Smoking, nicotine and psychiatric disorders: evidence for therapeutic role, controversies and implications for future research.

Researchers interested in investigating the possible therapeutic effects and the mechanisms of action of nicotine in neuropsychiatric disorders face a social-scientific-ethical dilemma. This dilemma comprises three components: (1) the known addictive potential of nicotine makes careful evaluation of the therapeutic potential of this compound socially unattractive; (2) the potential misuse of scientifically determined data by the tobacco 'lobby' creates ethical concerns; and (3) the possible confusion between the differential effects of nicotine in human smokers versus non-smokers creates difficulties in study designs in voluntary human subjects. Therefore, it is imperative that, at the onset of this review, the authors stress that they do not advocate cigarette-smoking as a route of nicotine intake under any circumstances on the basis that controlled dosing of nicotine may be of potential benefit in some neuropsychiatric disorders. In this article, we review the psychopharmacology of nicotine and its effects in a variety of neuropsychiatric disorders including schizophrenia, depression, anxiety and Tourette's syndrome. Possible mechanisms of action of nicotine directly or indirectly via its interaction with other neurotransmitter systems (i.e. serotonin, dopamine and noradrenaline) in relation to its potential role in these disorders are discussed. It is postulated that new drugs may need to be developed that selectively interact with nicotinic receptors without addiction potential.