Of greater practical importance, current diagnoses have limited ability to predict prognosis and treatment response. Diagnoses may change over time. Treatments are primarily directed at symptoms or syndromes such as depression or psychosis rather than diagnoses. As a result, patients may go for years until the correct diagnosis is made.

These problems are particularly acute for patients suffering from bipolar disorder, where diagnosis is frequently difficult and for which there are specific medications called mood stabilizers. A study of the Depression and BiPolar Support Alliance (DBSA) membership indicated that bipolar patients on average go seven years and see three to four doctors before the correct diagnosis is made. During this time, they suffer from the uncertainty of their diagnosis. They may also inadvertently be treated inappropriately. Once a diagnosis of bipolar disorder is made, patients still frequently may require trials of several medications over several years before the optimum regimen is determined.

The limitations of psychiatry’s current diagnostic system result in large part from not being based on etiology, or the causes of disease. In other areas of medicine, diagnoses based on collections of symptoms or syndromes have given way over time to diagnoses based on etiology. For example,  jaundice once was a diagnosis. Now it is considered a syndrome that may result from many different possible etiologies from viral hepatitis to tumor or alcohol. Biological tests are used to pinpoint the etiology-based diagnosis.