In-patients as young as 10 were frequently given adult doses of sedatives as a form of control and punishment while at Hill End.
Some were rendered unconscious for hours or days at a time, leaving them vulnerable to abuse by staff.
Adolescents under the age of 16 were referred to the unit between 1969 and 1995 for reasons such as their parents not being able to manage them.
They were made to participate in group meetings and therapy sessions which included controversial massage and touch therapy.
Many of the former patients have received formal letters of apology from Karen Taylor, chief executive of the NHS trust, about what happened to them while they were at the unit.
The letters highlight lessons learned by the trust, which it says have been taken forward into current practice.