Close to 19 percent of American adults, representing 43.8 million people, smoke cigarettes. Smoking is the leading cause of deaths that could be prevented, and accounts for one in five deaths in the U.S, according to statistics from the Centers for Disease Control and Prevention. The reasons people start smoking are varied, but they keep smoking because they become addicted. The general consensus is that nicotine in tobacco is what causes the addiction to smoking, but evidence suggests that it is not the only addictive ingredient. There are over 4,000 compounds in cigarette smoke, and scientists are working to tease those apart and find out what really causes people to become addicted to tobacco. With more information like this, experts can help smokers quit. Tobacco\u2019s Many Components Cigarettes contain more than 600 ingredients, and when burned and smoked, they produce more than 4,000 chemical substances that are inhaled by the smoker and anyone around him. Several of these compounds are poisonous, and at least 50 are known to be carcinogens. Some of the surprising chemicals found in cigarette smoke include acetone, a chemical solvent found in nail polish remover; ammonia; carbon monoxide; cadmium, which is a toxic heavy metal; lead, formaldehyde, a substance used for embalming; and tar, which builds up in the lungs. Nicotine Addiction Nicotine is the main addictive substance found in cigarettes. It is found naturally in the leaves of the tobacco plant. It has several effects on the body when inhaled through cigarette smoke. It causes a rush of adrenaline, which produces a rapid heartbeat, fast breathing and increased blood pressure. Nicotine in the brain also stimulates the release of a neurotransmitter, or brain chemical, called acetylcholine. The flood of this neurotransmitter gives a smoker a quick burst of energy or wakefulness. It also makes the smoker feel better able to pay attention and react to stimuli. Key to what makes nicotine addictive, is that it also releases a flood of the neurotransmitter dopamine. Dopamine is part of the pleasure pathway in the brain, and makes the smoker feel really good for a little while. This pleasurable feeling, enhanced by the release of another neurotransmitter called glutamate, is what keeps smokers coming back for more and what leads quickly to addiction. Soon, the smoker finds himself unable to feel normal without a cigarette. The Other Culprits While no one in the area of smoking research denies that nicotine is the main culprit when it comes to cigarette addiction, scientists believe there is more at work. Studies with rats that were given the choice of tobacco or pure nicotine vapors proved that the animals preferred the mix of chemicals in tobacco. Human studies have shown the same thing. Smokers in one study were offered an IV with pure nicotine or a cigarette, and always chose the latter. Either the experience of smoking, or additional ingredients, contribute to the addictive nature of cigarettes. Researchers are interested in finding out which of the many substances found in cigarettes contribute to addiction along with nicotine. E-cigarettes, which give smokers pure nicotine rather than tobacco smoke, are becoming popular tools for smoking cessation. However, if there are other ingredients that keep people coming back to cigarettes, finding them will help make quitting tools more successful. One possibility is a class of substances called monoamine oxidase (MAO) inhibitors. MAO inhibitors block certain neurotransmitters in the brain and are used as medications to treat depression. They are also found in cigarette smoke. Some researchers believe that smokers may be depressed, and self-medicating with cigarettes. Investigations have already proven that many schizophrenics use cigarettes to self-medicate because nicotine helps produce a protein that is missing in people with this mental illness. Because they contain MAO inhibitors, cigarettes may also give depressives a mood boost and clear up another element of addiction. Research has already proven that depression is a consequence of trying to give up smoking, which may be related to the MAO inhibitors. Another study showed that smokers given lozenges that contain nicotine or those that contain MAO inhibitors got more satisfaction from the latter. Understanding the complex reasons and motivations for smoking, as well as the complex ingredient list in cigarettes, is helping researchers to better understand smoking addiction. When these complicated factors get worked out, experts can devise new and more effective ways to help people turn away from cigarettes. In doing so, they can save lives.