Previous research provides few clues to
possible biological mechanisms linking smoking
and mental illness. Agonists of nicotinic
cholinergic receptors (including nicotine itself)
presumably improve cognition and mood.55---56
Indeed, these effects of nicotine are the basis
for the self-medication hypothesis regarding
the association of smoking with mental disorders.
14,57 However, it has also been hypothesized
that chronic administration of cholinergic
agents may lead to indirect inhibition of the
nicotinic receptors (functional antagonism) and
hence contribute to increased prevalence of
depression.56 Furthermore, the mechanisms
linking smoking with mental illness may vary
across individuals according to their genetic
makeup.58 The mechanisms may also vary by
type of mental disorder.59 In view of the
findings regarding the moderating effect of age,
exploring the potential impact of biological
factors such as hormonal changes associated
with age may help to elucidate the link between
smoking and mental illness.