Alcohol and nicotine use have long been known to go hand in hand but other than a commonality in reckless behavior, the reasons why have been speculation.  

Previous surveys have shown that more than 85 percent of U.S. adults who are alcoholics also smoke cigarettes. Now, researchers from the University of Missouri School of Medicine have found that nicotine cancels out the sleep-inducing effects of alcohol, which they believe sheds light on the reason alcohol and nicotine usage are so closely linked.

During the most recent study, rats were fitted with sleep-recording electrodes and given alcohol and nicotine. The researchers found that nicotine acts via the basal forebrain to suppress the sleep-inducing effects of alcohol.

"One of the adverse effects of drinking alcohol is sleepiness,"
said Mahesh Thakkar, Ph.D., associate professor and director of research in the MU School of Medicine's Department of Neurology and lead author of the study.
 "However, when used in conjunction with alcohol, nicotine acts as a stimulant to ward off sleep. If an individual smokes, then he or she is much more likely to consume more alcohol, and vice-versa. They feed off one another.

  "We have found that nicotine weakens the sleep-inducing effects of alcohol by stimulating a response in an area of the brain known as the basal forebrain. By identifying the reactions that take place when people smoke and drink, we may be able to use this knowledge to help curb alcohol and nicotine addiction."