Harvard conducted an animal study in 2015 to determine addictiveness of nicotine.
To their surprise they couldn’t get any animals to be addicted to nicotine in water.
So researchers requested documents of the tobacco companies, and in the documents they learned that tobacco product manufacturers figured out in the 70's that nobody would repurchase 'light cigarettes', so they had to figure out how to make the tobacco products addictive.
Harvard learned in 2015 what the tobacco giants did to make tobacco products and NICOTINE addictive.
They added a chemical named Pyrazine that is highly addictive, and they have been doing it ever since.
Nicotine is not the addictive substance in tobacco, pyrazine chemical makes tobacco addictive.
Pyrazines are just one of 600 approved chemicals that the FDA allow manufacturers to add to their products in the USA.