Which disorder is caused by excess dopamine?

• A. Schizophrenia
• B. Parkinson's
• C. Depression
• D. OCD

Answer: (A)

Excess dopamine in specific brain pathways is most closely tied to schizophrenia. When dopamine activity is too high in the mesolimbic pathway, it can produce the positive symptoms you see in schizophrenia—delusions, hallucinations, and disorganized thinking. This link is supported by how antipsychotic medications work: they block dopamine D2 receptors to dampen these symptoms, which helps confirm the role of excess dopamine.

Other conditions fit poorly with the idea of excess dopamine. Parkinson’s disease arises from too little dopamine in the nigrostriatal pathway, leading to motor problems rather than psychosis. Depression involves mood and motivation changes that are more about reduced dopaminergic activity in reward circuits, not an excess. OCD relates to abnormalities in cortico-striato-thalamo-cortical circuits and can involve dopamine, but it isn’t defined by an overall excess of dopamine in the same way schizophrenia is.