Dual diagnosis is a term used to describe people with serious mental health problems who also have drug or alcohol dependency.Both these broad conditions are classed as illness in the International Classification of Diseases by the World Health Organisation.Thus,dual diagnosis is taken to mean two illnesses, with their separate diagnoses, existing alongside each other. In some ways this is helpfull, as it signals a need for services that can address both conditions simultaneously. It marks and advance of a sort for,until recently, drug services would not provide for people with serious mental health problems, and mental health services would not treat substance misuse. Today there are 3 different approaches to dual diagnosis:

1.drug and mental health services treat the person simultaneously but separately

2.consecutive treatment, one after the other

3.integrated service, addressing both conditions and how they interact with each other.