Smoking and drinking are two vices that often go hand in hand (one hand clutching a drink while the other holds a smoke). A decade ago, a study in the Journal of Studies on Alcohol indicated that as many as 85 percent of heavy drinkers also light up. Smokers have various aids to help them quit the deadly habit, including varenicline, a drug manufactured by Pfizer that blocks nicotine from releasing the pleasure-associated neurotransmitter dopamine. Now new studies in rats show that it also blocks a craving for alcohol.

Eighteen rats were given intermittent access to 40 proof alcohol for four months. By varying access to the liquor this way, pharmacologist and alcohol researcher Selena Bartlett of the Ernest Gallo Clinic & Research Center at the University of California, San Francisco, and her colleagues made rats crave it. Every time the rodents had access to booze, they upped their intake. "They drink all day and then they don't get to drink," Bartlett says. "The withdrawal makes them want to drink more."

But even after months of this behavior—37 binge-drinking sessions in all—the rats cut their drinking in half when given varenicline. And when taken off the drug, the rats did not immediately imbibe more (the so-called rebound effect that has plagued other treatments). "That's because we believe [the drug] is turning down the reward system," Bartlett says, "instead of replacing the system."

Bartlett believes that varenicline works by fastening onto receptors in the brain that would otherwise be activated by alcohol (or nicotine). A synthetic drug—modeled after the alkaloid cytisine from the small flowering Laburnum trees of Europe chemically combined with a compound from the poppy plant—it also curbed drinking in seven rats with continuous access to alcohol and 30 rats trained to self-administer liquor when stressed.

Varenicline has been available as a smoking cessation aid for nearly a year in the U.S. and the European Union, 30 countries in all. In addition to already having proved its safety in humans, the drug offers other benefits over current alcoholism treatments, including not diminishing appetite. Also, "it's not metabolized in the liver," Bartlett says, a major plus because "people who have been drinking for a long time tend to have liver damage."

The researchers plan to conduct clinical trials on humans pending permission and funding by the U.S. National Institute on Alcohol Abuse and Alcoholism in Bethesda, Md. It remains unclear how long a treatment would need to be in order to kick the habit but the drug does linger longer in the human system. "In rats, the drug only lasts for a few hours," Bartlett says, although it still cuts drinking in half. "In humans, it lasts 24 hours." And some alcoholics who are trying to quit smoking may already be feeling the benefits.