WASHINGTON – A single molecule may be partly to blame for nicotine’s addictive allure, a finding that researchers say could lead to potential therapies to help millions of smokers quit a life-threatening habit.

More than 4 million people around the globe – 440,000 of them Americans – die from smoking-related causes each year. And, the nicotine-laced smoke damages more than just their lungs.

In humans, a reward arrives as a pleasant little jolt of dopamine, a calming brain chemical unleashed by nicotine. The body’s tolerance for the drug leads to more smoking. Sensitization means not feeling good without a nicotine fix, said Henry Lester, a biology professor at the California Institute of Technology who was among the paper’s 10 authors.

People become dependent on nicotine when it parks in nerve cell receptors designed for the chemical acetylcholine. Once nicotine fills that space, dopamine is released. By knowing the specific parking place where nicotine goes, a drug could be fashioned to fill it.

“The power lies in the ability to be so specific. In being so specific, you can treat the cause without the ramifications of the side effects,” said Stephen Dewey, a Brookhaven National Laboratory scientist who has studied epilepsy drugs to treat nicotine addiction.

Daniel McGehee, a University of Chicago neurobiologist who has studied a different subset of receptors sensitive to nicotine, called it “a fantastic study” but cautioned against thinking a drug would deliver benefits without costs.

Interfering with how the body experiences the rewards of nicotine could dull other experiences.

“That pathway is not there to promote tobacco use. It’s there to promote healthy behaviors that lead to the survival of our species,” McGehee said. Tampering with it “may interfere with our ability to find pleasure and joy in normal, healthy things.”