Dopamine is a member of a class of molecules called the catecholamines, which serve as neurotransmitters and hormones. In the brain, dopamine serves as a neurotransmitter and is released from nerve cells to send signals to other nerves. Outside of the nervous system, it acts as a local chemical messenger in several parts of the body.

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A number of important neurodegenerative diseases are associated with abnormal function of the dopamine system and some of the main medications used to treat those illnesses work by changing the effects of dopamine. The condition Parkinson’s disease is caused by a loss of dopamine secreting cells in a brain area called the substantia nigra.