Concurrent use of loperamide with CYP3A4 inhibitors (e.g., itraconazole, grapefruit juice, omeprazole, tonic water and cimetidine) or CYP2C8 inhibitors (e.g., gemfibrozil) can increase its plasma levels as well, with recurrent ventricular tachycardia having been reported in a patient who was taking large recreational doses of both loperamide and the CYP3A4 inhibitor, famotidine [190]. This evidence concerns the gene CYP3A4 and ventricular tachycardia.