Tardive dyskinesia (TD) is a movement disorder observed in a chronic neuroleptic treatment. Smoking is presumed to increase the prevalence of TD. the question of a cause-effect-relationship between smoking and TD, however, remains to be answered. Purpose of this study was to examine the correlation between the degree of smoking and the severity of TD with respect to differences caused by medication.

We examined 60 patients suffering from schizophrenia and TD. We compared a clozapine-treated group with a group treated with typical neuroleptics. Movement disorders were assessed using the Abnormal-Involuntary-Movement-Scale and the technical device Digital-Image-Processing providing rater independent information on perioral movements.

We found a strong correlation (.80< r< .90, always p< .0001) between degree of smoking and severity of TD. Repeated measurements revealed a positive correlation between changes in cigarette consumption and changes of the severity of TD (p< .0001). Analyses of covariance indicated a significant group-effect with a lower severity of TD in the clozapine-group compared to the typical-neuroleptics-group (p=.010). Interaction-analyses indicated a higher impact of smoking on the severity of TD in the typical-neuroleptics-group compared to the clozapine-group (p=.033) (Diehl et al., 2008).

Concerning a possible cause-effect-relationship between smoking and TD, smoking is more of a general health-hazard than neuroleptic exposure in terms of TD.