CHICAGO (Reuters) — Older adults in the United States are popping prescription pills, over-the-counter drugs and dietary supplements in record numbers, and in combinations that could be deadly, US researchers said.

They said more than half of US adults aged 57 to 85 are using five or more prescription or non-prescription drugs, and one in 25 are taking them in combinations that could cause dangerous drug interactions.

"Older adults in the United States use medicine and they use a lot of it," said Dr. Stacy Tessler Lindau of the University of Chicago Medical Center in Illinois, whose study appears in the Journal of the American Medical Association.

"While medications are often beneficial, they are not always safe," she said in a telephone interview. She noted a recent report that estimated US adults over 65 make up more than 175,000 emergency department visits a year for adverse drug reactions, and commonly prescribed drugs accounted for a third of these visits. For the study, Lindau teamed up with Dima Qato, a pharmacist and researcher at the University of Chicago.

They used data from a national survey of adults aged 57 to 85 and interviews with nearly 3,000 people in their homes to get a read on the medications they used on a regular basis.

They analysed potential interactions among the top 20 prescription and over-the-counter drugs and the top 20 dietary supplements, and found that 68 percent of adults surveyed who took prescription drugs also used over-the-counter drugs or dietary supplements.