WASHINGTON (Reuters) - Methadone use contributed to more than 30 percent of U.S. overdose deaths from prescription painkillers, even though it is rarely prescribed for that purpose, the Centers for Disease Control and Prevention (CDC) said on Tuesday.

Methadone was developed in Germany in 1937, and has been used by U.S. doctors since the 1960s to treat drug addiction. Its use for chronic pain relief has been on the rise since the mid-1990s, largely due to its relatively low cost, and the drug now accounts for about 2 percent of prescriptions in the country.

The CDC report analyzed national data from 1999 to 2010, which showed six times as many methadone-related deaths in 2009, compared with 1999 -- making it a leading killer in what the CDC has previously described as a prescription overdose epidemic. More frequently prescribed drugs include highly addictive ingredients such as oxycodone and codeine.

"Methadone used for heroin substitution treatment does not appear to be a major part of this problem," CDC director Dr. Thomas Frieden said in a statement. "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."

Methadone carries more risks than other painkillers because it can build up in the body, particularly when taken three times a day as often prescribed, and lead to dangerously slow breathing.

CDC said federal efforts are under way to warn healthcare providers about the risks, but they had not put a dent in the increase in methadone prescriptions. In many cases the medication was being dispensed by providers without specific training in pain management, they added.