Шизофрения и курение

The self-medication hypothesis of smoking in schizophrenia

There is a discrepancy in the literature, with numerous animal studies suggesting that nicotine should help negative symptoms but scarce clinical data suggesting that this may be true in those with schizophrenia (Hughes, 2000). Two main sub-hypotheses are usually included in the self-medication hypothesis: smoking reduces the side-effects of antipsychotics; and nicotine may improve schizophrenic symptoms, particularly the negative, cognitive and/or depressive symptoms (Taiminen et al, 1998).

Two mechanisms have been implicated in the reduction of antipsychotic side-effects: a release of dopamine resulting from the administration of nicotine, a notion supported by both acute administration of nicotine in animal models (Drew et al, 2000) and in vivo human studies (Salokangas et al, 2000); and a decrease in antipsychotic blood levels through enzymatic induction. Individuals with schizophrenia who smoke tend to receive consistently higher doses of antipsychotics than non-smokers (Ziedonis et al, 1994; de Leon et al,1995, 2002a). The inductive effect of smoking in antipsychotic metabolism therefore is inadvertently corrected by psychiatrists, because smokers tend to be treated with higher daily doses of antipsychotics than non-smokers. When compared with others with severe mental illness in three epidemiological studies in psychiatric hospitals, the effect of antipsychotic medication did not explain the association between schizophrenia and smoking (de Leon et al,1995, 2002a; Llerena et al, 2003). Some cross-sectional studies have suggested that smoking reduces antipsychotic side-effects and others have not (Dalack et al, 1998); yet all of these studies are hampered by the lack of control for confounding factors. Longitudinal studies with small samples suggest that, when compared with atypical antipsychotics, typical antipsychotics are associated with increased smoking in some individuals (McEvoy et al, 1995) and with a greater difficulty for quitting smoking (Georgeet al, 2000). Anticholinergic medication was not associated significantly with smoking in this or in previous studies (de Leon et al, 1995, 2002a, b).

In spite of the hypothesis from animal studies (Drew et al, 2000), very limited clinical data support an association between smoking and a reduction in negative symptoms (Dalack et al, 1998). Data indicating that nicotine may improve sensory gating abnormalities and smooth pursuit eye movements in schizophrenia or cognitive abnormalities induced by antipsychotics are somewhat stronger. Nicotine may have antidepressant qualities in individuals with depression (Salin-Pascual et al, 1996), but this is not well established in those with schizophrenia.

The literature appears to suggest that those with severe forms of schizophrenia may smoke more frequently, and more heavily, than those with less severe forms (Lohr & Flynn, 1992). The possible beneficial effect of nicotine (and smoking) on schizophrenic symptoms and antipsychotic side-effects may be obscured by this association between smoking and severe forms of schizophrenia. In summary, a critical reading of the literature lends very limited support to the self-medication hypothesis, but this effect may be obscured by the association between severe forms of schizophrenia and heavy smoking.

Nicotine dependence and symptoms in schizophrenia