Tobacco Addiction: Nicotine and Other Factors, Animation

(USMLE topics) Nicotine and other factors contributing to tobacco addiction: other substances, genetics, behaviors, types of tobacco products and the way they are consumed. Harmful effects of smoking, including during pregnancy, treatment for addiction.

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Nicotine is the major substance responsible for tobacco addiction. Nicotine acts to increase the amount of a neurotransmitter called dopamine in the brain reward pathway, which is designed to “reward” the body with pleasurable feelings for important behaviors that are essential for survival, such as feeding when hungry. Chronic tobacco use produces repeated dopamine surges which eventually desensitize the reward system, making it less responsive to everyday stimuli. As the body adapts to constant high levels of dopamine, more and more nicotine is required to achieve the same pleasurable effect, and smoking cessation can produce withdrawal symptoms.
But nicotine is not the only substance to blame for tobacco addiction. At least another major constituent of tobacco smoke, acetaldehyde, is found to reinforce nicotine dependence, notably in adolescents. This may explain why teens are more vulnerable to tobacco addiction. In fact, most smokers started when they were teens.
Genetic makeup also plays a role in susceptibility to addiction. Some people are more prone to dependence than others when exposed to nicotine; and once addicted, less able to quit. Many genes are likely to be involved. What is inherited is perhaps the extent the brain responds to nicotine, and the rate of nicotine clearance. For example, people who metabolize nicotine more slowly tend to smoke fewer cigarettes a day and can generally quit with less effort.
The development of tobacco addiction depends on the speed and the amount of nicotine absorbed by the brain. Cigarette smoking delivers nicotine to the brain within seconds of smoke inhalation, resulting in immediate rewarding effects. Cigar smokers who inhale absorb nicotine as quickly as cigarette smokers. Those who don’t inhale absorb more slowly, through the lining of the mouth, but the amount of nicotine can be greater depending on the cigar size. Chewing on smokeless tobacco products delivers nicotine more slowly than smoking, but the blood levels of nicotine can be much the same.
There are behavioral factors that reinforce addiction. Behavioral factors may be as important to tobacco addiction as the action of nicotine itself.
Tobacco use is a leading cause of premature death. Smoking is associated with lung diseases and cancers, increases risks for cardiovascular diseases such as heart attacks and strokes. Smoking during pregnancy may deprive the fetus of oxygen and cause fetal growth retardation. Nicotine can cross the placenta to fetal circulation and cause withdrawal symptoms in infants. Smoking during pregnancy is also associated with increased infant deaths, as well as learning and behavioral problems in children.
Treatment for tobacco addiction usually consists of behavioral therapies combined with nicotine replacement such as nicotine patch and gums. The use of medicinal nicotine with low addiction potential helps alleviate withdrawal symptoms, while also reducing toxicity associated with other harmful substances in tobacco products and cigarette smoke.