectual developmental disorder)

  • Previously known as mental retardation in DSM-IV


2. Global developmental delay (GDD)

  • The term GDD is used when a person is < 5 years of age and has significant deficits in learning and function, however reliable (IQ testing) assessment is not possible
  • GDD requires reassessment after a period of time (DSM-5)
  • A child with GDD will not necessarily test in the ID range when older.


3. Unspecified intellectual disability (ID)

  • The term “Unspecified ID” is used when a person is > 5 years age, and reliable assessment is not possible.

DSM-5 Intellectual Disability (Intellectual Developmental Disorder)

DSM-5 Criteria for ID 

A. Deficits in intellectual function

  • Deficits (reasoning, problem- solving, planning, abstract thinking etc) confirmed by clinical assessment and individual standardized testing (IQ: 70 ± 5).

B. Deficits in adaptive function

  • The person’s intellectual deficits lead to deficits in adaptive function, i.e the person is unable to meet socio-cultural standards for activities in daily life (at home, school, work, community) without ongoing support.

C. Age of onset is during the developmental period.



  • A diagnosis of ID is not made only on basis of IQ score (i.e. IQ ≤ 70) -- it requires troubles with adaptive functioning as well.


  • Severity for ID
    • Mild IQ 50-55 to 70
    • Moderate IQ 35-40 to 50-55
    • Severe IQ 20-25 to 35-40
    • Profound IQ < 20-25



Intellectual Function

Adaptive Function


85% of those with ID

IQ 50-70

Slower than typical in all developmental areas

No unusual physical characteristics

Able to learn practical life skills

Attains reading and math skills up to grade levels 3-6

Able to blend in socially

Functions in daily life


10% those with ID

IQ 35-49

Noticeable developmental delays (i.e. speech, motor skills)

May have physical signs of impairment (i.e. thick tongue)

Can communicate in basic, simple ways

Able to learn basic health and safety skills

Can complete self-care activities

Can travel alone to nearby, familiar places

People with moderate intellectual disability have fair communication skills, but cannot typically communicate on complex levels.

May have difficulty in social situations and problems with social cues and judgment.

Can care for themselves, but might need more instruction and support than the typical person.

Many can live in independent situations, but some need the support of a group home.



3-4% of those with ID

IQ 20 to 34

Considerable delays in development

Understands speech, but little ability to communicate

Able to learn daily routines

May learn very simple self-care

Can only communicate on the most basic levels.

Needs direct supervision in social situations

Cannot perform all self-care activities independently and need daily supervision and support.

Most in this category cannot successfully live an independent life and will need to live in a group home setting.


1-2% of those with ID

IQ less than 20

Significant developmental delays in all areas

Obvious physical and congenital abnormalities

Extremely limited communication ability.

May respond to physical and social activities

Requires close supervision; require 24/7 support and care.

Requires attendant to help in self-care activities

Not capable of independent living

Depend on others for all aspects of day-to-day life

Frequently have other physical limitations as well.

Differential Diagnosis of Intellectual Disability: DSM-5 Differential

  • Communication disorders

Individuals who have troubles communicating may appear to have ID upon first meeting

However, those with communication disorders alone do not show deficits in intellectual and adaptive behavior.

Other individuals may have both ID plus communication disorder(s)

  • Specific learning disorder (SLD)

Individuals with specific learning disorder will have problems in one area of learning, but normal learning in others.

Do not show deficits in intellectual and adaptive behavior.

Can co-occur with ID

  • Autism spectrum disorder (ASD)

Are there troubles with social communication? E.g. is communication two way, or is it one way (i.e. impairment with reciprocal communication)?

Are there restricted interests or activities?


Differential Diagnosis of Intellectual Disability: Medical Causes

Consider the following in those with otherwise unexplained developmental delay or intellectual disability:


Is there maternal history of alcohol consumption during pregnancy?

Facial dysmorphisms?

Neuropsychiatric problems such as problems with learning, language, ADHD symptoms, sensory issues?

Consider fetal alcohol spectrum disorder (FASD)

For more information

Any of the following physical signs?

  • Decreased or poor muscle tone
  • Short neck, with excess skin at the back of the neck
  • Flattened facial profile and nose
  • Small head, ears, and mouth
  • Upward slanting eyes, often with a skin fold that comes out from the upper eyelid and covers the inner corner of the eye
  • White spots on the colored part of the eye (called Brushfield spots)
  • Wide, short hands with short fingers
  • A single, deep, crease across the palm of the hand
  • A deep groove between the first and second toes

Any of the following cognitive or behavioural signs?

  • Troubles with attention, behaviour, learning, delayed language or speech?

Consider Down Syndrome

For more information

Any of the following physical features?

  • Large head circumference, long face, prominent forehead, large ears, and prominent jaw.

Any of the following medical issues?

  • Seizures (seen in 25% of those with Fragile X)

Any of the following psychiatric symptoms?

  • Intellectual disability
  • Hyperactivity / ADHD,
  • Autistic behaviours,
  • Sensory problems,
  • Anxiety / social anxiety
  • Speech delays, or perseverative speech?

Consider Fragile X, the most common single-gene cause of hereditary mental retardation.

For more information

Any of the following behaviours?

  • Extreme food seeking behaviours (Hyperphagia),

Any of the following physical features?

  • Obesity,
  • Hypotonia
  • Small hands/feet
  • Short stature,scoliosis
  • Microorchidism (i.e. small testes in males)
  • Fair hair/light skin
  • Almond shaped eyes
  • Sleep apnea

Any of the following psychiatric symptoms?

  • Obsessions and compulsions
  • Cognitive rigidity, i.e. stubborn, inflexible, needing sameness
  • Behavior problems: aggression, temper tantrums, emotional lability, daytime sleepiness

Consider Prader Willi

Any of the following?

  • Lower social activity, poor social coping skills, increased immaturity,
  • Hyperactivity/impulsivity
  • Higher anxiety, shyness, depression, lower self-esteem

Any of the following physical features?

  • Short stature,
  • Webbed neck,
  • Cardiac abnormalities,
  • Thyroid disease,
  • Hearing loss. (heterogeneous)

Any of the following cognitive features?

  • Generall normal intellectual function;
  • Verbal skills better than nonverbal skills;
  • Visuospatial deficits

Consider Turner Syndrome



People with ID are at a higher risk of having numerous conditions (Oeseburg et al., 2011) such as:


Medical isssues

  • Epilepsy (22%)
  • Cerebral palsy (20%)
    • Alzheimer’s disease (particularly in those with Down Syndrome) 


Psychiatric (and neuropsychiatric) conditions

  • Anxiety disorder (17%)
Any problems with worrying too much?
  • ADHD (9-18%)
Any problems paying attention? Any troubles acting before thinking?
  • Autistic disorder (10%)
Any problems seeing things from other's perspectives?
  • Depressive and bipolar disorders
Any problems with depressed mood?
  • Anxiety disorders
Any problems with anxiety?
  • Developmental coordination disorder (DCD)

Are there problems with fine motor skills? Gross motor skills?

  • Sensory processing problems

Usually present with ASD, but can also co-occur with ADHD, learning disabilities, FASD and other conditions

Can occur with multiple conditions

Are there sensitivities to sensory input, e.g. auditory, tactile, olfactory, visual? Or abnormal responses to sensory input?



Has a psychoeducational assessment been done, with full-scale IQ?

  • If not, then refer to psychology for psychoeducational assessment.

Psychoeducational Assessment

Does child have unexplained MR/DD, even in the ab-sence of dysmorphic facial features, other clinical features or positive family history.” (Shaffer, 2005)

Psychoeducational assessment

Refer to genetics (Shaffer, 2005)

Is there a possibility of metabolic condition?

Refer to pediatrics who can consider metabolic screening

Any structural differences noted, e.g. microcephaly, macrocephaly? Any neurologic symptoms (e.g. spasticity, ataxia, dystonia, seizures, loss of motor skills, abnormal reflexes)

Refer to neurology

Consider neuroimaging

Is there possible seizure disorder?

Refer for EEG

Are there any medical issues suspected? (E.g. hypothyroidism)

Do testing as indicated


Management / Treatment


  • When providing education to the individual with ID about conditions or other issues, use appropriate resources targeted for those with ID such as
    • Easy Health (from the UK) has a wide range of handouts on various topics including healthy living, as well as anxiety, depression, and autism.


  • Attending school is essential for individuals with ID to learn academics as well as life skills; most school boards have specialized programs for those with ID.
  • Recommendation
    • Liaise with the school.
    • Ensure that the student with ID has an IEP in place, as well as appropriate support, such as educational assistant (EA), or specialized classroom.
    • Those with mild ID tend to be integrated in the mainstream school setting, whereas those with severe ID will likely be in a specialized classroom.

Occupational therapy (OT) and physiotherapy (PT)

  • Are there ongoing sensory / motor / self-regulation issues?
    • Occupational therapy (OT) can help, as well as with day-to-day function at home and school, such as life skills.
    • Physiotherapists (PT) can help with motor issues such as low muscle tone, problems with coordination.

Speech language therapy (SLP)

  • Are there difficulties with communication?
    • SLP may help improve the ability to communicate (Wilkinson, 2007).

Service Navigation

  • Ensure that the family is connected to community organizations that support those with intellectual disabilities (and their families), such as a case worker.

Healthy activities for a sense of connection, belonging and purpose

  • Persons with ID may benefit from the usual activities for others such as sports and recreational activities; spiritual-based activities, etc.
  • Persons with more severe ID may need more specific services geared to those with ID.

Family Support

  • What are the family’s needs?
    • Information / knowledge about the diagnosis, or related issues
    • Emotional support
    • Help with practical issues, e.g. finances
    • Peer support with other families?

Sleep Challenges

Are there problems with sleep?

  • Start with sleep hygiene and behavioural strategies including limiting screen time 1-2 hrs before bedtime 

Are there still problems with sleep? 

  • Consider melatonin, which has been specifically studied in people with autism and shown considerable benefit (Cortese, Wang, Angriman, Masi & Bruni, 2020)
  • Note: 
    • Off-label use of antipsychotics for sleep issues is common but unfortunately not evidence-based 
    • The American Academy of Child & Adolescent Psychiatry (Findling, Drury, Jensen, Rapoport, & AACAP Committee on Quality Issues, 2011) recommends AGAINST the usage of antipsychotics for sleep.

Behaviours that Challenge (BTC)

Behaviours that challenge (BTC) (aka challenging behaviour) include:

  • Self-injurious behaviour
  • Anger, aggression, irritability
  • Property destruction
  • Pica


  • Understand what is beneath the challenging behaviour, as there may be many different causes for the behaviour such as:
    • Health related reasons, e.g. pain; constipation.
    • The person is sensory overloaded (e.g. too much sound)
    • The person is reacting to stressful life circumstances such as a loss or change (e.g. change in caregiver)
    • The person is aggressive because they do not yet have the skills to express their feelings or wishes in a more appropriate way, e.g. not yet able to express that they are frustrated, sad, angry, anxious.
    • Mental health related reason, e.g. depression, anxiety, adjustment problems

Management of challenging behaviour (CB)

  • Address the underlying cause (rather than simply using positive/negative reinforcement strategy for the behaviour)
    • Example
      • If the person is aggressive because they are constipated, it will be more effective deal with their constipation (as opposed to punish them for being aggressive).
  • Consider referral to behaviorist if available
    • Behaviorists uses multiple interventions including
      • Functional assessment
      • Antecedent-behaviour-consequence (ABC) charts
  • Are there challenging behaviours that persist despite exhausting non-medication strategies? Is the severity sufficient to warrant medication trial? (e.g. person at risk of losing their placement or housing, etc.)
    • Options
      • Second generation antipsychotics for problem behaviours (Snyder, 2002)
        • Note a lack of evidence for medications in ID, and thus, much evidence is extrapolated from studies in those with ASD. 
        • Start low and go slow -- people with ID generally have more comorbid medical issues, and may be more sensitive to side effects
        • Antipsychotic medications appear to be effective in the short-term, though they carry significant side effects (McQuire C et al., 2015).
      • Is there comorbid ADHD?
        • Consider stimulant medication for ADHD 
          • Evidence for the use of methylphenidate first-line for ADHD with comorbid ID -- note lower effect size than in children with ADHD and average intelligence (Arnold, 2013). 
          • First-line
            • Methylphenidate, given that
              • More evidence for methylphenidate (than amphetamine) for ADHD in the context of ASD (Mahajan et al., 2012; Rodrigues et al. [in press]) and ID (Arnold, 2013)
              • Methylphenidate is better tolerated (than amphetamine) in children and adolescents (Cortese et al., 2018)
          • Watch for paradoxical effects such as worsening behaviours, irritability and insomnia (DeFlllipis & Wagner, 2016)
      • Is there self-injurious behaviour?
        • Consider Naltrexone (Revia)
      • Are there mood/anxiety issues?
        • Consider SSRIs

Antipsychotic Medication Table for Adolescents and Adults




Aripiprazole* (Abilify™)

Start 5-10 mg daily

Target 5-30 mg daily


Felt to have less side effects (less metabolic effects, less prolactinemia) than other medications
Some evidence suggests equivalent to Risperidone in irritability/aggression for autism (Lamberti et al., 2016)  

Risperidone (Risperdal ™)

  • Tablets
  • Liquid

Start at 0.25-0.5 mg daily

Target 1-4 mg daily

Risperidone dosage of 1-2 mg/daily shown to be most beneficial for irritability / aggression in children with autism (Lamberti et al., 2016).

Olanzapine (Zyprexa™)

Olanzapine (Zydis ™) (rapid dissolve)

Start 2.5-5 mg daily

Increase 2.5-5 mg daily in weekly intervals up to target dosage

Initial therapeutic target 10 mg daily

Max 20 mg daily

Compared to Risperidone, lower risk of motor side effects and elevated prolactin but higher risk of sedation and weight gain

Quetiapine IR (Seroquel™)


Immediate-release tablet (IR):

Day 1: 25 mg twice daily

Day 2: 50 mg twice daily

Day 3: 100 mg twice daily

Day 4: 150 mg twice daily

Day 5: 200 mg twice daily target dosage

Usual dosage range: 200 to 400 mg twice daily

Maximum daily dose: 800 mg/day.

Studies show no additional benefit was seen with 400 mg twice daily vs 200 mg twice daily.

Quetiapine XL (Seroquel XL)

Day 1: 50 mg once daily

Day 2: 100 mg once daily

Day 3: 200 mg daily

Day 4: 300 mg daily

Day 5: 400 mg once daily

Usual dosage range: 400-800 mg once daily

Max daily dose: 800 mg/day.


Ziprasidone (Geodon™)


Start 20 mg daily

Target 20-160 mg daily





  • CAMESA Monitoring Guidelines recommend: 
    • Height, weight, waist circumference, blood pressure
    • Bloodwork: fasting plasma glucose, insulin, total cholesterol, LDL, HDL, triglycerides, prolactin. 
  • Ideally, values are monitored at baseline, three months, six months, and every six months thereafter (Pringsheim, Panagiotopoulos, Davidson, Ho & CAMESA guideline group, 2011).

Capacity and Consent in Emerging Adults with Intellectual Disability

With children/youth with intellectual disabilities, ensure that informed consent is obtained for any interventions especially medications.

  • Discuss risks, benefits, and alternative treatments with parents (and ideally, the child/youth is providing assent).

As children become youth and emerging adults however, they may make increasingly assert their autonomy and also decisions that their parents disagree with, e.g. a youth with intellectual disability who wants to stop taking necessary medications; who wants to date an older boyfriend and move out with him, etc.

For more information about capacity and consent in emerging adults with developmental disabilities 

Outcome / Prognosis of Intellectual Disability

High mortality rates

  • Individuals with severe/profound ID have higher mortality rates because of complications associated with physical disease.
  • Accidental injury rates may be increased due to lack of awareness of risk/danger.
  • There is increased risk for suicide, presumably because life is more challenging and difficult for them.

Victimization by others

  • Gullibility and lack of awareness of risk may result in exploitation by others, victimization, fraud, unintentional criminal involvement, false confessions, risk for physical/sexual abuse.

Outcomes vary, depending on the severity of the intellectual disability. One estimate is the following:








50-55 to 70

35-40 to 50-55

20-25 to 35-40

<20 or 25

Age at death (years)




About 20

% of population with ID





Academic level achieved by adulthood

Gr. 6

Gr. 2

Below Gr. 1

Below Gr. 1

Placement / residence

May be able to live in community with supports

Likely needs sheltered placement

Requires highly structured, supervised setting

Requires highly structured, supervised setting


Clinical Practice Guidelines

Shaffer L: American College of Medical Genetics guideline on the cytogenetic evaluation of the individual with developmental delay or mental retardation,

Nov/Dec 2005, Genetics in Medicine 7(9):650-654.


Szymanski L, King B: Practice parameters for the assessment and treatment of children, adolescents, and adults with mental retardation and comorbid mental disorders, JAACAP, Dec 1999, 38(12): 5S-31S (supplement).

NOTE - these Practice Parameters are out of date, but are provided for historical information.


Sullivan W et al.: Primary care of adults with intellectual and developmental disabilities

2018 Canadian consensus guidelines. Canadian Family Physician, 64: Apr 2018.


Kishore M et al.: Clinical Practice Guidelines for Assessment and Management of intellectual disability. Indian J Psychiatry. 2019 Jan; 61(Suppl 2): 194–210.

doi: 10.4103/psychiatry.IndianJPsychiatry_507_18

Resources for Clinicians

Kelly M. Communicating effectively with people with developmental disabilities. In: Sullivan WF, Developmental Disabilities Primary Care Initiative Scientific and Editorial Staff, editors. Tools for the primary care of people with developmental disabilities. Toronto, ON: Surrey Place Centre, MUMS Guidelines Clearinghouse; 2011. p. 18-20. .

Website with an interactive tool for the clinician and scientist, both expert and trainee, in order to identify 81 treatable causes of intellectual disability. Based on a systematic literature review published in “Molecular Genetics and Metabolism” in Mar 2012.


Marrus N, Hall L. Intellectual Disability and Language Disorder. Child Adolesc Psychiatr Clin N Am. 2017;26(3):539–554. doi:10.1016/j.chc.2017.03.001


Arnold, L. E. (2013). Commentary: Filling out the evidence base for treatment of attention-deficit hyperactivity disorder symptoms in children with intellectual and developmental disability: conclusions for clinicians—a response to Simonoff et al. (2013). Journal of Child Psychology and Psychiatry, 54(6), 701-703. doi: 10.1111/jcpp.12097

Curry CJ, Stevenson RE, Aughton D, Byrne J, et al. Evaluation of mental retardation: Recommendations of a Consensus Conference: American College of Medical Ge- netics. Am J Med Genet 1997;72:468–477.

DeFilippis, M., & Wagner, K. D. (2016). Treatment of autism spectrum disorder in children and adolescents. Psychopharmacology Bulletin, 46(2), 18-41.

Ke X, Liu J. Intellectual disability. In Rey JM (ed), IACAPAP e-Textbook of Child and Adolescent Mental Health. Geneva: International Association for Child and Adolescent Psychiatry and Allied Professions 2012.


Kelly M. Communicating effectively with people with developmental disabilities. In: Sullivan WF, Developmental Disabilities Primary Care Initiative Scientific and Editorial Staff, editors. Tools for the primary care of people with developmental disabilities. Toronto, ON: Surrey Place Centre, MUMS Guidelines Clearinghouse; 2011. p. 18-20. Available from: . Accessed 2019 Oct 14.

Lamberti, M., Siracusano, R., Italiano, D., Alosi, N., Cucinotta, F., Di Rosa, G., ... & Gagliano, A. (2016). Head-to-Head Comparison of Aripiprazole and Risperidone in the Treatment of ADHD Symptoms in Children with Autistic Spectrum Disorder and ADHD: A Pilot, Open-Label, Randomized Controlled Study. Pediatric Drugs, 18(4), 319-329. doi: 10.1007/s40272-016-0183-3.

Results: Aripiprazole and risperidone appeared to have similar benefits with efficacy and tolerability; prolactin levels decreased in aripiprazole compared to risperidone.

McQuire C, Hassiotis A, Harrison B, Pilling S: Pharmacological interventions for challenging behaviour in children with intellectual disabilities: a systematic review and meta-analysis, BMC Psychiatry, 2015 Nov.


Nash A, Davis L: Fetal Alcohol Spectrum Disorders: What pediatric providers need to know. J Pediatr Health Care. 2017 Sep-Oct; 31(5): 594-606. Doi: 10.1016/j.pedhc.2017.04.002.

Pringsheim, T., Panagiotopoulos, C., Davidson, J., Ho, J. & Canadian Alliance for Monitoring Effectiveness and Safety of Antipsychotics in Children (CAMESA) guideline group. (2011). Evidence-based recommendations for monitoring safety of second-generation antipsychotics in children and youth. Paediatrics & Child Health,

16(9), 581-589. doi: 10.1093/pch/16.9.581.


Oeseburg B, Dijkstra GJ, Groothoff JW et al (2011). Prevalence of chronic health conditions in children with intellectual disability: a systematic literature review. Intellectual and Developmental Disabilities, 49:59-85.


Snyder R, Turgay A, Aman M et al (2002). Effects of risperidone on conduct and disruptive behavior disorders in children with subaverage IQs. Journal of the American Academy of Child & Adolescent Psychiatry, 41:1026- 1036.


Sullivan W et al.: Primary care of adults with intellectual and developmental disabilities 2018 Canadian consensus guidelines. Canadian Family Physician, 64: Apr 2018.


Vedi K, Bernard S: The mental health needs of children and adolescents with learning disabilities Curr Opin Psychiatry, 2012, 25-353-358.


Wilkinson KM, Hennig S (2007). The state of research and practice in augmentative and alternative communication for children with developmental/ intellectual disabilities. Mental Retardation and Developmental Disabilities Research Reviews, 13:58-69.


Written by the child psychiatrists at CHEO at uOttawa. 

Conflicts of Interest: No competing interests declared.


This information is offered ‘as is' and is meant only to provide general information that supplements, but does not replace the information from a qualified expert or health professional. Always contact a qualified expert or health professional for further information in your specific situation or circumstance.

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Date Posted: Feb 20, 2020
Date of Last Revision: Jul 8, 2022

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