Nicotine is one of the most heavily used addictive drugs in the U.S., and smoking cigarettes is the most popular method of using nicotine. Most cigarettes in the U.S. market today contain 10 milligrams (mg) or more of nicotine. The average smoker takes in 1 to 2 mg nicotine per cigarette when inhaling.
In 1989, the Surgeon General issued a report that cigarettes and other forms of tobacco, which contain nicotine (such as cigars, pipe tobacco and chewing tobacco) are addictive. The report also determined that smoking was a major cause of stroke as well as the third leading cause of death in the U.S.
What is nicotine?
Nicotine is one of more than 4,000 chemicals found in the smoke from tobacco products; it is the primary component that acts on the brain. Smokeless tobacco products (for example, snuff and chewing tobacco) also contain many toxins as well as high levels of nicotine. Nicotine is a naturally occurring colorless liquid that turns brown when burned and takes on the odor of tobacco when exposed to air. There are many species of tobacco plants, the tabacum species serving as the major source of today's tobacco products. Extensive study shows it to have a number of complex and sometimes unpredictable effects on the brain and the body.
Nicotine is absorbed through the skin and mucosal lining of the nose and mouth or in the lungs (through inhalation). Nicotine can reach peak levels in the bloodstream and brain rapidly, depending on how it is taken. Cigarette smoking results in nicotine reaching the brain within just 10 seconds of inhalation. However, cigar and pipe smokers, on the other hand, typically do not inhale the smoke, so nicotine is absorbed more slowly through the mucosal membranes of their mouths (as is nicotine from smokeless tobacco).
Nicotine is addictive, which is why most smokers tend to do it regularly. Addiction is characterized by compulsive drug seeking and use, even at the risk of negative health consequences. Most smokers know that tobacco is harmful and express a desire to decrease or end use of it, with nearly 35 million people seriously attempting to quit each year. Unfortunately, most relapse within just a few days, and less than 7 percent of those who try to quit on their own achieve more than a year of abstinence.
Besides nicotine's addictive properties, other factors to consider include its easy availability, the small number of legal and social consequences of tobacco use and the sophisticated marketing and advertising methods of tobacco companies. These combined with nicotine's addictive properties often lead to first use and, ultimately, addiction.
Recent research has shown how nicotine acts on the brain. Nicotine activates the circuitry that regulates feelings of pleasure, the so-called reward pathways. Research has shown that nicotine increases the levels of dopamine (a key brain chemical involved in mediating the desire to consume drugs) in the reward circuits. Nicotine's pharmacokinetic properties have been found 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 within a few minutes, causing the need to continue repeated intake throughout the day.
A cigarette is a very efficient and highly engineered drug-delivery system. A smoker can get nicotine to the brain very rapidly with every inhalation. A typical smoker will take 10 puffs on a lit cigarette over a period of 5 minutes. Thus, a person who smokes about one-and-a-half packs (30 cigarettes) each day gets 300 nicotine hits to the brain daily. These factors contribute considerably to nicotine's highly addictive nature.
Using advanced neuroimaging technology, research is beginning to show that nicotine may not be the only psychoactive ingredient in tobacco. 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 enzyme responsible for breaking down dopamine. The change in MAO must be caused by some tobacco smoke ingredient other than nicotine, since nicotine itself does not dramatically alter MAO levels. The decrease in two forms of MAO, A and B, results in higher dopamine levels. The need to sustain the high dopamine levels results in the desire for repeated drug use.
How does nicotine deliver its effect?
Nicotine acts as both a stimulant and a sedative. Immediately after exposure to nicotine, there is a "kick" caused in part by the drug's stimulation of the adrenal glands and resulting discharge of epinephrine (adrenaline). The rush of adrenaline stimulates the body, causing a sudden release of glucose as well as an increase in blood pressure, heart rate and respiration. Nicotine also suppresses insulin output from the pancreas, causing smokers to be slightly hyperglycemic. In addition, nicotine indirectly causes a release of dopamine in the brain regions that control pleasure and motivation. This reaction is similar to that seen with other abused drugs—such as cocaine and heroin—and is thought to underlie the pleasurable sensations many smokers experience. In contrast, nicotine can also exert a sedative effect, depending on the level of the smoker's nervous system arousal and the dose of nicotine taken.
Repeated exposure to nicotine results in the development of tolerance, the condition in which higher doses of a drug are required to produce the same initial effect. Nicotine is metabolized fairly rapidly, disappearing from the body in a few hours. Therefore some tolerance is lost overnight, and smokers often report that the first cigarettes of the day are the strongest and/or the "best." Tolerance progresses as the day develops, and later cigarettes have less effect.
Cessation of nicotine
Cessation of nicotine use is followed by a withdrawal period that may last a month or more and includes symptoms that can quickly drive people back to tobacco use. Nicotine withdrawal symptoms may begin within a few hours after the last cigarette, and include irritability, sleep disturbances, craving, cognitive and attentional deficits and increased appetite. Symptoms generally peak within the first few days and may subside within a few weeks, though for some people, they may persist for months or longer.
An important and poorly understood component of the nicotine withdrawal syndrome is craving, an urge for nicotine that has been described as a major obstacle to successful abstinence and may persist for 6 months or longer. While the withdrawal syndrome is related to the pharmacological effects of nicotine, the severity of withdrawal symptoms can also be affected by psychological experiences. For some people, the feel, smell and sight of a cigarette and the ritual of obtaining, handling, lighting and smoking it are all associated with the pleasurable effects of smoking and can make withdrawal or craving worse. While nicotine gum and patches may alleviate the pharmacological aspects of withdrawal, cravings often persist.
What are the medical consequences?
The medical consequences of nicotine exposure result from effects of both the nicotine itself and how it is taken. Tobacco use accounts for one-third of all cancers. Foremost among the cancers caused by tobacco is lung cancer—the number one cancer killer of both men and women. In 90 percent of all lung cancer cases, there is a link to cigarette smoking.
Smoking also causes lung diseases such as chronic bronchitis and emphysema, and it exacerbates asthma symptoms in adults and children. Smoking is also associated with cancers of the mouth, kidney, esophagus, pharynx, larynx, stomach, pancreas, cervix, ureter and bladder. The overall rates of death from cancer are twice as high for smokers than nonsmokers, with heavy smokers having a four-time-greater rate than nonsmokers.
It has been well documented that smoking significantly increases the risk of heart disease, including stroke, vascular disease, heart attack and aneurysm. It is estimated that nearly one-fifth of deaths from heart disease are caused by smoking.
While we tend to only think of medical consequences that result from direct use of tobacco, passive or secondary smoke also increases the risk for many diseases. Environmental tobacco smoke (ETS) is a major source of indoor air contaminants; secondhand smoke is estimated to cause approximately 3,000 lung cancer deaths per year among nonsmokers and contributes to as many as 40,000 deaths related to cardiovascular disease. Exposure to tobacco smoke in the home increases the severity of asthma for children and is a risk factor for new cases of childhood asthma. ETS exposure has been linked with sudden infant death syndrome. Additionally, dropped cigarettes are the leading cause of residential fire fatalities, leading to more than 1,000 such deaths each year.
At higher doses, such as that found in some insecticide sprays, nicotine can be extremely toxic, causing vomiting, convulsions, tremors and death. Nicotine poisoning has been reported from accidental ingestion of insecticides and ingestion of tobacco products by children. Death usually results in a few minutes from respiratory failure caused by paralysis.
Laboratory research indicates that cigarette smoking has toxic effects on the cardiovascular system. For this reason, nicotine replacement medicines such as nicotine gum and the patch have been extensively evaluated for cardiovascular toxicity, especially for patients with cardiac disease. These experiments suggest that use of nicotine replacements for smoking cessation does not increase cardiovascular risk. These findings are consistent with the generally slower and lower doses of nicotine obtained from the medicines as compared to tobacco products, and to the absence of carbon monoxide and numerous other toxins in tobacco smoke.
Women who smoke generally have earlier menopause. Women who smoke cigarettes and also take oral contraceptives are more prone to cardiovascular and cerebrovascular diseases than are other smokers.
Pregnant cigarette smokers run an increased risk of having stillborn or premature infants or infants with low birth weight. Children of women who smoked while pregnant have an increased risk for developing conduct disorders.
The Environmental Protection Agency has concluded that secondhand smoke causes lung cancer in adults and greatly increases the risk of respiratory illnesses in children and sudden infant death.
