Psychosis refers to an abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality". People with psychosis are described as psychotic. People experiencing psychosis may exhibit some personality changes and thought disorder. Depending on its severity, this may be accompanied by unusual or bizarre behavior, as well as difficulty with social interaction and impairment in carrying out daily life activities.Psychosis (as a sign of a psychiatric disorder) is a diagnosis of exclusion. That is, a new-onset episode of psychosis is not considered a symptom of a psychiatric disorder until other relevant and known causes of psychosis are properly excluded. Medical and biological laboratory tests should exclude central nervous system diseases and injuries, diseases and injuries of other organs, psychoactive substances, toxins, and prescribed medications as causes of symptoms of psychosis before any psychiatric illness can be diagnosed. In medical training, psychosis as a sign of illness is often compared to fever since both can have multiple causes that are not readily apparent.The term "psychosis" is very broad and can mean anything from relatively normal aberrant experiences through to the complex and catatonic expressions of schizophrenia and bipolar type 1 disorder. In properly diagnosed psychiatric disorders (where other causes have been excluded by extensive medical and biological laboratory tests), psychosis is a descriptive term for the hallucinations, delusions, sometimes violence, and impaired insight that may occur. Psychosis is generally given to noticeable deficits in normal behavior (negative signs) and more commonly to diverse types of hallucinations or delusional beliefs, especially as regards the relation between self and others as in grandiosity and pronoia/paranoia.An excess in dopaminergic signalling is hypothesized to be linked to the positive symptoms of psychosis, especially those of schizophrenia. However, this hypothesis has not been definitively supported. The dopaminergic mechanism is thought to be causal in an aberrant perception or evaluation of the salience of environmental stimuli. Many antipsychotic drugs accordingly target the dopamine system; however, meta-analyses of placebo-controlled trials of these drugs show either no significant difference in effects between drug and placebo, or a moderate effect size, suggesting that the pathophysiology of psychosis is much more complex than an overactive dopamine system.