People can suffer from psychosis without meeting criteria for schizophrenia. Certain medical illnesses and drugs can cause psychotic symptoms. In fact it can be quite difficult to tease apart the relative contributions of mental illness and drug abuse when a substance user has psychotic symptoms. People with mood disorders, such as major depressive disorder or bipolar disorder, can often present with psychotic symptoms. In addition, people under severe stress can sometimes experience psychotic symptoms. The diagnosis of brief psychotic disorder is characterized by quick, transient psychotic symptoms, after which the person returns to normal, generally without need for further medication.