Dual diagnosis is the occurrence of a psychiatric illness along with a substance abuse problem. An article in Help Guide discusses the ways in which the co-occurring disorders affect each other and interact.  When a mental health problem goes untreated, the substance abuse problem usually gets worse and when alcohol or drug abuse increases, mental health problems usually increase as well. It is estimated that up to 50% of people with mental illness are also affected by substance abuse. Treatment should address both mental illness and substance abuse. To read this article in its entirety, click here.