The gene CYP2A6, which helps produce an enzyme that breaks down nicotine, is more active among most heavy smokers, according to researchers at Japan's Osaka University.

Reuters reported Dec. 6 that researchers examined 300 current and former smokers and found that 70 percent of those with overactive versions of the gene were highly addicted to nicotine. Among less-addicted smokers, only 40 percent had the CYP2A6 gene.

Determining the genotype of smokers could help doctors tailor cessation programs to best suit individual needs, the researchers said.