> But as laboratory scientists know, getting mice or other ani­mals hooked on nicotine all by its lonesome is dauntingly difficult. As a 2007 paper in the journal Neuropharmacology put it, “Tobacco use has one of the highest rates of addiction of any abused drug. Paradoxically, in animal models, nicotine appears to be a weak rein­forcer.”

http://www.salon.com/2013/12/29/sciences_obsession_the_searc...

There's a bunch of on-going research on nicotine gum dependence too. I was a participant in a study for this.