The trust said the ADHD service currently received “more referrals in a single month than it was originally commissioned to assess in a whole year”.
The BBC has identified 15 local areas that have closed waiting lists and another 31 that have introduced tighter criteria.
Across the NHS, the average wait time for adults to get assessment is currently eight years and four years for children.
“This situation has become unsustainable, so we’re temporarily stopping new referrals to protect patient safety by focusing on those currently under our care,” Berkshire Healthcare said.
The step was described as “necessary”, but the trust acknowledged it might be “worrying” for patients.
It advised anyone planning to seek a referral to seek guidance from their GP.
Patients who are on ADHD medication will continue to receive care.
There will also be no changes for those transitioning from children’s ADHD services to adult ones.
Patients who have already been referred for assessment, have received a diagnosis and are waiting to start medication will remain on the waiting list.
The trust said it was working with service users, GPs, local authorities, and voluntary organisations to make sure the redesigned service would meet the needs across Berkshire.
It asked that anyone with further queries to contact the healthcare team.