Nicotine is highly addictive. Most smokers use tobacco regularly because they are addicted to nicotine. Addiction is characterized by compulsive drug seeking and use, even in the face of negative health consequences, and tobacco use certainly fits the description. It is well documented that most smokers identify tobacco as harmful and express a desire to reduce or stop using it, and nearly 35 million of them make a serious attempt to quit each year. Unfortunately, less than 7 percent of those who try to quit on their own achieve more than 1 year of abstinence; most relapse within a few days of attempting to quit.
Other factors to consider besides nicotine's addictive properties include its high level of availability, the small number of legal and social consequences of tobacco use, and the sophisticated marketing and advertising methods used by tobacco companies. These factors, combined with nicotine's addictive properties, often lead to first use and, ultimately, nicotine addiction.
Recent research has shown in fine detail how nicotine acts on the brain to produce a number of behavioral effects. Of primary importance to its addictive nature are findings that nicotine activates the brain circuitry that regulates feelings of pleasure, the so-called reward pathways. A key brain chemical involved in mediating the desire to consume drugs is the neurotransmitter dopamine, and research has shown that nicotine increases the levels of dopamine in the reward circuits. Nicotine's pharmacokinetic properties have been found also to enhance its abuse potential. Cigarette smoking produces a rapid distribution of nicotine to the brain, with drug levels peaking within 10 seconds of inhalation. The acute effects of nicotine dissipate in a few minutes, causing the smoker to continue dosing frequently throughout the day to maintain the drug's pleasurable effects and prevent withdrawal.
What people frequently do not realize is that the cigarette is a very efficient and highly engineered drug-delivery system. By inhaling, the smoker can get nicotine to the brain very rapidly with every puff. A typical smoker will take 10 puffs on a cigarette over a period of 5 minutes that the cigarette is lit. Thus, a person who smokes about 1-1/2 packs (30 cigarettes) daily, gets 300 "hits" of nicotine to the brain each day. These factors contribute considerably to nicotine's highly addictive nature.
Scientific research is also beginning to show that nicotine may not be the only psychoactive ingredient in tobacco. Using advanced neuroimaging technology, scientists can see the dramatic effect of cigarette smoking on the brain and are finding a marked decrease in the levels of monoamineoxidase (MAO), an important enzyme that is responsible for breaking down dopamine. The change in MAO must be caused by some tobacco smoke ingredient other than nicotine, since we know that nicotine itself does not dramatically alter MAO levels. The decrease in two forms of MAO, A and B, then results in higher dopamine levels and may be another reason that smokers continue to smoke—to sustain the high dopamine levels that result in the desire for repeated drug use.