Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 14 3 2019 07 28 248 252 EN Effat Davoudi-Monfared Department of Clinical Pharmacy, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. Mojan Radmehr Department of Clinical Pharmacy, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. Padideh Ghaeli Roozbeh Psychiatric Hospital, Tehran University of Medical Sciences, Tehran, Iran. Maryam Mousavi Research Center for Rational Use of Drugs, Tehran University of Medical Sciences, Tehran, Iran AND Roozbeh Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2019 04 09 Valproate-induced hyperammonemia is a common side effect of valproate, which may occur either without any symptoms or may rarely cause symptoms of encephalopathy. Different risk factors have been defined for this side effect, including some nutritional deficiencies and polypharmacy (eg, other anticonvulsants). Three cases with psychiatric disorder who showed symptoms of severe hyperammonemia encephalopathy and had taken valproate with antipsychotics, especially risperidone, are presented here. In all cases, the symptoms were improved by discontinuation of valproate. Administration of antipsychotic may be considered as a risk factor for hyperammonemic encephalopathy related to valproate, specifically in some prone populations. https://ijps.tums.ac.ir/index.php/ijps/article/view/1728 https://ijps.tums.ac.ir/index.php/ijps/article/download/1728/883