Dopamine is a substance that is part of the reward system of the brain. It’s a neurotransmitter. These are a kind of ‘messenger substances’ in the brain that transfer information from one nerve cell to another. Dopamine makes us feel satisfied and rewarded. Dopamine is not constantly produced but is released during certain actions or situations such as eating, exercising, sex or drugs. An excess of dopamine can cause important cognitive functions to be disrupted, increasing the susceptibility to psychosis. A low dopamine level makes it difficult to control the muscles, which can lead to muscle stiffness, slow movement and strong tremors, symptoms that occur in Parkinson’s disease. Dopamine also plays a role in schizophrenia and psychosis.