Why do many adults only realise they are neurodivergent later in life?

ADHD and autism are among the most commonly missed diagnoses in adults in the UK. Despite growing awareness, the majority of people who live with these conditions reach adulthood without ever receiving a formal assessment. This article explores the systemic, structural, and diagnostic reasons why that happens, and why the barriers are especially pronounced for women, girls, and people who present in ways that fall outside the narrow historical template.

Systemic and structural barriers within healthcare

Gaps in clinician knowledge and specialist training

The starting point for most people seeking a diagnosis is their GP, yet standard medical training provides limited education on neurodevelopmental conditions. This gap has significant consequences for how early, and whether, someone gets referred.

ADHD and autism are rarely given substantial space in general medical or psychological training curricula, meaning that many clinicians working in primary care have limited grounding in how these conditions present across different ages and life stages. Diagnostic criteria have also evolved considerably over recent decades, but continuing professional development on neurodevelopmental conditions remains inconsistent across the profession. When a clinician is more familiar with anxiety or depression than with ADHD or autism, there is a natural tendency to default to those more recognisable diagnoses. This is not a matter of bad faith; it is a structural knowledge gap with real consequences for patients.

Referral patterns and assessment bottlenecks

Even where a GP suspects a neurodevelopmental condition, the route to assessment is far from straightforward. Referral practices vary significantly between regions, and the pathways that do exist are often poorly joined up.

GPs frequently under-refer patients who raise concerns about ADHD or autism, sometimes dismissing symptoms as falling below a perceived diagnostic threshold or attributing them to stress and circumstance. Where referrals are made, they may route through general mental health services rather than directly to specialist neurodevelopmental teams, adding further delays and sometimes diverting individuals entirely. The result, for many people, is being passed between services without ever receiving a formal evaluation. In England, whether someone can access a timely assessment often comes down to postcode, a reality that creates a significant equity problem within what should be a universal system. The NHS Right to Choose policy, introduced in 2018, allows patients to request referral to any eligible provider offering NHS-funded assessments and has provided a faster route for some, but the picture is increasingly unstable: some integrated care boards have instructed providers to pause bookings for patients in their area entirely, meaning that even this route cannot be relied upon consistently.

Funding constraints, shortages, and waiting times

Perhaps the most visible barrier in the UK context is the scale of waiting times for NHS neurodevelopmental assessments. Chronic underfunding has produced capacity shortages that leave many adults waiting years for an appointment.

As of December 2025, there were over 562,000 open referrals for a possible ADHD assessment in England, with around six in ten adults having been on a waiting list for over a year. There is no national target for ADHD assessment waiting times, which means local commissioning bodies bear the burden of managing demand without the political accountability that targets would create. Autism assessment waiting times tell a similar story: NHS England data from December 2025 shows that 90% of patients with an open autism referral had been waiting more than 13 weeks beyond the recommended threshold. For people who can afford it, private assessment offers a faster route, but at a cost that places it out of reach for a significant proportion of adults. The financial barrier is not incidental; it means that access to diagnosis is, in practice, partly determined by income.

Inadequate screening tools and assessment quality

The tools used to screen and assess for ADHD and autism were not designed with the full range of presentations in mind. This limitation means that many people, particularly those with more subtle or atypical profiles, are missed.

Many screening questionnaires were developed and validated primarily on male, child populations, and their continued use with adults, women, and people from diverse backgrounds produces systematic blind spots. Brief screening tools may flag classic presentations while missing the nuanced, compensated profiles common in adults who have spent years developing workarounds. When no standardised, evidence-based assessment framework is applied consistently across services, the quality of what an individual receives varies enormously depending on where they live and who they happen to see. Co-occurring mental health conditions can further complicate matters by obscuring neurodevelopmental traits during evaluation, a pattern sometimes described as diagnostic overshadowing, where the presenting mental health condition becomes the focus and the underlying neurodevelopmental profile goes unexplored.

Diagnostic complexity, bias, and misrepresentation

Masking, camouflaging, and hidden presentations

One of the most significant reasons ADHD and autism go unrecognised is that many people become highly skilled at hiding their difficulties. Masking and camouflaging are active, effortful strategies that can render someone essentially invisible to a clinician in a brief appointment.

Masking refers to the process of suppressing or concealing autistic or ADHD traits in order to appear neurotypical. This can involve rehearsing conversations in advance, suppressing physical responses such as stimming, mirroring others' social behaviour, and sustaining a performance of competence that is exhausting to maintain. Over time, masking becomes so habitual that many people are barely aware they are doing it. The problem, from a diagnostic perspective, is that a person who has spent twenty or thirty years developing these strategies may present to an assessor as someone who does not meet diagnostic thresholds, even when their daily lived experience is profoundly affected. Clinicians who interpret the absence of overt symptoms as evidence against a diagnosis will miss this population entirely.

Gender differences and the diagnostic gender gap

The gender gap in ADHD and autism diagnosis is one of the most well-documented and consequential failures in this area of medicine. Women and girls are diagnosed later, less frequently, and often only after accumulating years of secondary mental health difficulties.

ADHD and autism research and diagnostic frameworks were built almost exclusively around the presentation of young males. Girls with ADHD more commonly present with inattentive rather than hyperactive-impulsive symptoms: they are more likely to be quietly struggling than visibly disruptive, and quiet struggle is less likely to prompt a referral. Autistic girls and women often develop stronger social motivation and more sophisticated social mimicry than their male counterparts, making their difficulties harder to detect by clinicians applying a male-centric template. Gender stereotypes compound the problem, with symptoms in females frequently attributed to anxiety, emotional sensitivity, or personality rather than to a neurodevelopmental profile. The result is that many women spend decades receiving treatments that address the symptoms of masking rather than the underlying condition. Research is increasingly identifying similar diagnostic disparities affecting non-binary and transgender individuals, who are both more likely to be autistic and more likely to face barriers to recognition and assessment.

Stereotypes, misconceptions, and misinformation

Public and clinical misconceptions about what ADHD and autism look like continue to shape who gets referred and who gets missed. These stereotypes are narrow, outdated, and actively harmful.

The dominant cultural image of an autistic person often centres on severe social withdrawal or significant intellectual disability. The dominant image of someone with ADHD is frequently a hyperactive young boy. Neither picture reflects the actual diversity of presentations in the adult population. These archetypes are reinforced by media portrayals that draw on a narrow slice of lived experience, and they shape clinical expectations in ways that are difficult to counteract. A clinician who holds an implicit picture of what ADHD or autism should look like may unconsciously discount the presentation of a professional woman in her forties who is articulate, high-functioning in some areas, and quietly falling apart in others. Misinformation is not solely a public problem; it operates within clinical settings too.

Misdiagnosis, premature closure, and diagnostic substitution

For many people, the path to a correct neurodevelopmental diagnosis runs through a series of incorrect ones. Misdiagnosis does not just delay the right support; it can cause active harm through years of ineffective treatment.

Conditions such as anxiety, depression, OCD, and borderline personality disorder share surface-level features with ADHD and autism, and they are frequently diagnosed first. Once a mental health diagnosis is in place, a form of premature clinical closure can occur: subsequent clinicians attribute all presenting symptoms to the existing diagnosis, and the possibility of an underlying neurodevelopmental condition goes unexplored. This is distinct from the diagnostic overshadowing described above, though the two can compound one another. 

The relationship between ADHD and bipolar disorder is particularly complex and warrants careful handling. The two conditions co-occur at significant rates, estimated at between 10% and 20%, and their overlapping features, including mood dysregulation, impulsivity, and sleep disturbance, mean that each can cause the other to be missed rather than one simply being substituted for the other. The more important clinical problem is not straightforward misdiagnosis but missed comorbidity. Autism in women is more clearly documented as being misdiagnosed as emotionally unstable personality disorder, a pattern supported by multiple peer-reviewed studies and attributable to the symptom overlap between the two conditions, combined with gender bias in how emotional dysregulation and social difficulties are interpreted clinically. Both errors lead to treatment that addresses the wrong target. For individuals on the receiving end, repeated misdiagnosis also erodes trust in healthcare, making it harder to seek help again.

Stigma, dismissal, and invalidation

Stigma operates at multiple levels in the diagnostic process. It shapes whether someone seeks assessment in the first place, how they are received when they do, and whether they feel safe continuing to engage with services if dismissed.

Social stigma around neurodevelopmental diagnoses leads some people to avoid seeking assessment for fear of how a label might affect their career, their parenting, or how others see them. When people do come forward, they often report being dismissed by clinicians who suggest their concerns are driven by social media rather than genuine experience. This kind of response does not just delay diagnosis; it actively discourages people from returning. 

Internalised stigma, particularly in adults who have spent years developing coping strategies, can also cause individuals to minimise or rationalise their own difficulties, telling themselves that what they experience is simply how life feels for everyone. Being told that problems are due to stress or personality, when a neurodevelopmental profile is actually present, is a pattern that appears repeatedly in the accounts of people who eventually receive a late diagnosis, and it is one that clinicians and commissioners need to take seriously.

Adult diagnosis challenges and lifespan underdiagnosis

The assumption that ADHD and autism are primarily childhood conditions has created a structural bias against adult diagnosis that persists in both services and clinical attitudes.

Adult assessment services are significantly fewer in number than paediatric services, which reflects a historical framing of these conditions as something children grow out of rather than something adults live with. Many adults seeking diagnosis were simply missed in childhood: their presentations were milder, their intelligence allowed them to compensate, or awareness was insufficient at the time. 

Adult assessments also require retrospective evidence of childhood traits, which places significant demands on both the individual and their records, and introduces the additional challenge of recall bias. Adults who do reach assessment often encounter an additional layer of scepticism from clinicians who question why difficulties were not identified earlier. This question, however well-intentioned, misses the point. The answer is usually that the barriers described throughout this article applied just as thoroughly when they were children.

Summary

ADHD and autism go undiagnosed in adults for reasons that are structural, clinical, and deeply human. Chronically underfunded services, undertrained gatekeepers, inadequate screening tools, and postcode variation in referral practice form the systemic backdrop. Layered onto this are the diagnostic complexities of masking, gender bias, stereotyping, misdiagnosis, and stigma, each of which can derail the path to an accurate assessment. The cumulative effect is that many adults, particularly women and those who present in ways that fall outside the traditional diagnostic profile, spend years or decades without answers. Understanding these barriers is not just academically interesting; it is practically important for anyone who suspects they may be neurodivergent and is trying to navigate a system that was not designed with them in mind.