Most schizophrenic patients experience morbidity over the course of their illness, as the illness runs a chronic course and full remissions are infrequent. Therefore, defining treatment resistance among schizophrenia is problematic. Not all patients respond to antipsychotic medication treatment and an estimated 30-50% are considered resistant to treatment. Treatment resistance normally occurs along a continuum and most patients manifest varying degrees of resistance to antipsychotic medications. Essock and colleagues discovered that more than 60% of the patients in state hospitals met the criteria for clozapine therapy and, therefore, they may qualify for treatment resistance.