An organic psychosis is an abnormal mental state with a known physical cause characterized by an altered perception of reality. This condition can be acute, as is the case when psychosis is caused by some form of intoxication, or chronic, as is the case with dementia. Organic psychoses can have many different causes, ranging from traumatic brain injuries or drug abuse to the contraction of a brain disease. In each case, however, a physical, biological cause can be found to explain the problem. In contrast, a functional psychosis is an abnormal mental state that can not be traced to a concrete, biological origin.
The symptoms of psychosis may vary greatly from person to person, though all are characterized by an altered perception of reality. Individuals suffering from this condition may experience hallucinations, delusions, and thought disorders of various forms. Hallucinations occur when an individual perceives something, such as a sound or an image, that is not actually present. Auditory hallucinations are the most common of those experienced by those with psychosis, though hallucinations involving all senses can be experienced.
A person suffering from organic psychosis may also suffer from delusions, or beliefs that have no basis in reality. These beliefs often come in the form of paranoia, and a delusional individual may believe without reason that there are people or forces who are actively trying to harm him. Psychotics sometimes suffer from disorders of thought as well, with their ability to form coherent associations often declining as their psychosis worsens. This often becomes apparent through incoherent speech or writing.
There are many different possible causes of organic psychosis. Sometimes, the cause may be as simple and correctable as a fever caused by an infection. The increase in body temperature alters body chemistry and can lead to an acute state of psychosis commonly referred to as delirium. In other cases, it can have a cause that is neither simple nor correctable. Aging, for instance, causes some forms of dementia, such as Alzheimer's disease and Creutzfeldt–Jakob disease. Both have identifiable biological causes and both cause psychosis, but neither can be cured and both tend to worsen over time.
The classification of psychosis has changed over time and the terms "organic psychosis" and "functional psychosis" have fallen out of common use. Psychoses are generally divided into psychosis due to general medical conditions, traditional psychotic illnesses, and substance-induced psychosis. Organic examples can be found within each of these categories.