Nicotine addiction

Nicotine has come to be regarded as a highly addic-
tive substance. Judging by the current diagnostic cri-
teria, tobacco dependence appears to be quite preva-
lent among cigarette smokers; more than 90% of
smokers meet the DSM-IV (Diagnostic and Statisti-
calManual ofMental Disorders) criteria for nicotine
dependence [76]. Research has shown that nico-
tine acts on the brain to produce a number of ef-
fects [77,78] and immediately after exposure, nico-
tine induces a wide range of central nervous sys-
tem, cardiovascular, and metabolic effects. Nicotine
stimulates the release of neurotransmitters, in-
ducing pharmacologic effects, such as pleasure
and reward (dopamine), arousal (acetylcholine,
norepinephrine), cognitive enhancement (acetyl-
choline), appetite suppression (norepinephrine),
learning and memory enhancement (glutamate),
mood modulation and appetite suppression (sero-
tonin), and reduction of anxiety and tension
(β-endorphin and GABA) [78]. Upon entering the
brain, a bolus of nicotine activates the dopamine re-
ward pathway, a network of nervous tissue in the
brain that elicits feelings of pleasure and stimulates
the release of dopamine.
Although withdrawal symptoms are not the only
consequence of abstinence, most cigarette smok-
ers do experience craving and withdrawal on ces-
sation [79], and, therefore, relapse is common [80].
The calming effect of nicotine reported by many
users is usually associated with a decline in with-
drawal effects rather than direct effects on nicotine
[53]. This rapid dose-response, along with the short
half-life of nicotine (t1 / 2 = 2 h), underlies tobacco
users’ frequent, repeated administration, thereby
perpetuating tobacco use and dependence. Tobacco
users become proficient in titrating their nicotine
levels throughout the day to avoid withdrawal
symptoms, to maintain pleasure and arousal, and
to modulate mood. Withdrawal symptoms include
depression, insomnia, irritability/frustration/anger,
anxiety, difficulty concentrating, restlessness, in-
creased appetite/weight gain, and decreased heart
rate [81,82].
The assumption that heavy daily use (i.e., 15–
30 cigarettes per day), is necessary for dependence
to develop is derived from observations of “chip-
pers,” adult smokers who have not developed de-
pendence despite smoking up to five cigarettes per
day for many years [83,84]. Chippers do not tend
to differ from other smokers in their absorption and
metabolism of nicotine, causing some investigators
to suggest that this level of consumptionmay be too
low to cause nicotine dependence. However, these
atypical smokers are usually eliminated from most
studies, which are routinely limited to smokers of
at least 10 cigarettes per day [83].
Signs of dependence on nicotine have been re-
ported among adolescent smokers, with approx-
imately one fifth of them exhibiting adult-like
dependence [85]. Although, lengthy and regular
tobacco use has been considered necessary for
nicotine dependence to develop [68], recent re-
ports have raised concerns that nicotine depen-
dence symptoms can develop soon after initiation,
and that these symptoms might lead to smoking
intensification [79,86]. Adolescent smokers, who
use tobacco regularly, tend to exhibit high craving
for cigarettes and substantial levels of withdrawal
symptoms [87].