If drinking and smoking seem inextricably linked, perhaps it's because in the brain's pleasure centre they actually are.

Alcoholics often have a particularly hard time quitting cigarettes. Traute Flatscher-Bader at the University of Queensland in Brisbane, Australia, and colleagues wondered why this should be. So they did a post-mortem analysis of gene expression in the brains of smokers, alcoholics and those who had done both during their lives.

They found that a group of genes in the nucleus accumbens - an area involved in creating pleasurable feelings - were expressed most strongly in their group of alcoholic smokers (Alcoholism: Clinical and Experimental Research, DOI: 10.1111/j.1530-0277.2010.01207.x).

These genes play a role in rewiring the neurons in the nucleus accumbens. That means people who both smoke and drink might get a greater reward, making it harder for them to quit, says Flatscher-Bader.

Knowing that the link between drinking and smoking may not be purely social could lead to new ways to treat addiction.

http://www.newscientist.com/article/mg20627634.700-trying-to-quit-smoking-the-devil-is-in-the-drink.html