Adult ADHD – What do we know and why should you care?

Dr Helen Read 20 May 2024

Adult ADHD – What do we know and why should you care?

I became passionate about attention deficit hyperactivity disorder (ADHD) after my eldest son, then aged 3, was diagnosed with autism spectrum disorder (ASD) and subsequently ADHD 21 years ago. Since then, my youngest son now aged 10 has also received ASD/ADHD diagnoses. In 2020 I received my own ADHD diagnosis, although I have been on stimulant medication for the past ten years or so (started for a sleep disorder) which I now know to have been related to my ADHD. So, you might say that ADHD has been a big part of my adult life, and parenting experience.

It is fair to say that, although there has been immense goodwill and desire to help from services, I became an expert initially after navigating my children’s difficult journeys through diagnosis, treatment and support in the medical and education systems. The journey has not been easy, but it has been very successful, and I am passionate about talking about ADHD, particularly to medical colleagues, to improve our experiences and those of our patients.

Many doctors and colleagues feel inadequately prepared, and therefore anxious about adult ADHD.  When I was at medical school in the late 80s, adult ADHD really wasn’t a thing; the small amount we did learn was within learning disabilities, and regarding children.  I don’t think this has changed much in the decades since.

There is a lot of misinformation about ADHD out there. False beliefs are widespread in the general population and in the medical literature. I believe that this may be due to some of the counter intuitive aspects of ADHD, and the sad truth that many of the symptoms are more commonly conceptualised as moral or character failings, or due to lack of will power.

As doctors, this is not good enough for us. So, with our patients relying on us to give them accurate information and help them when it is right and reasonable to do so, where can we turn for information we can trust?

Two decades ago, an international team of scientists published the first International Consensus Statement on attention deficit hyperactivity disorder (ADHD) 1. They sought to present the wealth of scientific data attesting to the validity of ADHD as a mental disorder and to correct misconceptions about the disorder that stigmatised affected people, reduced the credibility of health care providers, and prevented or delayed treatment of individuals challenged by the disorder. Clearly, despite the impeccable credentials and international reputations of the authors, the message did not make it through to most of us; and 2002 is now a long time ago…

To the rescue comes this updated International Consensus statement cataloguing important scientific discoveries from the last 20 years. Rather than ‘an encyclopaedia of ADHD’ or diagnosis and treatment guidelines, which can be found in the references, their aim is to challenge misconceptions and provide current and accurate information about ADHD supported by a substantial and rigorous body of evidence.  They curated findings with a strong evidence base from published high quality meta-analyses or large registry studies with >2000 participants. Meta-analyses needed to report data from 5 or more studies or 2000 or more participants. 208 empirically supported firm statements about ADHD in terms of nature, causes, course, outcomes and treatments can be made.

The diagnosis of ADHD has been criticised as being subjective because it is not based on a biological test. This criticism is unfounded, as ADHD meets standard criteria for validity of a mental disorder established by Robins and Guze 2 , elaborated by Faraone 3 (see box)

The disorder is considered valid because:

  1. well-trained professionals in a variety of settings and cultures agree on its presence or absence using well-defined criteria and
  2. the diagnosis is useful for predicting
  1. additional problems the patient may have (e.g., difficulties learning in school);
  2. future patient outcomes (e.g., risk for future drug abuse)
  3. response to treatment (e.g., medications and psychological treatments); and
  4. features that indicate a consistent set of causes for the disorder (e.g., findings from genetics or brain imaging)
Professional associations have endorsed and published guidelines for diagnosing ADHD. Main required features:1)     the presence of developmentally inappropriate levels of hyperactive-impulsive and/or inattentive symptoms for at least 6 months;2)     symptoms occurring in different settings (e.g., home and school);

3)     symptoms that cause impairments in living;

4)     some of the symptoms and impairments first occurred in early to mid-childhood; and

5)     no other disorder better explains the symptoms

And as with all other diagnoses, of course, ADHD diagnosis should be made by a licensed clinician

ADHD occurs throughout the developed and developing world and is more common in males compared with females. It has not become more common over the past three decades although due to increased recognition by clinicians, the disorder is more likely to be diagnosed today than in prior decades.

In adolescence and young adulthood, many individuals with a history of childhood ADHD continue to be impaired by the disorder, although they often show reduced hyperactivity and impulsivity while retaining symptoms of inattention. ADHD impairs the functioning of highly intelligent people, so the disorder can be diagnosed in this group.

For most people with ADHD, many genetic and environmental risk factors accumulate to cause the disorder. The environmental risks for ADHD exert their effects very early in life, during the fetal or early postnatal period.

Many large epidemiologic and clinical studies show that genetic and environmental influences are partially shared between ADHD and many other psychiatric disorders (e.g. schizophrenia, depression, bipolar disorder, autism spectrum disorder, conduct disorder, eating disorders, and substance use disorders) and with somatic disorders (e.g. migraine and obesity). Evidence of shared genetic and environmental risks among disorders suggest that these disorders also share a pathophysiology in the biological pathways that dysregulate neurodevelopment and create brain variations leading to disorder onset. ADHD often co-occurs with other psychiatric disorders, especially depression, bipolar disorder, autism spectrum disorders, anxiety disorders, oppositional defiant disorder, conduct disorder, eating disorders, and substance use disorders.  Their presence does not rule out a diagnosis of ADHD.

Genetic studies confirm a polygenic cause for most cases of ADHD. The polygenic risk for ADHD predicts ADHD symptoms in the population, suggesting that the genetic causes of ADHD as a disorder also influence sub-threshold levels of ADHD symptoms in the population

Some environmental correlates of ADHD have strong evidence for a causal role but, for most, the possibility remains that these associations are due to correlated genetic and environmental effects. For this reason, features of the pre and post-natal environments that increase risk for ADHD should be referred to as correlates, rather than causes. These include:

  • Exposure to toxicants e.g., lead.
  • Nutrient deficiencies – ferritin, Vit D, omega 3.
  • Events during pregnancy and birth: prematurity/low birth weight, pre-eclampsia, obese mums, thyroid over and under, number of miscarriages.
  • Deprivation, stress, infection, poverty and trauma.
  • Smoking in pregnancy increases risk by >50% but excess disappears when adjusted for family history i.e., association is shared risk not cause.

People with ADHD often show impaired performance on psychological tests of brain functioning, but these tests show insufficient reliability or difference for diagnosis. In terms of brain differences found by neuroimaging studies, again nothing stands out as demonstrably different. The differences seen in children were not seen in adolescents or adults 4,5. All the differences observed were small to very small and subtle.

Adverse outcomes from untreated ADHD

Untreated ADHD is a disorder which could be associated with serious distress and/or impairments in living.

A meta-analysis found that, compared with typically developing people, children and adolescents with unmedicated ADHD were about 20 % more likely to be overweight or obese (15 studies, over 400,000 participants), and adults with unmedicated ADHD almost 50 % more likely to be overweight or obese (9 studies, over 45,000 participants) 6. Meta-analyses of twelve studies with over 180,000 participants found that people with unmedicated ADHD were about 40 % more likely to be obese, whereas those who were medicated were indistinguishable from typically developing people.

A meta-analysis of seven studies with over 5000 youths and their parents reported large impairments in the quality of life of youths with ADHD relative to typically developing peers, regardless of whether evaluated by the youths themselves or by their parents. Physical functioning was only moderately impaired, but emotional functioning and social functioning was strongly impaired. School functioning was strongly impaired. As youths with ADHD grew older, their quality of life compared with typically developing peers grew worse in physical, emotional, and school domains. A meta-analysis of 22 studies with over 21,000 participants found that youths with ADHD were strongly impaired in the ability to modulate their reactivity to novel or stressful events 7. Another meta-analysis, combining twelve studies with over 1900 participants, found that adults with ADHD had very elevated levels of emotional dysregulation compared with normally developing controls.

  • Regulatory agencies deem ADHD medications safe and effective for reducing ADHD symptoms of ADHD.
  • Adverse effects of ADHD medications are typically mild. If severe, change dose or medication.
  • Stimulant medications for ADHD are more effective than non-stimulants, but have more risk of diversion, misuse, and abuse.
  • Non-medication ADHD treatments are less effective than medication treatments but are useful to help problems that remain after medication is optimised.

A meta-analysis of five studies with over 43,000 children and adolescents found no significant difference in adverse cardiac events between methylphenidate and atomoxetine, and a meta-analysis of three studies with 775 adults found no significant difference in adverse cardiac events between methylphenidate and placebo. 8 A meta-analysis covering people of all ages reported methylphenidate was not associated with a higher risk of all-cause death (3 studies, over 1.4 million people), heart attack or stroke (3 studies, over half a million people). 9  A Swedish registry study of over 23,000 adolescents and young adults treated with methylphenidate for ADHD found no evidence for an association between psychosis and methylphenidate treatment. A year after initiation of methylphenidate treatment, the incidence of psychotic events was 36 % lower in those with a history of psychosis and 18 % lower in those without a history of psychosis relative to the period immediately before the beginning of treatment 10.

What is the economic burden of ADHD?

Given the many adverse outcomes associated with ADHD, it will come as no surprise that these effects have a substantial economic cost to individual patients, families, and society.

A systematic review of 19 U.S. studies of hundreds of thousands of people found that ADHD was associated with overall national annual costs from $143 to $266 billion, mostly associated with adults ($105 to $194 billion). Costs borne by family members of people with ADHD ranged from $33 – $43 billion 11.

German health insurance records, including over 25,000 patients with ADHD, indicate that patients with ADHD cost roughly €1500 more annually than those without ADHD. Main cost drivers were inpatient care, psychiatrists, and psychotherapists. Mood, anxiety, substance use disorders, and obesity were significantly more frequent in patients with ADHD. The additional costs resulting from these conditions added as much as €2800 per patient 12.

The Hong Kong Clinical Data Analysis & Reporting System, a population-based, electronic medical records database, was used to examine over 25,000 people receiving methylphenidate for ADHD. During the 90-day period prior to initiation of treatment, individuals with ADHD were over six times more likely to attempt suicide than after treatment. After ongoing treatment, the risk for attempted suicide was no longer elevated among patients with ADHD 13.

Using a database that tracks more than sixty German nationwide health insurance programs, a study of five million member records identified 2,380 individuals first diagnosed with ADHD as adults. Their direct healthcare costs in the year following diagnosis averaged €4,000. Despite explicit German guidelines recommending ADHD medication, only a third were prescribed medication, dropping to one-eighth four years later. Two-thirds received psychotherapy. The authors concluded that “guideline recommendations are not yet comprehensively implemented in everyday routine care” 14.

New directions for diagnosis

·         To better understand the nature and causes of emotional symptoms in ADHD and whether these should be incorporated into diagnostic criteria 15.

·         To determine if and how mild or sub-threshold cases of ADHD should be diagnosed and treated 16.

·         Different trajectories of ADHD in different populations and across the life-cycle need to be further investigated.

·         Stigmatising attitudes toward ADHD are common and may play a role in socially and clinically important outcomes. These negative attitudes affect patients at all stages of their life. Such attitudes have been documented among individuals at all ages and in all groups, including family, peers, teachers, clinicians, and even individuals with ADHD themselves 17.

Despite these and other gaps in our knowledge about ADHD, nearly two and a half centuries after the first textbook description of an ADHD-like syndrome, we can be confident that 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.

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