The tobacco in cigarettes contains compounds known to cause functional and structural changes to the brain, making smoking addictive. When someone smokes, brain chemistry is fundamentally altered and smoking becomes habit forming through repeated sessions as the brain adjusts to the changes in its chemistry. Quitting smoking can be challenging as a result of the fact that the body develops a dependence on the chemicals in tobacco and the patient experiences withdrawal symptoms as the brain attempts to readjust.
Nicotine, a compound found in tobacco that mimics the actions of the neurotransmitter acetylcholine in the body, is the key thing that makes smoking addictive. When nicotine enters the brain, it binds to acetylcholine receptors and people experience a cascade of neurological responses, including increased alertness and focus. Over time, regular smoking causes the brain to think that acetylcholine levels are unusually high and in response, it grows more receptors for this neurotransmitter.
The increased number of receptors decreases sensitivity to acetylcholine and nicotine, as more is needed to get the same response. This can stimulate people into smoking more, thus causing the brain to react by making more receptors and creating an endless cycle, explaining what makes smoking addictive. When people stop smoking, they have increased numbers of acetylcholine receptors, but these receptors are not being stimulated. The patient experiences withdrawal as the brain copes with the normal level of acetylcholine in the body.
Neurologists have studied the impact of smoking on the brain extensively to learn more about what makes smoking addictive and how smoking changes long-term brain function and structure. Some of these studies were suppressed by tobacco companies concerned about the impact on sales that disclosures of health effects, including addiction, could have. When studies informing the public that smoking is addictive were finally released, the public response was explosive in some regions of the world.
Smoking is not only addictive, it also appears to be one of the stronger addictive substances used by human beings. People who have experienced dependency on multiple substances have noted that tobacco products are among the most difficult to quit. Because smoking is addictive and hard to stop, many public outreach programs focus on preventing people from taking up smoking habits in the first place, with the goal of reducing the incidence of diseases related to smoking in the population. There are clear links between smoking and a number of serious medical complications including cancers and cardiovascular disease.