Parkinson's disease is a condition that affects the brain, resulting in a progressive loss of coordination and movement problems. It is caused by a loss of the cells in the brain that are responsible for producing dopamine, which helps to control and coordinate body movements. People with Parkinson's disease experience a range of motor symptoms, which can fluctuate in severity during the day and between days. Motor symptoms may include dyskinesia (involuntary movement), bradykinesia (slowness) and tremor; non-motor symptoms include sleep disturbances. Starting or adjusting treatment helps to control symptoms. However, these treatments can themselves cause motor-related side effects. An important consideration in decisions about treatment is the need to balance the benefits of treatment with the potential side effects.