ADHD, Autism, Eating Disorders, PTSD, and OCD

TL;DR. Five conditions that between them affect a large share of the population and that Chapter 41 and Chapter 42 did not cover. ADHD is a disorder of the brain's executive control system, not of attention as such, and stimulants calm rather than excite people who have it for a reason that makes mechanical sense. Autism is a difference in how the brain processes social information and sensory input, is highly heritable, and is emphatically not caused by vaccines, a claim traced to a retracted and fraudulent paper. Anorexia nervosa has the highest mortality of any psychiatric disorder. PTSD has genuinely effective trauma-focused treatments that most sufferers never receive. And OCD is not tidiness; it is a torment of intrusive thoughts and rituals, and its specific treatment works.

Key takeaways

• ADHD affects roughly 5 to 7 percent of children and about 2.5 to 3 percent of adults, and untreated it carries measurable risks: accidents, substance use, unemployment, and premature death.
• Stimulants work in ADHD by increasing signalling in an under-active control network, which is why they improve focus rather than causing agitation in people who have it.
• The MMR-autism claim came from a 1998 paper that was retracted, whose author was struck off the medical register, and it has been contradicted by studies covering millions of children.
• Anorexia nervosa kills roughly 5 to 10 percent of those affected, from both medical complications and suicide, and early treatment substantially improves outcomes.
• Trauma-focused psychological therapy is first-line for PTSD and outperforms medication.
• OCD responds to a specific therapy, exposure and response prevention, that is different from general talking therapy and frequently unavailable.

ADHD

In short: A disorder of the brain's executive control system, present from childhood, and one where treatment measurably reduces real-world harm.

What it is

Attention deficit hyperactivity disorder is a neurodevelopmental condition defined by persistent inattention and/or hyperactivity-impulsivity that is present before age 12, occurs in more than one setting, and causes real impairment.

Three presentations: predominantly inattentive (historically called ADD, and the one most often missed, particularly in girls), predominantly hyperactive-impulsive, and combined.

The name is misleading. It is not a deficit of attention; it is a deficit of attention regulation. People with ADHD can hyperfocus intensely on something engaging and cannot direct attention to something boring but important. The underlying problem is executive function: the set of processes that prioritise, initiate, sustain, inhibit, and switch.

What actually goes wrong

Imaging and pharmacological evidence point to under-functioning of frontal-striatal networks that rely on dopamine and noradrenaline signalling, and delayed maturation of the prefrontal cortex, on the order of a few years.

Executive functions affected:

ADHD is highly heritable, with twin studies giving estimates around 70 to 80 percent. Other contributors include prematurity, low birth weight, prenatal exposures, and early lead exposure. Sugar does not cause it, and neither does screen time, though both are frequently blamed.

Why it matters

Untreated ADHD is not simply an inconvenience. Cohort studies find substantially increased rates of accidental injury, road traffic crashes, substance use disorders, unemployment, relationship breakdown, and premature death. Large registry studies find that periods on medication are associated with lower rates of accidents, injuries, and criminality within the same individuals, which is a stronger design than between-person comparison.

Treatment

Stimulants (methylphenidate, lisdexamfetamine, and related) are the most effective treatment, with response rates around 70 to 80 percent. They increase dopamine and noradrenaline availability in the relevant circuits.

The apparent paradox is not one. People assume a stimulant should make a hyperactive person more hyperactive. In fact, the control network that suppresses irrelevant impulses is under-functioning, so raising its signalling improves inhibition. Stimulants also improve focus in people without ADHD at higher doses, which is why they are misused, and the therapeutic effect in ADHD is on a different part of the curve.

Non-stimulants: atomoxetine (a noradrenaline reuptake inhibitor), guanfacine, and clonidine. Slower to work, useful where stimulants are unsuitable or where tics or anxiety complicate matters.

Non-drug support matters and is not sufficient alone for moderate-to-severe ADHD: behavioural parent training for younger children, environmental structure, external memory systems, and, for adults, coaching and CBT adapted for ADHD.

Side effects of stimulants: reduced appetite, difficulty sleeping if taken late, headache, and small increases in heart rate and blood pressure. Growth velocity may be modestly reduced in children with a small effect on final height. The long-standing concern that treating ADHD with stimulants causes later substance misuse has not been borne out; the evidence points, if anything, the other way.

The diagnostic argument, handled honestly

Adult ADHD diagnoses have risen sharply in many countries, and both concerns are legitimate at once:

• Under-diagnosis is real, particularly in girls and women (whose presentation is more often inattentive and internalising), in adults who developed coping strategies, and in people whose difficulties were attributed to character.
• Over-diagnosis is also plausible where assessment is brief, self-report based, and commercially incentivised, and where symptoms overlap with anxiety, depression, sleep deprivation, and trauma, all of which impair concentration.

The resolution is not to pick a side but to insist on the standard: symptoms present since childhood, in more than one setting, causing genuine impairment, and not better explained by something else. A careful assessment takes hours, not minutes.

Autism

In short: A difference in social communication and sensory processing, present from early development, highly heritable, and not caused by vaccines.

What it is

Autism spectrum disorder is defined by two core features present from early development:

1. Persistent differences in social communication and interaction: reading unstated social rules, reciprocal conversation, non-verbal communication, developing and maintaining relationships.
2. Restricted, repetitive patterns of behaviour, interests, or activities: intense focused interests, insistence on sameness and routine, repetitive movements, and sensory differences, which are frequently the most disabling feature and the least discussed.

The presentation varies enormously, from people needing lifelong daily support to people who are independent and whose difficulties are invisible to others at the cost of constant effort.

Prevalence is estimated at roughly 1 in 100 globally, and higher in countries with more thorough case-finding (around 1 in 36 in recent US surveillance). The rise over decades is attributable largely to broadened diagnostic criteria, better recognition, diagnostic substitution, and increased awareness rather than to a genuine increase of that magnitude.

What actually goes wrong, and framing

Autism is highly heritable, with twin studies giving estimates around 70 to 90 percent, and involves hundreds of genes plus rare variants of large effect. Older paternal age and certain prenatal exposures contribute modestly. There is no single mechanism, and the neurobiology involves differences in connectivity and in how sensory and social information is processed.

Framing matters here more than in most chapters. The neurodiversity perspective holds that autism is a difference in neurological development rather than purely a disorder, and that many difficulties arise from the mismatch between autistic people and environments designed for non-autistic ones. This view is widely held among autistic adults and is compatible with the fact that some autistic people have severe, disabling impairments requiring substantial lifelong support. Both realities are true and any account that only describes one is incomplete.

The goal of support is not to make an autistic person appear non-autistic. Older approaches aimed at suppressing visible autistic behaviours, and there is meaningful evidence that masking, the effortful suppression of natural responses to fit in, is associated with exhaustion, anxiety, depression, and higher suicide risk in autistic adults.

The vaccine claim

Stated plainly because vagueness has not helped. A 1998 paper in The Lancet by Andrew Wakefield proposed a link between MMR vaccination and autism based on 12 children. It was retracted in 2010. The UK General Medical Council found the research dishonest and removed Wakefield from the medical register. Subsequent studies covering millions of children, including a Danish cohort of over 650,000, have found no association. Measles vaccination rates fell in the interim and children died who would not otherwise have died (Chapter 33).

What actually helps

Early support focused on communication, sensory needs, and skill-building; educational adjustments; speech and language therapy; occupational therapy for sensory and daily living needs; and treating the frequently co-occurring conditions, which are the source of much of the distress: ADHD (in perhaps half), anxiety, depression, epilepsy (in around 10 to 20 percent), gastrointestinal problems, and sleep disorders.

Diagnosis in women and girls is systematically delayed, because diagnostic criteria and recognition were built largely on studies of boys, and because girls more often mask and present with anxiety or eating disorders instead. Many are diagnosed only in adulthood, often after their own child is.

Eating disorders

In short: Serious psychiatric illnesses with major physical consequences, and anorexia nervosa has the highest mortality of any psychiatric diagnosis.

Anorexia nervosa is the most lethal psychiatric illness, with mortality estimated at roughly 5 to 10 percent, from cardiac complications, electrolyte disturbance, infection, and suicide. Starvation itself produces bradycardia, low blood pressure, arrhythmias, osteoporosis, infertility, and cognitive changes that worsen the illness, since a starved brain is less capable of the flexible thinking recovery requires.

Refeeding syndrome is a specific and dangerous complication of treating severe malnutrition: reintroducing carbohydrate triggers an insulin surge that drives phosphate, potassium, and magnesium into cells, which can cause cardiac and neurological collapse. It is why refeeding is done slowly, with electrolyte monitoring, in a supervised setting.

Bulimia's physical harms come from the compensatory behaviours: dental erosion from stomach acid, salivary gland swelling, oesophageal tears, and electrolyte disturbance from vomiting and laxatives that can cause fatal arrhythmias.

Treatment.

Early treatment matters substantially. Duration of untreated illness is one of the strongest predictors of outcome, which is the argument for rapid access services and against waiting until someone is thin enough to meet a threshold. Eating disorders occur at every body weight, and a person can be severely ill at a normal or high weight, which is a common reason presentation is dismissed.

Post-traumatic stress disorder

In short: A memory system stuck in emergency mode, with treatments that work well and are frequently unavailable.

What it is. Following exposure to actual or threatened death, serious injury, or sexual violence, four symptom clusters persisting more than a month:

1. Intrusion: flashbacks, nightmares, intrusive memories.
2. Avoidance: of reminders, thoughts, places, people.
3. Negative changes in mood and thinking: guilt, shame, detachment, distorted blame.
4. Hyperarousal: hypervigilance, exaggerated startle, poor sleep, irritability.

What actually goes wrong. The best-supported model is that the traumatic memory is stored without the usual contextual tagging that marks a memory as belonging to the past. It is re-experienced as happening now rather than remembered as having happened. The amygdala is hyper-responsive, the prefrontal cortex under-regulates it, and hippocampal function, which supplies context, is impaired.

Avoidance is what maintains it, because it prevents the new learning that would allow the memory to be updated as no longer dangerous. That is why the effective treatments all involve approaching rather than avoiding.

Treatment. Trauma-focused psychological therapy is first-line and outperforms medication:

Medication (SSRIs, venlafaxine) helps and is second-line. Prazosin specifically reduces nightmares in some patients. Benzodiazepines are actively unhelpful in PTSD and may worsen outcomes by blunting the emotional processing treatment relies on.

Complex PTSD, recognised in ICD-11, adds persistent difficulties with emotional regulation, self-concept, and relationships, and typically follows prolonged or repeated trauma, especially in childhood. It usually requires longer, phased treatment.

Obsessive-compulsive disorder

In short: Not tidiness. Intrusive unwanted thoughts and compulsive rituals, and it has a specific treatment that most people are never offered.

What it is. Obsessions are intrusive, unwanted, distressing thoughts, images, or urges. Compulsions are repetitive behaviours or mental acts performed to reduce the resulting anxiety or to prevent a feared outcome. Affects roughly 1 to 2 percent of people.

Common themes: contamination and washing; doubt and checking; symmetry and ordering; and, less recognised, taboo intrusive thoughts about harm, sex, or blasphemy, which are experienced as horrifying and utterly contrary to the person's values. That last group frequently goes unreported for years because sufferers fear what disclosure would imply about them.

The word "OCD" as casual shorthand for liking things tidy is a genuine problem, because it makes a torturous condition sound like a preference and contributes to people not recognising or disclosing what they have.

What actually goes wrong. Overactivity in a cortico-striato-thalamo-cortical loop, which produces a persistent signal that something is wrong and unfinished. Compulsions relieve that signal briefly, which reinforces them, and the relief becomes shorter with repetition.

Treatment.

Exposure and response prevention (ERP) is the specific first-line psychological treatment: deliberately encountering the trigger and not performing the compulsion, allowing the anxiety to rise and fall on its own. It is uncomfortable, highly effective, and quite different from general supportive therapy. Access to properly trained therapists is the main limitation.

SSRIs at higher doses than for depression, taken for longer before judging response (10 to 12 weeks), are effective. Clomipramine is an option. Augmentation with an antipsychotic is used in resistant cases, and deep brain stimulation exists for severe refractory disease.

Reassurance-seeking is a compulsion. Well-meaning family members who repeatedly reassure are participating in the disorder, and part of treatment is helping them stop, kindly and with the patient's agreement.

Tourette syndrome, briefly

Tics are sudden, repetitive movements or vocalisations, preceded by an uncomfortable premonitory urge that the tic relieves. Tourette syndrome requires multiple motor tics and at least one vocal tic for over a year, beginning in childhood. Coprolalia, involuntary swearing, occurs in a small minority despite dominating popular depictions. Most tics improve substantially by adulthood. Treatment is comprehensive behavioural intervention for tics (CBIT) first, then medication if needed, and treating the frequently co-occurring ADHD and OCD.

What people with these conditions and their families can do

In short: Get a proper assessment, treat what co-occurs, and insist on the specific therapy rather than a generic one.

• Insist on a thorough assessment for ADHD and autism rather than a brief questionnaire, and expect childhood history to be part of it.
• Treat the co-occurring conditions. Most of the distress in autism and ADHD comes from co-occurring anxiety, depression, and sleep problems, all of which are treatable.
• Ask for the specific therapy by name: ERP for OCD, trauma-focused CBT or EMDR for PTSD, family-based treatment for adolescent anorexia, CBT-E for bulimia and binge eating. Generic counselling is not equivalent for any of these.
• Get eating disorders assessed early and at any weight. Duration of untreated illness predicts outcome, and waiting to be "ill enough" is a documented barrier.
• Adjust the environment as well as the person, particularly for autism and ADHD: sensory accommodations, written instructions, external structure, and reduced open-plan noise are not indulgences, they are the reasonable adjustments that make functioning possible.
• Know that stimulant treatment for ADHD is associated with fewer accidents and injuries, so the risk calculation is not treatment versus no risk.

Sources and notes

ADHD prevalence: Polanczyk et al., and Faraone et al., Neuroscience & Biobehavioral Reviews, 2021 (World Federation of ADHD International Consensus Statement). ADHD medication and real-world outcomes: Chang et al., JAMA Psychiatry, 2017 (crash risk), and Swedish and Danish registry within-individual analyses. Autism prevalence: WHO (approximately 1 in 100) and US CDC ADDM Network surveillance. Autism heritability: Tick et al., Journal of Child Psychology and Psychiatry, 2016. Wakefield: The Lancet, 1998, retracted 2010; GMC ruling 2010; Hviid et al., Annals of Internal Medicine, 2019 (657,461 children). Masking and mental health in autistic adults: Cassidy et al., Molecular Autism, 2018. Anorexia mortality: Arcelus et al., Archives of General Psychiatry, 2011, meta-analysis. Family-based treatment for adolescent anorexia: Lock and Le Grange trials. Refeeding syndrome: NICE nutrition support guidance. PTSD treatment hierarchy: NICE and APA guidelines; benzodiazepines in PTSD: Guina et al., Journal of Psychiatric Practice, 2015. OCD prevalence and ERP evidence: Foa et al., and NICE guidance. CBIT for tics: Piacentini et al., JAMA, 2010.

Open questions. The extent of genuine versus diagnostic increase in ADHD and autism prevalence is actively debated. Whether early intensive intervention in autism improves long-term outcomes, and which outcomes should be measured, is contested, with autistic-led research increasingly shaping the question. No medication treats the core features of anorexia nervosa.

Next: the systems this book has said least about, and the conditions within them that affect hundreds of millions of people. 👉