In Chapter 2, we define mental illness and introduce readers to the DSM-5 as a diagnostic system. We outline diagnostic criteria for schizophrenia, bipolar disorder, major depressive disorder, and borderline personality disorder to present readers with the diagnoses of the 118 participants in our life story analyses. We discuss limitations of viewing mental illnesses as delimited categories, including studies showing high comorbidity, and review evidence that transdiagnostic approaches hold advantages. We conclude the chapter by providing rationales for approaching the two questions in our life story analyses from a transdiagnostic perspective.

Valid diagnostic standards are important for both the treatment and scientific study of SUD. Primary features of SUD are uncontrolled compulsive drug use, and harmful consequences of drug use. The DSM-5, a successor to the DSM-IV, lists diagnostic criteria for SUD, and its use is the standard for diagnosis of the disorder. Physiological withdrawal symptoms are only 1 of 11 possible criteria, so are neither necessary nor sufficient for a positive diagnosis. Differences among individuals in gender, psychiatric disorders, and other factors can influence the diagnosis of SUD. Less severe cases may be difficult to distinguish from heavy but non-pathological use of drugs, including alcohol. Screening tests cannot provide a diagnosis, but can identify individuals whose drug use warrants a full diagnostic interview. For those with an SUD, the diagnostic interview can be the initial phase of treatment by establishing a therapeutic relationship with a mental health professional. A skilled clinician can often counteract the denial and defensiveness that can prevent an accurate diagnosis of SUD.