Dopamine is a neurotransmitter which is produced by the brains of many organisms, including humans. Like many neurotransmitters, dopamine has several different functions. It plays a critical role in the function of the central nervous system, and it is also linked with the brain's complex system of motivation and reward. Altered levels of dopamine in the brain can cause a range of symptoms and problems, ranging from Parkinson's disease to Attention Deficit Disorder (ADD).

Discovery of dopamine as a distinct neurotransmitter was made in 1952 in Sweden. It is a member of the catecholamine family of neurotransmitters, which includes adrenaline and noradrenaline. All of these neurotransmitters are classified as monoamines, which means that their chemical structure includes an amino group linked with an aromatic ring. The brain biosynthesizes dopamine, taking advantage of precursors produced by or introduced to the body.

In the realm of the central nervous system, dopamine helps the body function smoothly. A decline in dopamine had been classically linked with Parkinson's Disease, a disease which is characterized by problems with the central nervous system. The lack of dopamine makes patients shaky, weak, and confused, and many Parkinson's patients have imperfect control over their bodies.

Dopamine also plays a role in addiction, because it is part of the brain's system of motivation. Some drugs stimulate the production of dopamine, leading to increased dopamine levels and a corresponding high, but when the drug exits the system, it leaves behind a sense of depression and a slowdown, which can only be remedied by increasing dopamine levels again. The brain quickly learns to seek out drugs which will stimulate dopamine production, thereby creating an addiction.

This neurotransmitter is also associated with some psychological conditions, such as psychosis and schizophrenia. It also seems to be involved in attention disorders like ADD, typically in situations where decreased levels of dopamine make it hard for people to focus.

Because dopamine cannot cross the blood-brain barrier, when dopamine is required in neurological treatment, doctors cannot simply give their patients the neurotransmitter directly. Instead, they provide precursors which can cross the barrier, allowing the brain to synthesize dopamine on its own. The neurotransmitter is also sometimes introduced to the bloodstream in treatment for some conditions, since it acts as a diuretic in the body, increasing blood pressure and kidney output.