Olanzapine- and clozapine-induced stuttering. A case series.

Drug-induced stuttering has been described in association with several drugs, in particular antidepressants and low-potency neuroleptics. Here we describe a case series of stuttering induced by the atypical neuroleptics olanzapine and clozapine. Patients receiving neuroleptic treatment were carefully screened for stuttering as a possible side effect. We have studied all patients in the outpatient department (800 per year) as well as most inpatients (1300 per year) within 3 years. Seven cases of drug-induced stuttering were observed. Six patients suffered from stuttering in association with olanzapine treatment, and one received clozapine. Stuttering arose on average 2-21 days after initiation of treatment and ceased 2-5 days after discontinuation. Most patients suffered from additional diseases, such as brain pathology due to cortical atrophy or celiac disease, or received concomitant medication (i.e. intrathecal morphine pump). Our case series suggests that the atypical neuroleptic olanzapine can induce stuttering in the absence of a history of stuttering without accompanying akathisia or general decline of function. It appears that preexisting brain pathology or concomitant anti-depressant medication might predispose some patients to this side effect.