Adverse Effects and Laboratory Parameters of High-Dose Olanzapine vs. Clozapine in Treatment-Resistant Schizophrenia

Deanna L. Kelly, Robert R. Conley, Charles M. Richardson, Carol A. Tamminga, William T. Carpenter

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Patients with treatment-resistant schizophrenia pose a major challenge to caregivers since only clozapine is documented as having superior efficacy in this population. Although olanzapine is similar to clozapine in structure and receptor profile, it has not been proven to have superior efficacy for this patient group. Nonetheless, olanzapine is being increasingly used in higher doses as clinicians attempt to find a more effective and tolerable therapy for refractory patients. Furthermore, there are little data comparing olanzapine and clozapine in this population. Thirteen patients participated in a randomized double-blind 16-week crossover study of clozapine therapy (450 mg/day) compared to high doses of olanzapine (50 mg/day). No patients on olanzapine responded while 20% responded to clozapine treatment. Olanzapine patients tended to experience higher rates of anticholinergic effects such as dry mouth (80 vs. 20%) and blurry vision (40 vs. 0%). Clozapine-treated patients had higher rates of sialorrhea (80 vs. 10%), sweating (50 vs. 10%), dyspepsia (70 vs. 30%), and lethargy (90 vs. 60%). Neither treatment was associated with significant akathisia. Liver enzyme elevation and lipids were higher with clozapine treatment. Mean weight gain in the initial 8 weeks was 3. 4 kg for olanzapine and 1.2 kg for clozapine. High doses of olanzapine during 8 weeks of treatment did not increase lipids and liver enzymes like clozapine did. Olanzapine at 50 mg/day may be associated with more anticholinergic effects and weight gain than clozapine.

Original languageEnglish (US)
Pages (from-to)181-186
Number of pages6
JournalAnnals of Clinical Psychiatry
Issue number3-4
StatePublished - Sep 2003


  • Clozapine
  • Olanzapine
  • Schizophrenia
  • Side effects
  • Treatment-resistant

ASJC Scopus subject areas

  • Psychiatry and Mental health


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