Why is nicotine considered a drug?

Smokers believe smoking create feelings of, among others, sharpness and relaxation. They believe smoking enhances alertness and consentration, and thus, smokers take deep or quick puffs to either relax or stimulate their nerves.

However, even though most smokers will tell you that smoking is "relaxing", nicotine constricts the blood vessels and raises heart rate and blood pressure.