How does the brain get addicted to nicotine?

Nicotine affects the structure of the brain. This change is the root cause of a chemical addiction.

Our model allows the user to try and fill existing receptors on the brain with natural neurotransmitters (chemicals that relay messages between brain cells). But if the user chooses to use nicotine to fill the receptors...more receptors will grow, making it impossible to fill them all without the use of artificially introduced nicotine!