KCNH2 and polymorphic ventricular tachycardia: All these side effects will depend on dose, with high dose being determined as >100 mg daily.4 Another relatively unknown side effect is cardiotoxicity, as it has recently been associated with polymorphic ventricular tachycardia and QT prolongation, with subsequent TdP.5 Methadone inhibits the hERG, which is located on chromosome 7, and codes for the potassium ion channel which intercedes repolarization of the cardiac action potential.6,7 Methadone has also been associated with bradycardia due to its anticholinesterase effects, which can aggravate QT prolongation.