A psychological disorder for which no organic cause can be found.
Disorders traditionally classified as neuroses (including a variety of anxiety and mood disorders as well as psychosomatic illnesses) are generally regarded as functional disorders. While conditions classified as psychotic are usually believed to have biological origins, neurotic conditions are generally believed to be caused by developmental, psychosocial, or personality factors. Psychotic disorders not associated with damage to brain tissue from a head injury, infection, or similar causes are also considered functional disorders.
Many mental health professionals are uncomfortable with the term "functional disorder" for a variety of reasons. First, its meaning is often distorted. While the term is essentially a designation of what a disorder is not (i.e., organic), it tends to be interpreted as making positive statements about what the disorder is (i.e., induced by environmental or psychosocial factors) when, in fact, such causes may not have been scientifically proven. In addition, "functional" as a classification continually becomes outdated as new discoveries are made about the origins of certain disorders. Schizophrenia, for example, would be considered an organic disorder if a biochemical cause for the disease—which some researchers believe exists—could be verified. By comparison, the current system of classifying disorders in the Diagnostic and Statistical Manual of Mental Disorders, which is organized by the mental faculty or area of behavior that is impaired, is much less likely to become outdated due to new research. A further objection to the term functional disorder is that it implies an artificial separation of the mind and body, as a number of disorders have both organic and functional components.
Psychology EncyclopediaDiseases, Disorders & Mental Conditions