Six Per Cent: New Research Just Mapped the Mental Health Cliff AuDHD Young Australians Fall Off at 18

A young Australian with co-occurring autism and ADHD turns eighteen. Until that birthday, they had a paediatrician who knew them, a CAMHS clinician who understood the sensory shutdowns, and a stimulant script that worked. Six months later, they have none of those things. They are not in an adult mental health service. They are not in an ADHD clinic. They are not in headspace’s data — they aged out two birthdays ago. They are, statistically speaking, gone.

A scoping review published this year in Child: Care, Health and Development by Tang and colleagues, with research team links to University College London, has just put a number on what AuDHD families have been telling each other in private for years. After screening 1,677 studies across five international databases — Medline, PsycINFO, CINAHL, Scopus and ProQuest Central — the authors found just ten studies worldwide that have looked carefully at what happens to autistic and/or ADHD young people when they try to move from child and adolescent mental health services (CAMHS) to adult mental health services (AMHS). Most of those studies, the review notes, captured the perspectives of clinicians and parents. Only five included the perspectives of the neurodivergent young person themselves.

That alone is a story. The mental health system that fails AuDHD young adults has been so under-studied that a single review can summarise the entire global evidence base in ten papers. And what little we have is grim.

The Australian numbers are even worse than the international average

International evidence is bad enough. A long-running tracking study cited inside the Tang review found that, of all young people who reach the upper age limit of CAMHS, only around 25 per cent are formally transitioned to adult mental health services. Around a third experience an outright disruption or loss of care. Just 4 per cent — yes, four — experience what researchers call an “ideal” transition: planning, joint meetings, continuity of clinician relationship, and no gap in medication or therapy. Young people with neurodevelopmental conditions, including autism and ADHD, are repeatedly identified as the group most likely to fall through the gap, in part because both diagnoses were historically — and wrongly — coded as childhood conditions in adult psychiatry’s mental model.

Australia, on the data we do have, is performing worse than that international baseline.

A New South Wales database study by Nielsen, Nanan, Butler, Nassar and Poulton, published in Australasian Psychiatry in January 2025, tracked stimulant prescribing for children, adolescents and young adults with ADHD across the state. Their finding sits at the centre of this story: of the children who had been treated for ADHD in NSW, only 6.3 per cent had transitioned to an adult psychiatrist by age 25. Even more strikingly, half of those who did start treatment with an adult psychiatrist had no previous treatment record at all — they were not transitioning, they were re-presenting, often after years of medication discontinuation. The treatment prevalence rate fell from 22.8 per 1,000 person-years at age ten down to 2.5 per 1,000 in adulthood, with the steepest drop in the late teens. The childhood male predominance of 4:1 narrowed in adulthood to 1.6:1, partly because women who were missed as girls turn up later — a shadow story of late female diagnosis layered on top of the cliff.

Add the autism dimension and the picture darkens further. AuDHD Australia represents an estimated 650,000 Australians who live with both conditions, with autism-ADHD co-occurrence sitting at 50 to 70 per cent across the published literature. Autistic young people in particular are over-represented among those who fall through the CAMHS gap, because adult psychiatry services rarely take referrals where autism is the primary presenting feature, even though every robust longitudinal cohort to date shows elevated rates of depression, anxiety, suicidality and burnout in autistic adults.

In other words, the eighteenth birthday is a clinical event with a measurable mortality and morbidity tail, and Australia has barely begun to count it.

Why the cliff is steeper for AuDHD specifically

The Tang review identifies the type of barrier, not just the size. Most of the evidence its authors found described institutional barriers: poor communication between CAMHS and AMHS clinicians; lack of clarity about whose role it is to start the transition conversation; ADHD or autism being explicitly excluded from adult community mental health intake criteria in some catchments; medication regimens not being reconciled before handover. What was largely absent from the literature was any systematic look at community and policy barriers — the wider scaffolding of GP supply, Medicare item numbers, NDIS interfaces, and accessible communication that determines whether a young AuDHD person can find an adult service at all.

Two enablers stood out across the included studies. First: involving the young person directly in their own care planning, with adjustments for processing time, sensory environment and predictability. Second: clinicians who tailored their approach — slower pacing, written follow-ups, avoiding open-ended “tell me about yourself” intakes that swallow a freshly unmasked AuDHD nervous system. Both findings echo the 2025 Psychology Board of Australia Code of Conduct, which from 1 December 2025 requires every registrant to demonstrate neurodiversity-affirming and trauma-informed practice, and to make reasonable adjustments. The international evidence and Australia’s new regulatory floor are now pointing in the same direction. The system underneath them has not yet caught up.

What Australia is actually building

This is not a counsel of despair. Several things have already moved.

The National Roadmap to Improve the Health and Mental Health of Autistic People 2025–2035, released earlier this year and supported by $42.2 million in the 2025–2026 federal budget, lists “improving the quality, safety and availability of autism-affirming health and mental health care across the lifespan” as one of its six pillars. The phrase across the lifespan is doing crucial work — it is the first time a national policy document has explicitly named the transition cliff as a problem of policy rather than family logistics.

The National Autism Strategy 2025–2031, of which the Roadmap is the fourth pillar, is now in implementation, with the First Action Plan covering 2025 to 2026 already underway.

State-level ADHD prescribing reforms — the GP-led pathways in NSW from late 2025, Victoria’s $750,000 to train 150 GPs by September 2026, Queensland’s adult GP initiation from December 2025, and Tasmania’s interstate prescription harmonisation that commenced 16 February 2026 — collectively make it more plausible that an eighteen-year-old can keep their script going through a GP rather than disappearing while waiting for an adult psychiatrist appointment that may be twelve months away.

Headspace still serves 12–25-year-olds and is the most accessible national infrastructure that already covers the transition zone. But independent reviews have repeatedly noted that headspace’s clinical depth thins out for young people with complex neurodevelopmental needs, and that its outcomes data has not historically been disaggregated by autism or ADHD status. Orygen, Australia’s Centre of Excellence in Youth Mental Health, led a consortium during the first half of 2025 to advise the federal government on a redesigned youth mental health model of care, and that advice will land in the same policy window as the Tang findings.

Four asks the Tang review makes inevitable

If the international evidence base is ten studies long, Australia has both an obligation and an opportunity to add the next few. Four reforms now read as the minimum credible response.

First, a national CAMHS-to-AMHS transition standard that explicitly names autism, ADHD and AuDHD, requires joint clinics or warm handovers, and is mandated under both the National Roadmap and state mental health plans. The Birmingham experience — joint clinics lifting transition rates from 18 per cent to 55 per cent — is a proof point Australia can copy.

Second, a Medicare item number for integrated AuDHD assessment and review that does not collapse at age eighteen. The current settings push young adults out of paediatric care without a funded landing pad in adult psychiatry or general practice.

Third, headspace and equivalent youth mental health services should be required to publish outcomes disaggregated by neurodivergence, so that the 6.3 per cent figure cannot quietly continue being invisible in national dashboards.

Fourth, and most importantly, the next round of Australian research must treat the AuDHD young adult as the expert witness, not the case study. Of the ten studies in Tang’s review, only five included the neurodivergent young person’s voice. That ratio is itself a finding.

Eighteen is a number, not a clinical event

The most useful reframe for AuDHD families and clinicians right now is also the simplest. The eighteenth birthday is an arbitrary administrative line. The brain on either side of it is the same brain. The depression risk, the medication need, the sensory load, the burnout cycle and the suicidality do not pause for the calendar.

Tang and colleagues have given us a number where there used to be a shrug. Six per cent. Four per cent ideal transitions internationally. Ten studies in the entire world. If you are an AuDHD eighteen-year-old in Australia today, those numbers are not a destiny. They are a map of where the cliff is — and, more usefully, of where the next bridge has to be built.

Sources

Tang Y, et al. Barriers to and Enablers of the Transition From Child to Adult Mental Health Services for Autistic Young People and/or Those With Attention Deficit Hyperactivity Disorder: A Scoping Review. Child: Care, Health and Development, 2026. Wiley Online Library

Nielsen TC, Nanan R, Butler T, Nassar N, Poulton A. Changing patterns of treatment and prescribers of stimulants for children, adolescents and young adults with ADHD in NSW. Australasian Psychiatry, 2025. SAGE Journals

Australian Government Department of Health, Disability and Ageing. National Roadmap to Improve the Health and Mental Health of Autistic People 2025–2035.

Australian Government Department of Health, Disability and Ageing. National Autism Strategy 2025–2031.

ACAMH. Falling through the gap between CAMHS and AMHS.

Orygen, Centre of Excellence in Youth Mental Health. Models of Care Consortium.

If you or someone you know is in distress, contact Lifeline (13 11 14), Beyond Blue (1300 22 4636), or the 13YARN line (13 92 76) for First Nations callers.