Increased dopamine receptors lead to more dopamine binding and therefore higher levels of dopamine in the brain.
Antipsychotics: Drugs that inhibit dopamine activity lessen the symptoms of schizophrenia - as predicted by the theory.
Iverson (1979): Post-mortems of schizophrenics found excess dopamine in the brain.
PET scans have found that schizophrenics have higher levels of dopamine in the brain and an increased number of dopamine receptors.
L-dopa (a dopamine-releasing drug) can cause schizophrenic-like behaviour in people who have no psychotic disorder.
Antipsychotic drugs only work on positive symptoms so the theory doesn't explain the presence of negative symptoms.
Drugs don't affect all patients in the same way so it's difficult to draw conclusions based on their effects.
Previous drug therapy may have affected post-mortems or PET scans.
The link with dopamine is correlational, so can't infer cause and effect (may be a symptom), however it does suggest an association.
Davis et al (1991): Found that not all schizophrenics have high levels of dopamine, and that clozapine, which doesn't significantly reduce dopamine levels, is an effective treatment in some patients.
Dopamine is involved, but it's not clear how as the theory doesn't give a complete explanation. The…