Critiquing the evidence behind “evidence-based conclusions” about ADHD

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Attention-deficit hyperactivity disorder (ADHD) is a hot topic. In 2021 alone, the National Elf Service hosted blogs on; the safety of ADHD medications (De Crescenzo, 2021), drug treatment of ADHD in individuals with co-existing autistic spectrum disorder (ASD) (Badenoch 2021), service provision for people with ADHD in Ireland (Ellis Logan 2021), and the risk of violence for people with ADHD (Schwartz 2021). Despite the increasing awareness – or possibly because of it – the controversies and misconceptions around the disorder persist. This may partially explain the stigma attached to the diagnostic label (Kundert 2022).

Led by Stephen V Faraone, the World Federation of ADHD – the organisation whose primary aim is to “disseminate education about ADHD and advocate for patients and their families by enabling world experts to teach clinicians, researchers and other ADHD stakeholders on how to use scientific facts and clinical wisdom to create better outcomes for people with ADHD” – set out to challenge the misconceptions by curating findings on ADHD with solid evidence in their Consensus Statement (Faraone et al, 2021).

ADHD is a hot topic – the authors of this consensus statement set out to challenge the misconceptions that surround ADHD.

Methods

The authors identified strong evidence as follows:

Large cohort studies
- Including more than 2,000 participants
Meta-analyses
- Including at least five studies or 2,000 participants
- Excluding studies that did not assess publication bias
- Excluding results from treatment studies comparing to waiting-list or treatment as usual
Network meta-analyses
- Including adjusted funnel analysis

The magnitude of effect size was defined as follows:

Small effect: generally difficult to observe in an individual but may be very important for public health if it concerns a common exposure
- Standardised mean difference or 0.20, or
- Correlation coefficient of 0.10
Medium effect: expected to be noticeable to a careful observer
- Standardised mean difference or 0.50, or
- Correlation coefficient of 0.24
Large effect: generally relevant to clinical practice at the level of the individual
- Standardised mean difference or 0.80, or
- Correlation coefficient of 0.37

Results

The authors generated 208 statements about ADHD using the search strategy with published evidence. These statements were subsequently approved by 366 people (described as additional colleagues who were invited to join as signatories to indicate their support of the document) who have read the document.

In sum, they found that:

ADHD is not a new disorder – clinical reports date back as far as 1775
ADHD diagnosis, when formulated by a licenced clinician, is valid
The prevalence of ADHD:
- is more common in males than females,
- does not differ between different continents,
- is lower in adults than youth with the rate reducing with increasing age,
- has not changed (in children and adolescents) over the past three decades, but the clinical diagnosis is more likely to be given in more recent years due to increased recognition by clinicians
Most cases of ADHD are caused by the combined effects of genetic and environmental risk factors
Formal psychological tests and neuroimaging tests might be supportive but not at all definitive in diagnosing ADHD
People with ADHD are at increased risk of many physical conditions, including obesity and asthma
People with ADHD are at increased risk of distress and impairment in living, including reduced quality of life, increased rates of suicide, death by homicide and unintentional injury, as well as increased rates of incarceration and educational underachievement
The economic burden of ADHD is estimated to be substantial worldwide (e.g. estimated total annual costs of over 20 billion dollars in Australia, and more than one billion euros in the Netherland)
Medication treatments for ADHD are safe, effective, and mostly well-tolerated
- Stimulant medications were more effective than non-stimulants
- Stimulant medications were more liked to be diverted, misused and abused
Non-medication treatments – including behavioural and cognitive behavioural therapy as well as supplement, diet, and exercise – showed mixed benefits/findings.

This Consensus Statement provides a comprehensive summary of existing research evidence on ADHD.

Conclusions

The authors concluded:

“the contemporary diagnosis of the disorder is a valid and useful category that can be used around the world to improve the lives of the many people who suffer from the disorder and its complications.”

“the contemporary diagnosis of ADHD is a valid and useful category that can be used around the world to improve the lives of the many people who suffer from the disorder and its complications.”

Strengths and limitations

Despite explicitly stating at the start that the authors did not intend to present an encyclopaedia of ADHD, they kind of did. The Consensus Statement is a comprehensive summary of existing research evidence on ADHD.

That said, as with many summaries/reviews, the quality of the Consensus Statement is only as good as the existing research evidence on ADHD. As the authors outline in the discussion, there’s much more we need to explore about ADHD such as:

Cultural effects on the expression of ADHD
Gender differences in ADHD
ADHD in adults
Different trajectories of ADHD across the life-cycle
Stigma and ADHD.

Notwithstanding these limitations, we are impressed with both the breadth and depth of the Consensus Statement. We recommend it as a starting document for anyone interested in learning about ADHD.

The quality of the Consensus Statement is only as good as the existing research evidence on ADHD and more evidence is needed on issues such as the cultural, gender and age differences that exist in ADHD.

Implications for practice

In addition to the areas of further research outlined by the authors above, we feel that the following areas are worth exploring further:

Is there such a thing as adult onset ADHD (where the onset of symptoms is in adulthood)? If so, how do we best conceptualise the condition and formulate treatment?
Do medications work because they treat the underlying disease specific to ADHD or because they reduce the non-specific symptoms associated with ADHD (e.g. inattention and cognitive difficulties)?
Given the high rate of ADHD among Black youth in the United States, what is the prevalence of ADHD among other minority racial groups worldwide (e.g. Māori in New Zealand, and Indigenous peoples in Australia)?
Considering the above questions, what impact do social determinants of health have on diagnosing and managing ADHD?

The fourth and final point, the role of societal influences on ADHD, is crucial for research and clinical practice moving forward.

For example, based on the findings from 19 studies in 13 countries, Whitely et al. (2018) proposed the “late birthdate effect” of ADHD, where the youngest children in a school year were significantly more likely to be diagnosed with ADHD compared to older classmates. Thus, instead of rushing to be diagnosed and medicated, the authors argued, these young-for-grade children should be supported through the extra time they need to mature.

Similarly, in adults, Pai and Vella (2022) noticed a significant rise in referral rates for ADHD assessment during the COVID-19 lockdown. They speculated possible factors including the isolation enforced by the lockdown and associated stress and frustration, as well as the influence of the mainstream media and increased public awareness. In particular, they wondered if: “media attention may have lowered what was previously thought to be a clinical threshold requiring further assessment.”

While the Consent Statement insists that the rate of ADHD has not changed over the past three decades, it also acknowledges that the disorder is more likely to be diagnosed today than at any stage in the past. This rise in the diagnosed prevalence is attributed to increased awareness and recognition. Is it possible, however, that the diagnosed prevalence reflects a change in the threshold – both in the diagnostic criteria we use and the societal expectations we are under – of what is accepted as a mental disorder and what is expected as age-related immaturity?

The boundary between what is normal and abnormal is often vague and blurred in psychiatry. Diagnostic criteria for ADHD may be valid, but they are merely a series of behavioural descriptions. Multiple factors likely impact different people in different ways and if we rely too much on the biomedical model (i.e. diagnose and treat), we may miss many opportunities to intervene. The psychosocial context is often critical and, if appropriate services exist, a good starting point for ADHD management.

Societal influences on the cause, diagnosis and effect of ADHD are difficult to pinpoint, but are likely to have an important role. As we explore these factors further, we may discover innovative ways to improve the lives of people living with ADHD at different layers and levels – from the population level to the individual level through educational, justice and government organisations, in addition to health care providers.