Doctors should inform patients of arrhythmia risk when they prescribe methadone. They should ask patients undergoing or considering methadone treatment about any history of heart disease, arrhythmia, and fainting spells. Doctors should check the QTc interval on the patient's ECG before starting methadone treatment, within 30 days after starting treatment, and annually thereafter. If the QTc interval is greater than 450 ms but less than 500 ms, the panel recommends discussing benefits and risks of methadone with the patient and frequent monitoring. If the QTc interval exceeds 500 ms, the panel recommends discontinuing methadone treatment or reducing the methadone dose, eliminating possible contributing factors, or using an alternative therapy. Finally, doctors should be aware of interactions between methadone and other drugs that prolong the QT interval or slow the metabolism of methadone.