From Nature:
A new study helps to explain why smokers tend to have boozier nights out than non-smokers. The work, done in rats, shows that a heavy dose of nicotine can cut blood-alcohol levels in half. If cigarettes similarly lower intoxication in people, it could mean that smokers need to drink more than non-smokers to get the same buzz.
Many studies have shown that smokers tend to drink more alcohol than non-smokers, and a number of reasons are proposed for this. People who indulge in one habit may be simply more inclined to indulge in another, and socially both habits tend to go hand-in-hand at pubs and parties. Researchers also know that both nicotine and alcohol trigger a release of the feel-good brain chemical dopamine, but that indulging too much in either habit can breed tolerance to the drugs and reduce this pleasurable reward. So heavy users of one may boost use of the other to help bring their dopamine response back up.
More here.