Nicotine and Tobacco
Welcome back! In the last lesson, we discussed alcohol, the drug that creates the most overall societal harm. In today’s lesson, we are going to cover nicotine and tobacco, the drug that is the leading cause of preventable death. According to the Centers for Disease Control and Prevention, approximately half a million Americans die each year from smoking. Many of these deaths are premature. When you take into account the sheer number of smokers and their lifetime risk of disease, nicotine, and tobacco could be considered the deadliest drug used by humans.
There are a number of tobacco plant varieties, but the most commonly cultivated is Nicotiana tabacum. The tobacco plant contains approximately 4,000 chemicals, including the primary psychoactive constituent nicotine. The nicotine in tobacco can be administered in numerous ways. The first, and by far the most common route, is inhaling tobacco smoke from cigarettes. The tobacco leaf is dried and fermented and then prepared for cigarettes, cigars, pipes, and hookah. Other routes of administration include chewing tobacco, dry snuff (snorted into the nose), moist snuff (placed between the lip and gums), and snus. Snus is a tobacco product resembling a small teabag. It is placed behind the upper lip typically. In Sweden, snus is very popular and used by more people than cigarettes.
Electronic cigarettes or vaping is the newest form of nicotine administration. Vaping involves heating both nicotine and flavoring additives in a device (e.g., tank, pen, mods) to create an aerosol that is then inhaled by the user. It is a very efficient way to deliver nicotine, second only to tobacco smoke. The evidence suggests that vaping is likely safer than smoking as the latter deposits tar on the surface of the lungs and irritates tissues. However, this doesn’t mean that vaping is entirely safe. There are growing reports of lung injuries and a syndrome called e-cigarette, or vaping, product use associated lung injury (EVALI) occurring in people who regularly vape. In addition, there are serious concerns that young people who vape will not only become addicted to vaping but also later transition to smoking tobacco.
When tobacco is smoked, or nicotine is vaped, drug particles are deposited onto the surface of the lungs. Nicotine is then rapidly absorbed through the lung tissue and into the bloodstream. Smoking a single cigarette results in the absorption of one to two mg of nicotine. Newer generation vaping devices result in nicotine absorption that is similar to cigarettes. In contrast, the nicotine from oral methods like snus is absorbed through buccal membranes in the mouth. Once in the bloodstream, nicotine is carried to the heart and then to the brain.
After nicotine reaches the brain, it binds with nicotinic acetylcholine receptors (nAChRs). When this happens, it mimics acetylcholine, a neurotransmitter that plays an important role in contracting muscles, dilating blood vessels, and regulating heart rate. When nicotine stimulates nAChRs in the reward center of the brain, it results in an increase in dopamine and related feelings of euphoria. Furthermore, another chemical in tobacco interferes with the breakdown of dopamine, leaving more available in the brain. In daily smokers, continued use of tobacco throughout the day helps to keep nicotine levels in the blood relatively constant.
Nicotine has a half-life of roughly two hours. Half-life refers to the time it takes for the amount of drug in the body to be reduced by 50%. As such, heavy smokers will often feel the craving to have a cigarette every hour or so to replenish nicotine levels. Not surprisingly, the first cigarette in the morning is often the most pleasurable due to not being able to smoke while sleeping. Eventually, tolerance to nicotine develops, and smokers feel less pleasure from smoking. However, nicotine use also leads to the upregulation of nicotinic receptors; in other words, more receptors are available in the brain. The result is stronger cravings for nicotine. Any smoker will tell you that the first couple of weeks of attempting to quit can be especially difficult, which is largely due to these brain changes.
Acute effects. Tobacco and nicotine have several immediate effects. First, smoking a cigarette affects mood. Nicotine is known to increase feelings of calmness. Part of this is likely due to relief from withdrawal symptoms. Nicotine can also alter cognitive functioning. For instance, it can enhance attention and memory on some tasks. However, this could also be because nicotine brings people back to baseline on these tasks after experiencing withdrawal effects.
Chronic effects. Tobacco is associated with many long-term health effects. It remains the leading cause of preventable death. Smoking can increase the risk of heart disease by roughly 50% and is the cause of at least 80% of chronic obstructive pulmonary disease (COPD) cases. It is also directly attributable to approximately 30% of cancers. Finally, secondhand smoke remains a severe cause of disease for non-smokers that are exposed to it.
Addiction potential. The addiction potential of nicotine is very high, especially when smoked. The withdrawal symptoms are very uncomfortable and include irritated mood, problems concentrating, and strong cravings. The vast majority of smokers want to quit, but any single quit attempt is successful just 10% of the time. There are some good treatments available. Nicotine replacement therapy (e.g. nicotine gum) doubles the success rate (~20%), and other medications, including Bupropion and Varenicline are also effective. Lastly, vaping has been popularized as a way to quit smoking. Recent studies have found that vaping can be helpful; however, it is not recommended as a first-line treatment for smoking addiction.
That’s it for today; in tomorrow’s lecture, we will move on to cannabis. See you then!
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