SACRAMENTO, Calif. — Given that 85 percent of alcoholics also smoke, a drug recently approved as a stop-smoking aid may turn out to be a pharmaceutical two-for-one deal.

Varenicline, marketed by Pfizer as Chantix to help people stop smoking, helped rats kick their drinking habit, according to a study published this week in the Proceedings of the National Academy of Sciences. This paves the way for clinical studies using this drug to treat alcoholism.

"Varenicline is the first drug on the market for nicotine cessation that's not nicotine itself. It's safe," said Selena Bartlett, senior author on the study. "We were surprised to find that this drug also serves to reduce alcohol drinking in animals."

Bartlett directs preclinical development at the Ernest Gallo Research Center at the University of California-San Francisco.

For the study, researchers trained rats to drink in order to test the drug's affect on alcohol consumption. Although visions of rats stumbling around in a drunken stupor are off the mark, Bartlett's lab got rats to be "social," "chronic," or "heavy" drinkers.

When the drug was given at the dose that stems nicotine craving in animals, the amount of alcohol consumed decreased by about half. If given over six days, alcohol intake was reduced over the whole period.

Since "withdrawal" from a drug could lead to an even greater desire for alcohol, Bartlett's team monitored drinking after the last dose of varenicline was given. Coming off the drug did not result in a bad rebound — alcohol intake was not more than it was before taking the drug.

Why would a stop-smoking drug curb alcohol craving?

Nicotine and alcohol both trigger the brain's reward system. While food, sex and exercise tickle the system, drugs hijack the system and send it into overdrive.

The reward comes when nicotine binds to a protein that triggers a "feel-good" chemical called dopamine. A craving comes when the amount of dopamine drops. Varenicline works by binding to the same protein and blocking nicotine. It results in a lower, but constant level of dopamine reducing the craving that lead to relapse.

Since alcohol indirectly activates the same protein as nicotine, varenicline likely curbs alcohol craving in the same way as it helps with nicotine.

Approval of the drug in humans for alcoholism may be faster than for a drug that has never been tested in humans.

In addition to medication, behavioral treatments such as Alcoholic Anonymous are available.