- Patients require treatment with drugs that are known to interact with clozapine (e.g., agents having a well-known potential to suppress bone-marrow functioning, drugs that are highly protein-bound, cimetidine, or phenytoin). Clozapine may also potentiate the effects of antihypertensives and anticholinergics; therefore, caution should be taken if patients receiving these drugs are enrolled in the study.