Cause: Dopamine Dysfunction

Many studies have investigated the possible role of brain neurotransmitters in the development of schizophrenia. Most of these studies have focused on the neurotransmitter called dopamine. The "dopamine theory of schizophrenia" states that schizophrenia is caused by an overactive dopamine system in the brain. There is strong evidence that supports the dopamine theory, but there are also some data that do not support it:

Evidence FOR the Dopamine Theory of Schizophrenia:<blockquote>[*] Drugs that block dopamine reduce schizophrenic symptoms. [*] Drugs that block dopamine have side effects similar to Parkinson's disease. Parkinson's disease is caused by a lack of dopamine in a parts of the brain called the basal ganglia. [*] The best drugs to treat schizophrenia resemble dopamine and completely block dopamine receptors. [*] High doses of amphetamines cause schizophrenic-like symptoms in a disorder called "amphetamine psychosis." Amphetamine psychosis is a model for schizophrenia because drugs that block amphetamine psychosis also reduce schizophrenic symptoms. Amphetamines also make the symptoms of schizophrenia worse. [*] Children at risk for schizophrenia may have brain wave patterns similar to adults with schizophrenia. These abnormal brain wave patterns in children can be reduced by drugs that block dopamine receptors.</blockquote>

Evidence AGAINST the Dopamine Theory of Schizophrenia:<blockquote>[*] Amphetamines do more than increase dopamine levels. They also alter other neurotransmitter levels. [*] Drugs that block dopamine receptors act on receptors quickly. However, these drugs sometimes take many days to change the behavior of people with schizophrenia. [*] The effects of dopamine blockers may be indirect. These drugs may influence other systems that have more impact on the schizophrenic symptoms. [*] New drugs for schizophrenia, for example, clozapine, block receptors for both serotonin and dopamine.</blockquote>

Read more here: Schizophrenia