I et 18 måneders co- terapi studie af maniske eller blandede episoder hos patienter stabiliseret med olanzapin samt en stemningsstabilisator (lithium eller valproat), viste langtids olanzapin co- terapi med lithium eller valproat sig ikke statistisk signifikant overlegen overfor lithium eller valproat alene i forsinkelse bipolære tilbagefald, defineret i overensstemmelse med det syndromiske (diagnostiske) kriterium.
54 In an 18-month co-therapy study in manic or mixed episode patients stabilised with olanzapine plus a mood stabiliser (lithium or valproate), long-term olanzapine co-therapy with lithium or valproate was not statistically significantly superior to lithium or valproate alone in delaying bipolar recurrence, defined according to syndromic (diagnostic) criteria.