"Nicotine is the only known addictive substance that has been proven to alter basic cell chemistry that promotes addiction to nicotine according to research...................."

The article

Researchers find that nicotine changes cell chemistry - Birmingham science news | Examiner.com

The research abstract

Nicotine exploits a COPI-mediated process for chaperone-mediated up-regulation of its receptors


COPI polices nicotine-mediated up-regulation of nicotinic receptors