Adults with attention deficit hyperactivity order (ADHD) do not get enough support from the NHS, a support group has claimed.
ADHD Oxfordshire estimates thousands of people could be living with the condition in the county.
But Patrick Vale, who set up the group, said there was a lack of provision for adults.
The Oxford Health Community Mental Health Team said adults with concerns should see their GP.
In the UK 3% of children have a diagnosis of ADHD, with half of them continuing to have the condition in adult life.
People with the disorder have to deal with problems with concentration, hyperactivity and impulsiveness.
Mr Vale, who was diagnosed with ADHD as an adult, said: "I couldn't find anywhere in Oxfordshire for support.
"You tend to end up going on a downward slide. You'd probably go to your GP with depression or anxiety and if they're not trained to pick up on ADHD it gets missed."
Pritt Buttar, a GP based in Abingdon, Oxfordshire, said: "My patients who are now adults are actually on the same sort of drugs they were on as teenagers, but when you look at the drugs the evidence for them working on adults is just not there."
Professor Eric Taylor, from the Institute of Psychiatry at King's College London, said support across the UK was "patchy" but called it a "developing situation".
He added: "[ADHD in adults] is a relatively new discovery. It's partly an education and training issue because adult psychiatry needs to take it on board.
"There is also a funding issue because adult psychiatry in general is overwhelmed and... can only give a service to the most risky and severe cases."
In a statement the Oxford Health NHS Foundation Trust said adults could be referred to a community mental health team for an assessment to get their appropriate treatment.