|What makes nicotine addictive? Why do some children decide to smoke, while others never light up? What makes quitting smoking so difficult, and how can we make it easier? NIDA-funded researchers are seeking answers to questions like these in nicotine- and tobacco-related studies. Following are highlights of recent gains in our knowledge about nicotine and tobacco.
The NIDA-funded Monitoring the Future survey of students in grades 8, 10, and 12 shows that the number of current teenage smokers has declined since 1997. Still, nearly one in four high school seniors smokes every day, and more than one in eight smokes a half-pack or more each day.
Peer pressure, parental smoking, and family conflicts are the most significant predictors of whether a child makes the transition from occasional smoking to regular cigarette use. In a study of 11- to 13-year-olds, researchers found that 75 percent of the children who smoked had one or two smoking parents. Researchers also found that the earlier teens start to smoke, the more severe their addiction will be. Depression and delinquency also have been shown to be powerful predictors of smoking urges and behavior.
Researchers have found that they can prevent nicotine dependence in mice genetically altered so that they lack a portion of one of the brain receptors at which nicotine binds to produce its rewarding effects. While normal mice self-administered nicotine in laboratory tests, the altered mice did not. Similarly, a natural genetic mutation has been found in humans that inhibits nicotine metabolism. Male smokers with this mutation are less likely to become addicted to nicotine and more likely to find it easier to quit smoking; however, the presence or absence of the defective gene does not affect women's smoking.
In addition to the genetic difference described above, a number of other gender differences have been found among smokers. For example, accumulating evidence shows that, for women, nicotine intake may be less important in smoking behavior than it is for men. Studies have shown that women take fewer and shorter puffs from cigarettes and are less sensitive to some of nicotine's effects, but they may be more sensitive to external stimuli, such as the presence of a lit cigarette or the smell of smoke. Women also have been less successful than men with nicotine replacement therapy for smoking cessation.
In addition to nicotine replacements in the form of gum, skin patches, aerosol spray, and inhalers, medications to aid smoking cessation include the non-nicotine compound bupropion (marketed as Zyban). Bupropion is a prescription antidepressant that also blocks nicotine's pleasurable effects. Other medications used in the treatment of nicotine addiction include clonidine, mecamylamine, and buspirone.
To date, medication combined with behavioral treatment has been the most effective approach to treating nicotine addiction. Behavioral therapies such as relapse prevention/ skills training approaches, motivational enhancement, and group or individual counseling are designed to support both short-term and long-term abstinence from nicotine.
On the Horizon
NIDA has defined new areas of nicotine research to include studies of regional brain metabolism, the role of multiple nicotine receptors, genetic contributions to smoking initiation and persistence, and the phenomenon of craving.
NIDA's Teen Tobacco Addiction Treatment Research Clinic in Baltimore, a new outpatient research program for treatment of nicotine-addicted adolescents, has implemented a 6-month controlled clinical trial addressing the safety, tolerability, and efficacy of two nicotine replacement therapies-gum and patch-in combination with either counseling or group support.
At Washington University in St. Louis, a large-scale gene mapping study is under way to identify candidate genes for risk of nicotine addiction. Researchers are examining adult twins to learn more about the relative contributions of genetic and environmental factors in both smoking initiation and continuing cigarette use.
New medications being studied for treating nicotine addiction include methoxsalen, an approved treatment for psoriasis, and NicVAX, a vaccine that can immunize smokers against nicotine's effects. Methoxsalen reduces the action of an enzyme that metabolizes nicotine and so may help smokers quit more easily. NicVAX has been successful in animal studies and soon will be tested in clinical trials. The vaccine, if successful with current smokers, also might be effective in protecting children from the risk of nicotine addiction.