"Things we should Know"
Cigarettes and Other Nicotine Products
Cigarette smoking has been the most popular method of taking
nicotine since the beginning of the 20th century. In 1989, the U.S. Surgeon General issued
a report that concluded that cigarettes and other forms of tobacco, such as cigars, pipe
tobacco, and chewing tobacco, are addictive and that nicotine is the drug in tobacco that
causes addiction. In addition, the report determined that smoking was a major cause of
stroke and the third leading cause of death in the United States.
Nicotine is highly addictive. It is both a stimulant and a sedative
to the central nervous system. The ingestion of nicotine results in an almost immediate
"kick" because it causes a discharge of epinephrine from the adrenal cortex.
This stimulates the central nervous system, and other endocrine glands, which causes a
sudden release of glucose. Stimulation is then followed by depression and fatigue, leading
the abuser to seek more nicotine.
Nicotine is absorbed readily from tobacco smoke in the lungs, and it
does not matter whether the tobacco smoke is from cigarettes, cigars, or pipes. Nicotine
also is absorbed readily when tobacco is chewed. With regular use of tobacco, levels of
nicotine accumulate in the body during the day and persist overnight. Thus, daily smokers
or chewers are exposed to the effects of nicotine for 24 hours each day. Nicotine taken in
by cigarette or cigar smoking takes only seconds to reach the brain but has a direct
effect on the body for up to 30 minutes.
Research has shown that stress and anxiety affect nicotine tolerance
and dependence. The stress hormone corticosterone reduces the effects of nicotine;
therefore, more nicotine must be consumed to achieve the same effect. This increases
tolerance to nicotine and leads to increased dependence. Studies in animals have also
shown that stress can directly cause relapse to nicotine self-administration after a
period of abstinence.
Other studies have shown that animals cannot discriminate between
the effects of nicotine and the effects of cocaine. Studies have also shown that nicotine
self-administration sensitizes animals to self-administer cocaine more readily.
Addiction to nicotine results in withdrawal symptoms when a person
tries to stop smoking. For example, a study found that when chronic smokers were deprived
of cigarettes for 24 hours, they had increased anger, hostility, and aggression, and loss
of social cooperation. Persons suffering from withdrawal also take longer to regain
emotional equilibrium following stress. During periods of abstinence and/or craving,
smokers have shown impairment across a wide range of psychomotor and cognitive functions,
such as language comprehension.
Women who smoke generally have earlier menopause. If women smoke
cigarettes and also take oral contraceptives, they are more prone to cardiovascular and
cerebrovascular diseases than are other smokers; this is especially true for women older
Pregnant women who smoke cigarettes run an increased risk of having
stillborn or premature infants or infants with low birthweight. Children of women who
smoked while pregnant have an increased risk for developing conduct disorders. National
studies of mothers and daughters have also found that maternal smoking during pregnancy
increased the probability that female children would smoke and would persist in smoking.
Adolescent smokeless tobacco users are more likely than nonusers to
become cigarette smokers. Behavioral research is beginning to explain how social
influences, such as observing adults or other peers smoking, affect whether adolescents
begin to smoke cigarettes. Research has shown that teens are generally resistant to many
kinds of anti-smoking messages.
In addition to nicotine, cigarette smoke is primarily composed of a
dozen gases (mainly carbon monoxide) and tar. The tar in a cigarette, which varies from
about 15 mg for a regular cigarette to 7 mg in a low-tar cigarette, exposes the user to a
high expectancy rate of lung cancer, emphysema, and bronchial disorders. The carbon
monoxide in the smoke increases the chance of cardiovascular diseases.
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.
Research has shown that nicotine, like cocaine, heroin, and
marijuana, increases the level of the neurotransmitter dopamine, which affects the brain
pathways that control reward and pleasure. Scientists now have pinpointed a particular
molecule (the beta 2 subunit of the nicotine cholinergic receptor) as a critical component
in nicotine addiction. Mice that lack this molecule fail to self-administer nicotine,
implying that without the b2 molecule, the mice do not experi ence the positive
reinforcing properties of nicotine. This new finding identifies a potential site for
targeting the development of anti-nicotine addiction medications.
Other new research found that individuals have greater resistance to
nicotine addiction if they have a genetic variant that decreases the function of the
enzyme CYP2A6. The decrease in CYP2A6 slows the breakdown of nicotine and protects
individuals against nicotine addiction. Understanding the role of this enzyme in nicotine
addiction gives a new target for developing more effective medications to help people stop
smoking. Medications might be developed that can inhibit the function of CYP2A6, thus
providing a new approach to preventing and treating nicotine addiction.
Another study found dramatic changes in the brain's pleasure
circuits during withdrawal from chronic nicotine use. These changes are comparable in
magnitude and duration to similar changes observed during the withdrawal from other abused
drugs such as cocaine, opiates, amphetamines, and alcohol. Scientists found significant
decreases in the sensitivity of the brains of laboratory rats to pleasurable stimulation
after nicotine administration was abruptly stopped. These changes lasted several days and
may correspond to the anxiety and depression experienced by humans for several days after
quitting smoking "cold turkey." The results of this research may help in the
development of better treatments for the withdrawal symptoms that may interfere with
individual's attempts to quit smoking.
Research suggests that smoking cessation should be a gradual process
because withdrawal symptoms are less severe in those who quit gradually than in those who
quit all at once. Rates of relapse are highest in the first few weeks and months and
diminish considerably after 3 months.
Studies have shown that pharmacological treatment combined with
psychological treatment, including psychological support and skills training to overcome
high-risk situations, results in some of the highest long-term abstinence rates.
Behavioral economic studies find that alternative rewards and
reinforcers can reduce cigarette use. One study found that the greatest reductions in
cigarette use were achieved when smoking cost was increased in combination with the
presence of alternative recreational activities.
Nicotine chewing gum is one medication approved by the Food and Drug
Administration (FDA) for the treatment of nicotine dependence. Nicotine in this form acts
as a nicotine replacement to help smokers quit the smoking habit. The success rates for
smoking cessation treatment with nicotine chewing gum vary considerably across studies,
but evidence suggests that it is a safe means of facilitating smoking cessation if chewed
according to instructions and restricted to patients who are under medical supervision.
Another approach to smoking cessation is the nicotine transdermal
patch, a skin patch that delivers a relatively constant amount of nicotine to the person
wearing it. A research team at NIDA's Division of Intramural Research studied the safety,
mechanism of action, and abuse liability of the patch that was consequently approved by
FDA. Both nicotine gum and the nicotine patch are adjuncts to nicotine cessation programs
and are used to help people achieve abstinence, reduce withdrawal symptoms, and prevent
relapse while undergoing behavioral treatment.
Much of the information in this
section comes from the US National Institute of Drug Abuse. Material on Australian studies
will be made available soon.