Possible induction of mania and hypomania by olanzapine or risperidone: A critical review of reported cases

Background: Risperidone and olanzapine are atypical antipsychotics that are now widely used in clinical practice. Method: A MEDLINE search (1966-1999) showed that, following the introduction of these agents in recent years, 26 cases of induced hypomanic and manic syndromes have been reported during standard olanzapine (N = 10) or risperidone (N = 16) treatment. Results: A critical analysis of these case reports reveals that the effects on mood were sometimes insufficiently documented and that in about half of them (N = 16) evidence is highly suggestive of a causative role of risperidone or olanzapine in the induction of (hypo)manic symptomatology. Conclusion: Despite limitations, the available literature confirms intriguing effects of these 2 antipsychotics on mood. The risk factors as well as the mechanisms of action underlying these effects remain to be clarified.