Defining mental illness: An interview with a Mayo Clinic specialist

A Mayo Clinic psychiatrist offers answers to frequently asked questions about mental illness, including causes, classifications, treatments, the effects of stress and more.

Mental illnesses have been recognized for thousands of years. Today, advances in science are helping researchers better understand the origins of mental illness and find more effective treatments. But much remains to be learned. Here, Daniel Hall-Flavin, M.D., a psychiatrist at Mayo Clinic, Rochester, Minn., offers a modern interpretation of mental illness, including a look at how mental disorders are defined, the use of medications, the role of psychotherapy and how stress affects well-being.
What is mental illness?
Mental illness is a term that refers to all the different types of mental disorders, including disorders of thought, mood or behavior. To be classified as a mental illness, the condition must cause distress and result in a reduced ability to function psychologically, socially, occupationally or interpersonally.
This means that someone who has a mental illness may have trouble coping with emotions, stress and anger, for instance, and trouble handling such things as daily activities, family responsibilities, relationships, or work and school responsibilities. You can have trouble, to a greater or lesser degree, with one area or all of them. And you can have more than one type of mental illness at the same time.
How is the classification of mental illness evolving?
Today, we classify mental illness based on the symptoms a person experiences and the clinical features of the illness, such as feeling hopeless or having delusions. But as we continue to gain a clearer understanding of how specific genes interact with illnesses or behaviors, we may be able to develop a much more sophisticated classification system that is directly linked to a biological cause of mental illness, rather than just symptoms. This can help us better tailor treatment to individuals. For instance, some disorders have similar symptoms and clinical features but are actually very different in terms of their underlying biology. To treat them similarly simply because they share the same symptoms may not be appropriate. We suspect, for example, that there are different types of schizophrenia, with different causes, and that they possibly respond differently to different treatments.
What are the classes of mental illness?
Our evolving understanding of genetics and how the brain works may eventually change how we classify mental illnesses. For now, we think of several main classes of mental illness:
Mood disorders. These include disorders that affect how you feel, such as persistent sadness or feelings of euphoria. They include major depression and bipolar disorder.
Anxiety disorders. Anxiety is an emotion characterized by the anticipation of future danger or misfortune accompanied by a feeling of being ill at ease. Examples include panic disorder, obsessive-compulsive disorder, specific phobias and generalized anxiety disorder.