Tobacco and Public Health - TCSC Indonesia

BRIDGETTE E. GARRETT ET AL. 151
However, even though cigarette smoking is the most common way for smokers to
self-administer nicotine in the laboratory setting, the intravenous route of nicotine
administration has also been used to demonstrate nicotine reinforcement in humans
(Henningfield et al. 1983), confirming the importance of nicotine in tobacco reinforcement
and addiction. This study showed that smokers will lever-press to selfadminister
intravenous nicotine in place of cigarettes. In this procedure, subjects were
allowed to choose between nicotine and placebo and they preferentially chose nicotine,
clearly demonstrating its positive reinforcing effects. Two important conclusions from
the Henningfield et al. study are (1) intravenous nicotine self-administration in humans
produced euphoric effects similar to those produced by morphine and cocaine, two typically
abused drugs with powerful reinforcing effects, and (2) intravenous nicotine selfadministration
in humans is a viable method for measuring nicotine reinforcement, as
patterns resembled those of humans smoking cigarettes and animals self-injecting psychomotor
stimulants under similar experimental conditions.
There are several factors that can influence nicotine self-administration including
the availability of nicotine, concurrent drug use, and environmental and social factors,
but the primary factor that influences nicotine self-administration is the speed of
nicotine delivery. When tobacco smoke is inhaled, nicotine is rapidly absorbed into
the lungs, enters the arterial circulation and is rapidly distributed to body tissues
(Benowitz 1996; Henningfield et al. 1993). Following tobacco smoke inhalation,
nicotine reaches the brain within a matter of seconds, thus contributing to the
powerful reinforcing effects of the cigarette. The importance of speed in nicotine reinforcement
is further evidenced by the fact that therapeutic forms of nicotine, such as
the gum and patch, are generally not addictive because of the slow speed with which
they deliver nicotine to the brain, typically taking many minutes or even hours
(Henningfield and Keenan 1993).
Nicotine is also self-administered to avoid unpleasant withdrawal effects (i.e. negative
reinforcement) which (frequently?) occur after abrupt cessation or reduction of
nicotine in the individual who has become physically dependent on it. Physical
dependence results when chronic administration of the drug alters the physiology and
behavior in such a way that physical and behavioral functioning are disrupted when
drug intake is abruptly reduced (O’Brien 1996; US DHHS 1988). The nicotine
withdrawal syndrome is characterized by: dysphoric or depressed mood; insomnia;
irritability, frustration, or anger; anxiety; difficulty concentrating; restlessness;
decreased heart rate; increased appetite or weight gain (American Psychiatric
Association 1994). Although tobacco users acquire preferences for particular types of
tobacco products, and even for particular brands within types of products, the withdrawal
syndrome can be at least partially relieved by a wide range of nicotine delivery
forms including, for example, the substitution of chewing tobacco for cigarettes, or the
administration of nicotine in the form of gum, patches, or intravenous injections
(US DHHS 1988; O’Brien 1996).