A Vital Signs report released by the Centers for Disease Control and Prevention in Atlanta said methadone was used safely and effectively for decades to treat drug addiction, but in recent years it has been increasingly used as a pain reliever.
The report found six times as many people died of methadone overdoses in 2009 compared to methadone-related deaths in 1999.
The researchers analyzed national data from 1999 to 2010, and 2009 data from 13 states part of a surveillance system for drug-related deaths.
"Methadone carries more risks than other painkillers because it tends to build up in the body and can disrupt a person's breathing or heart rhythm," the report said.
Four of every 10 overdose deaths from a single prescription painkiller involved methadone -- twice as many as any other prescription painkiller, the report said.
"Deaths from opioid overdose have increased four-fold in the past decade, and methadone now accounts for nearly a third of opioid-associated deaths," Dr. Thomas R. Frieden, director of the CDC, said in a statement. "Methadone used for heroin substitution treatment does not appear to be a major part of this problem. However, the amount of methadone prescribed to people in pain has increased dramatically. There are many safer alternatives to methadone for chronic non-cancer pain."