Why smoking leads to alcohol addiction

Smoking can make people crave alcohol to the point where they become addicted to it.

Senior author and biologist at The Scripps Research Institute (TSRI), Oliver George, said conducted a study using rat model sand said that it was a "vicious cycle" where nicotine made people crave alcohol to reward the brain and reduce stress.

The team first tested whether nicotine exposure could affect alcohol-drinking behavior in rat models. They started with two groups of male rats where both groups were given access to alcohol to establish the baseline of how much they would drink. The rats drank a little bit, perhaps the equivalent of one or two beers for a human, but they stopped before showing signs of drunkenness.

After this, the researchers used alcohol vapor to induce alcohol dependence in one group of rats. Dependence developed in about two months. In subsequent tests where alcohol was freely available, these rats consumed the equivalent of a six-pack of beer and had blood alcohol levels close to three times the legal limit for humans.

The second group of rats were exposed to both nicotine and alcohol vapor. These rats developed alcohol dependence much faster-and they began drinking the equivalent of a six-pack in just three weeks.

The researchers then offered the rats alcohol with the bitter compound quinine added to see if they could stop the rats from drinking. Most rats decreased their alcohol consumption to avoid the bitter taste, but the nicotine-exposed rats just kept drinking. This indicated that their behavior was compulsive, much like alcoholism in humans.

Using further neurological studies, George and his colleagues tracked this compulsive behavior to the activation of "stress" and "reward" pathways in the brain.

The compulsive alcohol consumption and neurological pathways seen in the new study suggest that alcohol works with nicotine to further activate the brain's reward system and dampen the stress of nicotine exposure.

The study is published in The Journal of Neuroscience.