Caffeine - one of the most widely used psychomotor stimulants in the world - it acts on the central nervous system and cardiovascular system by temporarily decreasing tiredness and increasing alertness. According to Dr. Postuma, sleepiness is commonly associated with Parkinson's disease. "We wanted to discover how caffeine could impact sleepiness as well as the motor symptoms of Parkinson's disease, such as slowness of movement, muscle stiffness, shaking and loss of balance."