Nicotine in tobacco is the primary reason why most people find it hard to stop using tobacco. Clinical trials have provided evidence that there are several drugs that can help people quit smoking. These drugs work by either mimicking the positive impact that nicotine has on the brain of a smoker or lessening symptoms of nicotine withdrawal that typically occur a when a smoker stops using tobacco.
As summarized in the 1988 Surgeon General's Report on Smoking and Health - and more recently in tobacco industry documents- there is no doubt that nicotine in tobacco is the primary reason why most tobacco users continue to expose themselves to the known toxins found in tobacco.
Nicotine creates dependence by stimulating the release of chemicals that make a person feel better. Over time, higher levels of nicotine are required to unleash the chemicals and reproduce the positive feeling, which explains why most smokers start out smoking infrequently and eventually increase their smoking to about a pack per day. When smokers stop smoking without any assistance, the abrupt discontinuation of nicotine can cause bad moods and other symptoms of nicotine withdrawal, which make it likely that the effort to quit will fail.
This problem has led to the development of smoking cessation treatment methods that emphasize nicotine replacement or nicotine mimicry. Nicotine mimicry, which is the goal of the newly engineered compound Varenicline, decreases nicotine withdrawal by weakly stimulating the body's nicotine receptors, while also decreasing the "high" of nicotine itself by binding much more strongly to the receptors, blocking nicotine uptake.
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Silagy C, Lancaster T, Stead L, Mant D, Fowler G. Nicotine replacement therapy for smoking cessation. Cochrane Database Syst. Rev. 2002; 4:CD000146.
U.S. Department of Health Hum. Serv. The Health Consequences of Smoking: Nicotine Addiction. A Report of the Surgeon General. Rockville, MD: U.S. Department. Health Human. Services, Centers for Disease Control, Office on Smoking or Health, 1988.