Tobacco usage is known to be one of the leading causes of death, with 7 million worldwide dying each year as a result of smoking cigarettes, or chewing tobacco products. There are also many around the world that do not smoke, but inhale cigarette smoke as a result of being exposed to smokers, in a phenomenon known as secondhand smoke . Nicotine, the primary chemical found in cigarettes and other tobacco products, has dangerous effects on multiple parts of the bodies of smokers and those who inhale secondhand smoke, including the lungs. Although its impacts on neural function are not as well known, nicotine is known to cause addiction and cognitive decline. These effects make it increasingly hard for smokers to both quit smoking and live comfortable lives.
How Nicotine Enters the Brain:
Following inhalation of a cigarette, or the chewing of a tobacco product, nicotine (C10H14N2) enters the brain by traveling through the bloodstream. Nicotine is then able to bind to receptors in the brain, known as nicotinic acetylcholine receptors throughout the brain, where they imitate the behavior of the neurotransmitter acetylcholine. After binding to the receptors, nicotine can activate ion channels throughout the brain, altering memory and muscle contraction, which are functions of acetylcholine.
Fig. 1: Shown here is the brain’s dopamine reward pathway, triggered when nicotine enters the brain
Nicotine from cigarettes and other tobacco products trigger the reward pathway in the brain, which allows people to feel energized while smoking. In the reward pathway, nicotine molecules move to an area of the brain known as the ventral tegmental area, where the chemical dopamine is synthesized. The ventral tegmental cells are associated with the nucleus accumbens area, where dopamine is released, and the prefrontal cortex which is in charge of making decisions. Dopamine is the primary chemical involved in reinforcement, so this causes smokers to repeatedly smoke (for the pleasure associated with dopamine release), eventually to become addicted to smoking.
The more that people smoke tobacco products, the greater the risk for neurodegenerative diseases, such as Alzheimer’s disease and dementia. Several studies have demonstrated that smokers are about 80% more likely to be diagnosed with all types of dementia, including Alzheimer’s disease. Although the causes are not well known, some studies have attributed the oxidative stress increase from smoking to the development of Alzheimer’s disease.  However, if one stops smoking cigarettes or chewing tobacco products, the risk for all types of dementia is shown to have reduced significantly. 
With the advent of World No Tobacco Day, on May 31, it is important to remember that tobacco is a drug that harms bodily function to a great extent. Even trying to smoke or chew tobacco products could lure people into addiction and cognitive decline. All the adverse effects of tobacco and nicotine should urge people to improve their health by not smoking or quitting smoking.
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- NIDA Blog Team. “Why Is Nicotine So Addictive?” National Institute on Drug Abuse. Last modified February 4, 2019. Accessed May 22, 2020. https://teens.drugabuse.gov/blog/post/why-nicotine-so-addictive.
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- Durazzo, Timothy C., Niklas Mattson, Michael W. Weiner, and Alzheimer’s Disease Neuroimaging Initiative. “Smoking and Increased Alzheimer’s Disease Risk: A Review of Potential Mechanisms.” Alzheimers Dementia, June 2014, S122-S145. Accessed May 22, 2020. https://doi.org/10.1016/j.jalz.2014.04.009.
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Fig. 1: Indiana Prevention Resource Center. Dopamine Reward Pathway. Photograph. Indiana Prevention Resource Center. Accessed May 22, 2020. http://desalledesigns.com/cdesalle/Tobacco1/development/a_04_05_01.html.