The brain is hard-wired with connections. It is lined with millions of nerve cells called neurons that can send and receive electrical signals. Whenever a cell receives a signal from another cell, an electrochemical impulse passes between them. The second cell passes the signal on by releasing a chemical known as a neurotransmitter that stimulates the nearest neighboring cell to release its own chemical messenger, and so on. This is how the brain communicates with the rest of the body and controls the various functions.
There are many different kinds of neurotransmitters: molecules whose primary function is to deliver packets of information from one neuron to another. One of these is dopamine. Dopamine is similar to adrenaline, affecting brain functions that control movement, pleasure and pain. When we feel happy, it's because dopamine has been released into our system, usually triggered by food, sex, or drugs. In fact, this is what makes dopamine one of the most addictive chemicals.
But the role of dopamine in addiction seems to extend beyond a mere "reward chemical," because it is released when a reward or pleasurable activity is expected, whether it happens or not. So many scientists now believe that dopamine is associated with desire rather than pleasure. For addicts, this means that just thinking about drugs or experiencing visual or other sensory reminders of their drug experiences may trigger release of dopamine and hence intense cravings for the drug.
Dopamine is also called the "pleasure molecule" or the "anti-stress molecule," because it is linked to the "reward site" in the brain