A patient on a stable dose of clozapine and a longstanding heavy smoker (20 cigarettes a day) is admitted informally to a smoke-free inpatient unit and stops smoking abruptly, using no nicotine replacement. Over the following one to two weeks, with no change in his clozapine dose, he becomes increasingly sedated with worsening hypersalivation and sialorrhoea. Which change in clozapine handling best accounts for this?
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