At this time there are many theories about what causes psychosis, but no definite answers. Psychosis occurs in a variety of mental and physical disorders; therefore, it likely has multiple causes. Biology, stress and drug use are three of the most common theories.
Neurotransmitters. There is strong evidence that some psychoses involve a dysfunction in neurotransmitters in the brain. Neurotransmitters are the "chemical messengers" of the brain. They transmit impulses throughout the brain and the central nervous system. Of particular importance is the neurotransmitter dopamine. Most antipsychotic drugs that control the positive symptoms of psychosis also block the transmission of dopamine.
Genetics. Individuals whose close relatives experience psychosis are themselves at increased risk. For example, the risk of developing psychosis associated with Schizophrenia in the general population is approximately 1%, yet the children and siblings of those with Schizophrenia have respective lifetime risks of 13% and 9%.
Brain Changes. Changes have been found in the brains of some individuals with Schizophrenia, which appear to have been present since birth or early childhood. Possible causes of the changes include: genetic transmission, abnormal neurodevelopment and pregnancy or birth complications (e.g. exposure of mother to a virus during the second trimester of pregnancy).
Stress. For some people psychosis appears to occur primarily in response to stress. In most cases, it is believed that a vulnerability to psychosis combined with stress will lead to psychosis symptoms.
Drugs. Psychosis can be induced by drugs or can be drug assisted. For example, it appears that amphetamines can cause a psychotic episode, while other drugs, including marijuana, can increase a person's natural vulnerability to psychosis resulting in a psychotic episode.
Vulnerability and Stress
Vulnerability to psychosis is acquired through a genetic predisposition, or as a result of an environmental insult to the brain (brain damage). Vulnerability can be measured by a family history of psychotic disorders, birth complications (e.g. oxygen deprivation of the baby) or brain injuries.
Stresses can be such things as significant life events (e.g. death of a loved one, moving to a new city, etc.), abuse of alcohol and drugs or stressful living conditions (e.g. high levels of family conflict or financial problems).
The degree of vulnerability varies from person to person. Likewise, the amount of stress that may trigger psychosis likely differs for each individual. For example, a person with a low vulnerability might withstand a large amount of stress without experiencing psychosis, whereas, a person with a high vulnerability might only withstand a minimal amount of stress without experiencing psychosis. Is a psychotic person dangerous?
Although some individuals with psychosis may experience mood swings and increased feelings of agitation, they are more likely to present emotional dampening and social withdrawal. While strong delusions and hallucinations may cause a person to react unpredictably or even aggressively, individuals with psychosis are rarely violent and, in fact, they are at much greater risk of causing harm to themselves than to others.