The Georgia Bureau of Investigation on Tuesday announced that prescription drug overdose deaths declined by 9 percent in 2011, reversing an upward trend that had prevailed since 2008.

There were 512 prescription drug overdose deaths in 2011, compared to 560 in 2010. Total overdose deaths — those caused by prescription drugs, illicit drugs, or a combination of the two — also declined 9 percent from 729 to 664.

Middle-aged white people made up the largest majority of the deceased, and an overwhelming portion (91 percent) of the deaths were accidental. Eight percent were suicides and 1 percent were undetermined.

The anti-anxiety drug alprazolam (also known as Xanax), was the drug most commonly found in toxicology tests, contributing to 231 deaths in 2011. GBI Chief Medical Examiner Dr. Kris Sperry said that Xanax was more likely to be fatal when combined with other narcotics.

After Xanax, the next-worst offenders were the narcotic painkillers oxycodone (188), methadone (158) and hydrocodone (133). The only illicit drug on the top 10 list of drugs found in toxicology tests was cocaine, which caused 89 deaths last year.

The statistics were based on autopsies performed by the GBI medical examiner's office for 152 counties in Georgia. They did not include autopsies performed in Fulton, Cobb, Gwinnett, DeKalb, Henry, Hall or Rockdale counties, which have their own medical examiner's offices.