Addiction to cigarette is mainly due to presence of _______in it.

Tobacco contains a large number of chemical substances including nicotine, an alkaloid.  Nicotine stimulates adrenal gland to release adrenaline and nor-adrenaline into blood circulation, both of which raise blood pressure and increase heart rate. It gives a temporary feeling of energy and pleasure which can dissipate quickly too. This makes a person addictive to smoking.