The prescription drug methadone accounted for 2 percent of painkiller prescriptions in the United States in 2009, but was involved in more than 30 percent of prescription painkiller overdose deaths, according the Centers for Disease Control and Prevention. Prescription painkiller overdoses were responsible for more than 15,500 deaths in 2009.

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. According to the report, 4 of every 10 overdose deaths from a single prescription painkiller involved methadone, twice as many as any other prescription painkiller.

Methadone has been used safely and effectively for decades to treat drug addiction, but in recent years it has been increasingly used as a pain reliever. As methadone prescriptions for pain have increased, so have methadone-related nonmedical use and fatal overdoses. CDC researchers found that six times as many people died of methadone overdoses in 2009 compared to methadone-related deaths in 1999.

Read more from Centers for Disease Control and Prevention.