ADHD identification has grown on every axis: US parent-report data show more than 11% of children — around seven million — ever diagnosed, roughly doubling since the late 1990s; adult diagnosis, once considered rare, is the fastest-growing segment, with US adult stimulant prescriptions jumping by double digits during 2020-2022, steepest among young women; and demand has overwhelmed assessment systems worldwide — UK waiting lists for adult ADHD assessment run years in parts of the country, spawning a private-assessment industry with its own quality controversies. Two structural facts frame everything: ADHD is a dimensional trait dichotomised by committee-set thresholds, and diagnosis unlocks controlled substances plus academic and workplace accommodations — making the boundary consequential in both directions and contested by design.

A large share of the boom is correction. The disorder was long conceptualised around hyperactive boys, systematically missing inattentive presentations — disproportionately girls and women who internalised, masked, and collected anxiety and depression diagnoses instead, often reaching ADHD recognition only in adulthood or via their children's assessments. Adults as a category were missed by definition when ADHD was framed as a childhood condition that resolved; longitudinal studies showing persistence into adulthood in a majority of cases dismantled that frame. For well-diagnosed ADHD, the treatment evidence is among psychiatry's strongest: stimulants show large short-term effect sizes, and registry studies associate treatment with reduced accidents, injuries and other real-world harms. Underdiagnosis was never hypothetical; much of the rise is its repair.

The other half is boundary drift with fingerprints. Diagnosis rates track non-biological variables: children young for their school year are diagnosed substantially more than their oldest classmates in country after country — the relative-age effect, immaturity read as pathology; US rates vary widely by state and rose measurably after school-accountability policies made diagnosis administratively valuable; DSM-5 relaxed adult criteria (fewer required symptoms, later onset allowed), expanding the eligible population by design; and the pandemic-era collision of distress, remote life and subscription telehealth produced the industry's stress test — platforms diagnosing in 30-minute video calls with prescriber quotas, ending in federal fraud prosecution (see the telehealth hub). None of this means mild ADHD is fake; it means the boundary region is where diagnosis responds to incentives, and honest practice there requires more care, not less.

The dilution logic from the medicalisation hub applies precisely: treatment effects demonstrated in clearly affected populations shrink toward the boundary, while side effects — appetite, sleep, cardiovascular monitoring, dependence questions — hold constant, and stimulant diversion scales with prescribing volume. The 2022-24 stimulant shortages, driven partly by demand growth, imposed the costs on the clearly affected: patients with unambiguous ADHD rationing medication while prescriptions written on questionnaires flowed. Assessment quality is the lever: thorough evaluation — developmental history, collateral information, differential diagnosis against sleep disorders, anxiety, depression, trauma — protects both the missed patient and the mislabelled one; the questionnaire-plus-prescription model protects neither.

ADHD became social media's flagship diagnosis: billions of views of symptom content that is often relatable to nearly everyone — distractibility, procrastination, forgetfulness are universal experiences that the algorithm packages as diagnostic signs, and content analyses find large fractions of popular ADHD posts misleading. The result is a double distortion: genuinely affected people finally recognising themselves (real, valuable) alongside mass self-identification against criteria no clinician applied — arriving at assessment services convinced, sometimes primed to under-report alternatives. Clinicians now navigate patients as consumers of a diagnosis; the defensible stance treats self-identification as a hypothesis worth evaluating properly — neither dismissed (the catch-up history warns against that) nor rubber-stamped (the telehealth prosecutions warn against that).

For adults wondering: persistent, impairing, lifelong-pattern symptoms across settings justify formal assessment — insist on one that takes history seriously and considers alternatives; be wary of any service whose evaluation fits in half an hour and always ends in a prescription. For parents: relative age matters — a five-year-old youngest in class is often a maturity case, and behavioural and classroom interventions are first-line for mild presentations; for clear cases, treatment works and untreated ADHD has real costs. For everyone: diagnosis is a tool, not an identity or a verdict — the goal is function, reached sometimes with medication, always with structure, and never through a questionnaire funnel. And a diagnosis boom is not a hoax epidemic: it is medicine renegotiating a boundary in public, with genuine patients on both sides of every line drawn.