A Dual Diagnosis is when a person has both a Mental Health condition and a substance use disorder. TreatmentDual Diagnosis is when a person has a mental health condition and substance use disorder. Psychotherapy is often a key part of treatment for dual diagnosis, especially cognitive behavioral therapy (CBT). A person who has a substance use disorder and a mental health problem may require an integrated approach to treatment. Other factors such as high levels of stress and trauma may also contribute to the development of a dual diagnosis.