Strengths:

• Well-documented efficacy in acute mania and maintenance therapy – less so for bipolar depression (OFC). 
• Potential antidepressant effect.
• Low EPS risk (compared with conventional antipsychotics, e.g. haloperidol).

Weaknesses:

• Causes weight gain.
• Associated with diabetes and hyperglycemia (class effect).
• Associated with hyperprolactemia (class effect). 
• Associated with somnolence and depression (side effect).

Key claims:

Efficacy:

• Reduced relapse rate: significantly reduces rates of manic and depressive relapse
• Increased time to relapse: significantly prolongs the time to relapse into a depressive or manic episode
• At least as effective as lithium: olanzapine is at least as effective as lithium in prolonging remission in bipolar disorder and more effective than lithium in preventing relapse into mania
• OFC in bipolar depression: OFC is more effective than placebo or olanzapine alone in the treatment of bipolar depression and rapid-cycling depression
• No treatment-emergent mania: no risk of treatment-emergent mania with olanzapine or OFC therapy in depressed bipolar patients
• Improvements in HR-QoL: olanzapine and OFC improve HR-QoL in depressed bipolar patients

Tolerability:

• Fewer drop-outs than lithium: more patients remain on olanzapine therapy compared with lithium in the maintenance of bipolar disorder
• No QTc prolongation: olanzapine is not associated with QTc prolongation
  

General/positioning: 

• Olanzapine has been prescribed to over 12.5 million people worldwide

GSK counterclaims:

• Olanzapine has never been studied as a maintenance treatment in patients who were initially depressed at study entry.
• Olanzapine has been shown to be no more effective than lithium in preventing depressive episodes.
• The effect size for olanzapine in the treatment of acute bipolar depression is modest and smaller than that of lamotrigine. 
• Both olanzapine and OFC caused significant weight gain after only 8 weeks of treatment. 
• Depression and somnolence are consistently among the most frequently side effects observed with olanzapine maintenance treatment.
• Weight gain has been a significant issue in olanzapine treatment observed in every clinical trial presented to date.

Guidelines