The US Food and Drug Administration (FDA) has issued an alert about reports of death and respiratory depression, cardiac arrhythmias, and other life-threatening adverse events in patients receiving methadone for chronic pain (http://www.fda.gov/cder/drug/infopage/methadone/default.htm).
Fatalities have been reported in patients who were switched from chronic, high-dose treatment with other opioids to methadone and in patients initiating treatment with methadone. The reported deaths and adverse events are the possible result of unintentional methadone overdoses, drug interactions, and methadone's cardiac toxic effects, the agency stated.
Hampton T. Methadone Alert. JAMA. 2007;297(4):354. doi:10.1001/jama.297.4.354-a