Joseph Serna / Los Angeles Times

Fatal drug overdoses have increased for the 11th consecutive year in the United States, new data show.

According to a research letter from the National Center for Health Statistics, 38,329 people died of drug overdoses in the United States in 2010, an uptick from the previous year and the latest sign of a deadly trend involving prescription painkillers.

In 2010, 57 percent of overdoses, or about 22,000, involved known prescription drugs. Three-quarters of those involved painkillers like Oxycontin and Percocet while another 9,400 involved some unidentified drug cocktail.

More than 74 percent of all prescription drug deaths were accidental, statistics show. Only 17 percent of overdoses were suicides. The numbers show how drugs in the opioid family, such as Oxycontin, methadone and codeine, were often implicated in fatal drug cocktails.

An opioid was found in 77 percent of overdoses that involved benzodiazepine, a central nervous system depressant like Valium, Xanax or Ativan. The addictive narcotic was also involved in 65 percent of overdoses with antiepileptic or anti-Parkinsonian drugs; 57 percent of overdoses with antidepressants; and 56 percent of overdoses with anti-inflammatory and fever-reducing drugs.

The research letter, published earlier this week, buttresses a Los Angeles Times investigation last year that showed a surge in painkiller prescriptions in California and across the nation has had fatal consequences.

Fatal prescription drug overdoses over the last decade have outnumbered deaths from heroin and cocaine combined, the Times reported. In nearly half of all accidental prescription drug deaths in Southern California, the deceased had a prescription for at least one of the drugs involved in the overdose.

The research letter was published in the American Medical Association journal and was written by scientists from the Centers for Disease Control and Prevention.