Substance Use Disorders 395
Nicotine
Nicotine—the active ingredient in tobacco—is a stimulant that leads to abuse and
dependence and tobacco use is associated with cancer. When inhaled via cigarettes,
nicotine is absorbed into the lungs. Nicotine can also be absorbed through the
mucus membranes in the mouth and throat when chewed (chewing tobacco) or
when smoked but not inhaled (pipe or cigar tobacco). Nicotine causes increased
alertness, but also dizziness, increased blood pressure, and irritability. Cigarette
smoking delivers not only nicotine into the smoker’s bloodstream, but also carbon
monoxide and tar to the lungs; chronic smokers have a higher risk of developing
lung cancer and other breathing-related problems than do people who do not smoke
(NIDA,2007a). According to the National Institute of Drug Abuse (NIDA, 2006c),
tobacco abuse and dependence is the number-one preventable cause of death in the
United States: Almost half a million Americans die each year as a result of cigarette
smoking. The health effects of cigarette smoking are also costly: $75 billion is spent
annually in the United States on related health care costs (NIDA, 2006c).
Nicotine withdrawal symptoms often include insomnia, anxiety, irritability, andconcentration problems (Baker, Brandon, & Chassin, 2004). People who have nico-
tine dependence may report that the drug makes them feel relaxed. However, this
may not be a direct effect of nicotine: Rather, when enough hours have elapsed since
the last “hit” of nicotine, the dependent person may begin to have withdrawal symp-
toms, which include becoming irritable—and having another cigarette or wad of
chewing tobacco produces the experience of “relaxation” as the irritability and jit-
teriness of withdrawal fade (NIDA, 2006c).
Many smokers try to quit several times before they are successful. George Har-rison quit for a while but then resumed smoking until he was diagnosed with a
smoking-related cancer, at which point he quit for good. Nicotine dependence can
be so powerful that some people who develop smoking-related cancer continue the
habit even after the cancer is diagnosed.
Understanding Paraphilias
Each type of psychoactive substance can change the way the neurons function in specifi c
brain areas. Depending on the substance, as well as the dose and the frequency of use,
these brain changes can lead use to evolve into abuse and dependence. In turn, abuse
and dependence can alter the way neurons communicate with each other and the ways
various brain areas function and interact. With some substances, these changes may be
permanent. In the following sections we examine how neurological factors contribute
to stimulant abuse and stimulant dependence (and substance abuse more generally),
again considering brain systems and neural communication. Because very little is known
about how genes might infl uence stimulant abuse, that factor will not be considered.
We’ll begin by discussing the role of dopamine, which plays an important role with vir-
tually all stimulants but especially with cocaine and methamphetamine. But dopamine
isn’t the whole story, as we shall see; we’ll also consider additional general mechanisms
and examine the bases of abuse of two particular substances: MDMA and nicotine.
However, keep in mind that the major brain systems involved in substance abuse are
not independent—they constantly infl uence each other through feedback loops, and
these loops are probably at least as important as each system’s individual contributions.
Brain Systems and Neural Communication I: Dopamine and Abuse
Particular brain structures have a role in stimulant abuse largely because of the
effects of specifi c neurotransmitters, and so we consider brain systems and neural
communication together.
The Dopamine Reward System
Dopamine plays a key role in both the pleasurable experience of taking stimulants and
the abuse of stimulants (Kalivas & Volkow, 2005), as well as in the abuse of many
other psychoactive substances. To see how, we need to consider the neural circuits that
Although all the Beatles smoked cigarettes
during their teenage years, some of them
continued to smoke. George Harrison (at right)
smoked heavily for almost all of his adult life, up
to the point where he was diagnosed with throat
cancer, in 1998. He also developed lung cancer,
which led to his death in 2001.DAVID MAGNUS/Rex Features courtesy Everett Collection