We in the US have bought heavily into the biological side of addictive behavior. I hate to break it to you, but there are NO irrefutable studies that indicate a genetic disposition to addiction. As such, looking at the drug itself is insufficient to indicate its level of addictive potential. Don't forget, some kids get strung out on sniffing Sharpies! The chemical only functions in combination with the behavior. Additionally, associations and expectations play a large role in how addicted we become. Most of us associate smoking with positive social interactions, drinking, a relaxing stroll, a nice break during a hard day's work, etc. And we expect our smoke breaks to be relaxing. I cannot stand the useless direction so much research seems to take in regards to these issues.
On a psychopharmacologic note, nicotine imitates acetylcholine in the brain, and its possible that this peptide functions differently in humans than in animal test subjects.
Cheers,
-Mickey