From the drug interaction checker:
âMethadone may cause dose-related prolongation of the QT interval. Coadministration with other agents that can prolong the QT interval may result in elevated risk of ventricular arrhythmias, including ventricular tachycardia and torsade de pointes, because of additive arrhythmogenic potential related to their effects on cardiac conductionâ¦
â¦If taking drugs that also cause central nervous system and/or hypotensive effects (e.g., psychotropic drugs like
tricyclic antidepressants, phenothiazines, and neuroleptics), patients should be made aware of the possibility of additive effects with
methadone and counseled to avoid activities requiring mental alertness until they know how these agents affect them.â
http://www.drugs.com/xq/cfm/pageID_1...e/qx/index.htm