Schizophrenia is a mental disorder that is characterized by at least 2 of the following symptoms, for at least one month:
Only one of the above symptoms is required to make the diagnosis of schizophrenia if the person's delusions are bizarre or if the hallucinations consist of a voice keeping up a running commentary on the person's behavior or thoughts, or two or more voices conversing with each other.
Although the above symptoms must be present for at least one (1) month, there also needs to be continuous signs of the disturbance that persist for at least six (6) months. During this period, the signs of the disorder may be present in a milder form, for instance as just odd beliefs or unusual perceptual experiences. During this 6 month period, at least two of the above criteria must be met, or only the criteria of Negative Symptoms must be present -- if even just in milder form.
For a significant portion of the time since the onset of the disturbance, one or more major areas of functioning such as work, interpersonal relations, or self-care are markedly below the level achieved prior to the onset of the symptoms (or when the onset is in childhood or adolescence, failure to achieve expected level of interpersonal, academic, or occupational achievement).
Schizoaffective Disorder and Mood Disorder With Psychotic Features have been considered as alternative explanations for the symptoms and have been ruled out. The disturbance must also not be due to the direct physiological effects of use or abuse of a substance (e.g., alcohol, drugs, medications) or a general medical condition.
If there is a history of Autistic Disorder or another Pervasive Developmental Disorder, the additional diagnosis of Schizophrenia is made only if prominent delusions or hallucinations are also present for at least a month (or less if successfully treated).
You'll learn more about the different types of schizophrenia in the next section. However, briefly, they are: