Smoking and mental health - NCSCT

Neurobiological and behavioural mechanisms linking smoking and mental disorders 3
Although it is clear that nicotine has the neurobiological and behavioural
properties of a drug of dependence, when compared with many drugs of
dependence used illicitly its reinforcing properties are weak and appear
insufficient to account for the powerful dependence on tobacco experienced
by most habitual smokers. 15 Furthermore, the therapeutic nicotine
preparations commonly used to aid cessation are neither strongly effective in
this regard nor commonly subject to abuse. These observations have led to the
conclusion that the tobacco smoke vehicle, through which most people dose
themselves with nicotine, may also play an important part in addiction to
tobacco smoking.
There are a number of components of tobacco smoke that could enhance the
addictive properties of nicotine. Some of these inhibit the enzyme monoamine
oxidase, which metabolises dopamine in the brain, thereby enhancing the
rewarding effects evoked by release of this monoamine. 16–18 Studies in
experimental animals have confirmed that inhibition of monoamine oxidase
potentiates nicotine self-administration. 19–21 Other studies have focused on the
role of non-pharmacological factors such as environmental or conditioned
stimuli associated with the delivery of nicotine, both of which significantly
enhance self-administration of nicotine. 22–24 Sensorimotor stimuli also seem to
be important factors in the development of tobacco dependence, 25 particularly
among highly dependent smokers. 26 These observations have led Rose 27 to
suggest that non-nicotinic factors play a pivotal role in tobacco dependence.
Similarly, these and other results have led Caggiula and colleagues 28 to propose a
dual reinforcement model of tobacco dependence that relies on both the primary
reinforcing properties of nicotine itself, and enhancement by nicotine of the
reinforcing salience of other sensory or contextual stimuli, paired with the
delivery of the drug.
3.2 Models of association and sources of evidence
One possible mechanism of association between smoking and mental disorders is
the self-medication model, whereby smoking is used to alleviate symptoms,
particularly those of negative affect and impaired cognition, 29,30 eg individuals
with negative affect may turn to substance use, including tobacco, to alleviate
emotional distress, 29 whereas individuals with attentional and learning deficits
may use tobacco to help them overcome these limitations. Cultural and social
beliefs, eg a belief that smoking is an effective anxiolytic or antidepressant, even
in the absence of a true effect, may also contribute to this process. Alternatively,
smoking could be a causal risk factor for the development of mental illness,
although it is also possible that the association is due to confounding by other
factors, eg genetic traits, that independently influence both smoking and mental
illness. In addition it is possible that the nature of the association changes with
chronicity of exposure.
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