As with other antipsychotics, caution is advised when prescribing risperidone with medicinal products known to prolong the QT interval, e. g., class Ia antiarrhythmics (e. g., quinidine, dysopiramide, procainamide), class III antiarrhythmics (e. g., amiodarone, sotalol), tricyclic antidepressants (i. e., amitriptyline), tetracyclic antidepressant (i. e., maprotiline), some antihistaminics, other antipsychotics, some antimalarials (i. e., chinice and mefloquine), and with medicines causing electrolyte imbalance (hypokalaemia, hypomagnesiaemia), bradycardia, or those which inhibit the hepatic metabolism of risperidone.
Enako, kor pri ostalih antipsihotikih, je potrebna previdnost pri predpisovanju zdravil, ki podaljšujejo QT interval npr. antiaritmiki skupine Ia (kinidin, dizopiramid, prokainamid) in antiaritmiki skupine III (amiodaron, sotalol), triciklični antidepresivi (amitriptilin), tetraciklični antidepresivi (maprotilin), nekateri antihistaminiki, drugi antipsihotiki, nekatera zdravila za zdravljenje malarije (kininu sorodne učinkovine in meflokin) in zdravila, ki povzročajo motnje v ravnovesju elektrolitov (hipokaliemija, hipomagneziemija), bradikardijo ali zdravili, ki zavirajo presnovo risperidona v jetrih.