Olanzapine significantly lengths the time to relapse into either a depressive or manic episode in patients with bipolar disorder

Lilly’s claim that olanzapine has efficacy in maintenence therapy is based on one randomized, placebo-controlled trial in which the drug demonstrated efficacy in preventing relapse into both manic and depressive episodes. FDA approval of a maintenance extension of the indication of olanzapine for acute mania was based on this trial. An additional maintenance study of olanzapine versus lithium showed some areas of superiority of olanzapine over lithium, especially in prevention of a manic relapse.

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