Dopamine is a chemical messenger called a neurotransmitter, which is found in your brain. It carries messages around your brain, telling different parts what to do. Dopamine affects lots of important functions of your brain like behaviour, motivation and reward, sleep, mood, attention and learning. If there isn’t enough dopamine in your brain or it isn’t getting delivered properly you may get conditions that have symptoms to do with these functions like Attention Deficit Hyperactivity Disorder (ADHD), depression or restless legs syndrome.