For reasons not totally understood, the mortality rate from unintended injury in the United States rose 11 percent between 1999 and 2005, a new study finds. The jumps in poisoning deaths and deaths from falls were particularly high and troubling, researchers said.

Overall, 89 percent of the total increase in unintentional injury deaths in the U.S. between 1999 and 2005 was due to poisoning among those 15 to 64 years old and falls among those 45 and older, which increased by about 11,200 and 6,600, respectively.

"While we don't know the cause behind the recent increase in falls mortality, it appears that the increase in poisonings is largely due to prescription drugs," said study co-author Susan P. Baker at Johns Hopkins University.

Other studies have also found alarming increased in prescription drug overdoses, while prescriptions for antidepressants, in particular, have soared. Meanwhile, overall abuse of certain prescription drugs nearly doubled from 2000 to 2007, according to separate research by the U.S. Department of Health and Human Services.

"I think part of it is a misunderstanding of what prescription means; it doesn't mean safe," Dr. Lewis Nelson of the NYU Langone Medical Center told LiveScience in a July interview. "It also at some level means a little more easy access to it. So you don't have to stand on the street corner and deal with shady characters." Nelson points out that this is particularly the case with teenagers, who are increasingly abusing such drugs.

Baker called for national prevention efforts to control the abuse of prescription drugs and limit access.

Oddly, the changes in death rates were significantly different by race and gender.

The death rate from falls increased 38 percent for white men and 48 percent for white women 65 and older. Yet it didn't change significantly for older blacks of either sex.

The study is detailed online at the website of the American Journal of Preventive Medicine and will be published in the September print edition of the journal. It was funded by the university.

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