Stress. The good feeling nicotine gives you. It's a drug that's legal and I'm addicted.
"Immediately after smoking, there is a "kick" caused in part by nicotine stimulation of the adrenal glands and resulting discharge of epinephrine (adrenaline). The rush of adrenaline stimulates the body and causes a sudden release of glucose as well as an increase in blood pressure, respiration, and heart rate, according to the National Institutes of Drug Abuse.
"Additionally, nicotine indirectly causes a release of dopamine in the brain regions that control pleasure and motivation.