I was recently asked to review a new textbook on Nicotine Psychopharmacology, containing 18 very thorough chapters describing the latest evidence on the effects of smoking and nicotine on the brain and behavior. Much of it, though interesting, was a very heavy read. But it occurred to me that it might be useful to try to summarize what the 544 pages in this new book suggests about the effects of nicotine and the reasons smokers get addicted. So here is an attempt to describe how nicotine addiction works, in simplified terms.
When a smoker inhales nicotine from a cigarette, the drug is carried to the brain in highly concentrated form within around 10-15 seconds. The drug then binds to a variety of different types of nicotinic receptors in different parts of the brain, producing psychological and behavioral effects. One of the most important effects is that it stimulates release of dopamine, the ╥reward neurotransmitter╒ in the pleasure center of the brain. This effect appears to be experienced as a subtle ╥satisfaction╙ effect, and causes the smoker to want to smoke again in order to experience the effect. Nicotine has effects on other parts of the brain that effect ╥arousal╙ and the ability to focus our attention and concentration.
Thus smoking a cigarette can help a smoker to think clearly, in ways that are similar to the effects of caffeine. Nicotine also appears to help the smoker form associations between the things they were doing and the situation they were in at the time they were smoking, and the psychological effects of the drug. These learned associations mean that when the smoker is back in a situation in which he or she previously smoked, the brain triggers a memory of the sensations previously experienced and a desire to repeat them. (Often experienced as a desire or craving to smoke).
In addition, the more a person smokes, the more nicotinic receptors grow in his/her brain. Most of these receptors are desensitized when stimulated by nicotine, but when the person stops taking nicotine, more and more of these receptors become sensitized but not activated by nicotine. This leads to effects that are the opposite of the primary effects of nicotine: reduced release of dopamine in the reward center of the brain (experienced as a bad mood), and other effects such as poor concentration and increased appetite caused by lack of the usual nicotine levels in the brain. These symptoms are experienced as unpleasant and prompt the smoker to try to take nicotine (typically by smoking) in order to be able to feel ╥normal╙ again. Thus the abstaining smoker will smoke for a calm and less irritable mood, and to be able to focus their attention without being so distracted by thoughts of smoking or hunger for food.
People differ in the way their body and their brain reacts to nicotine. Many of these differences are influenced by genetic factors, some of which are starting to be understood. For example, some people metabolize nicotine much more quickly than others, meaning that they experience nicotine withdrawal sooner after their last cigarette. Some people are more sensitive to nicotine’s psychological effects and experience withdrawal symptoms more strongly than others.
In addition, there appear to be other substances in cigarette smoke that also have psychological effects. For example, some other substance in cigarette smoke slows down the speed with which dopamine is broken down in the brain. This means that as well as the nicotine causing dopamine to be released, this other substance causes the dopamine to “hang around” in the reward center of the brain a bit longer. For many smokers who try to quit, they experience a relatively brief period of moodiness and cravings, before starting to feel “normal” as a non-smoker.
But for some, stopping smoking produces a more severe withdrawal syndrome, involving a more global loss of satisfaction with life, inability to concentrate, and more severe cravings for a cigarette. These people will find it harder to quit smoking and may obtain greater benefit from use of the FDA-approved smoking cessation medicines.
Here is a link which explains some of these processes in video format: