Some people crave the buzz of a cigarette; others cringe at the idea of lighting up. The difference? Nonsmokers may have a gene which keeps them from chasing that high.

Two studies provide the first evidence that having a gene called SLC6A3-9 reduces a person’s risk of starting smoking. It pushes back the age at which smokers begin and makes it easier to quit for longer periods.

Nicotine stimulates the release of the neurotransmitter dopamine, triggering the brain’s “pleasure pathway.” But SLC6A3-9 reduces dopamine transmission so that smoking doesn’t impart as much of a buzz.

Psychologist Caryn Lerman, Ph.D., of Georgetown University compared the DNA of nonsmokers and chronic smokers. Non smokers were most likely to have the SLC6A3-9 gene, and smokers with the gene were less likely to have started lighting up before age 16. They had also quit in the past for much longer periods. Dean Hamer, Ph.D., then examined smokers, former smokers and nonsmokers and found that subjects with the gene also scored over one point lower in novelty-seeking than those without it. Thus, the gene kills the thrill people normally get from nicotine. Smokers, however, are more impulsive. “They do things without thinking them through,” says Hamer, a researcher at the National Cancer Institute. “Smoking could lead to cancer.” Genetic testing may one day weed out novelty-seekers-so doctors can help daredevils get highs from a less hazardous source.