An important related issue is the influence of smoking, and its cessation, on the effects of the medications most of these patients rely upon for the control of their psychiatric symptoms. Although smoking has long been known to significantly alter the metabolism, and thus the effects, of most antipsychotics, the extent and clinical significance of these influences have rarely been assessed. It is unclear to what extent smoke cessation (as well as initiation) changes the side effect profiles of these medications, and whether such changes contribute towards the difficulties in patients' ability and/or willingness to stop smoking.