WASHINGTON - A single pill appears to hold promise in curbing the urges to smoke and drink, according to researchers trying to help people overcome addiction by targeting a pleasure center in the brain.

The drug, varenicline, already is sold to help smokers kick the habit. New but preliminary research suggests it could gain a second use in helping heavy drinkers quit, too.

Much further down the line, the tablets may be considered as a treatment for addictions to everything from gambling to painkillers, researchers said.

Several experts not involved in the study cautioned that there is no such thing as a magic cure-all for addiction and that varenicline and similar drugs may find more immediate use in treating diseases like Alzheimer's and Parkinson's.

Pfizer Inc. developed the drug specifically as a stop-smoking aid.

It has sold it in the United States since August under the brand name Chantix.

Varenicline works by latching onto the same receptors in the brain that nicotine binds to when inhaled in cigarette smoke.

That action leads to the release of dopamine in the brain's pleasure centers. Taking the drug blocks any inhaled nicotine from reinforcing that effect.

A study published Monday suggests not just nicotine but alcohol also acts on the same locations in the brain. That means a drug like varenicline, which makes smoking less rewarding, could do the same for drinking.

Preliminary work, done in rats, suggests that is the case.

"The biggest thrill is that this drug, which has already proved safe for people trying to stop smoking, is now a potential drug to fight alcohol dependence," said Selena Bartlett, a neuroscientist with the Ernest Gallo Clinic and Research Center at the University of California-San Francisco who led the study.

Details appear this week in the journal Proceedings of the National Academy of Sciences.

Pfizer provided the drug for the study, but was not otherwise involved in the research.

In the new study, researchers trained rats to drink alcohol and measured the effect of varenicline once the animals became the laboratory equivalent of heavy drinkers.

They found the drug curbed their drinking.

Even when stopped, the animals resumed drinking but didn't binge.

Just as varenicline doesn't work for all smokers, it's highly unlikely it would for all drinkers, researchers said.