ADHD – attention deficit hyperactivity disorder – affects the way the brain works and can cause people to act impulsively and become easily distracted.
It is thought to affect 5% of children and 3-4% of adults, although many remain undiagnosed.
Getting a diagnosis and treatment, which can include medication and psychological therapy, can be life-changing, experts say.
But NHS data already shows average waits of eight years once someone is on a waiting list.
And now a BBC investigation has found a significant number of areas are restricting access to those waiting lists.
The BBC received information from 59 services, which accounts for the majority of those providing support in England, after submitting freedom of information requests.
The responses showed:
15 trusts had halted all or part of their referrals – some cover large areas and have closed their waiting lists to just some places
In Cheshire, the service for adults has been closed to new patients since 2019
Of the remaining trusts, 31 were rationing care by bringing in exclusions, such as by age or severity
One trust, Coventry and Warwickshire Partnership Trust, is being threatened with legal action for restricting adult assessments to people under 25 only
In some areas, people referred for support by GPs can use something called ‘right to choose’ to go onto another NHS list or ask for private support, which would provide an alternative option if their local NHS has stopped taking on new referrals.
The BBC investigation also found examples of areas that are innovating. One of those is Surrey where the local service, which has 11,000 adults on its waiting list, is piloting a scheme to train a group of private GPs to carry out assessments and treatment.