More than one in five older Americans may be taking combinations of medications that put them at high risk for potentially harmful drug interactions, according to a new study published in the Journal of the American Medical Association.

Researchers found that about 22% of U.S. adults between 62 and 85 had a medication regimen associated with a high risk of a major drug interaction between 2021 and 2023.

The finding represents a slight improvement from earlier years. In 2015 and 2016, nearly 26% of seniors in the same age range were taking medication combinations that placed them at high risk for a potentially harmful interaction.

Despite the decline, researchers said the latest figure still represents a substantial medication-safety concern among older adults.

"These findings underscore the need for continuing efforts to improve medication safety among older adults," lead researcher Dima Mazen Qato, a senior fellow at the University of Southern California, said in a news release.

The study examined data from nearly 5,000 older adults collected during two separate waves of a national study on health and aging. Researchers compared medication use during 2015-2016 with data collected between 2021 and 2023 to examine changes in potentially dangerous combinations.

One factor contributing to the concern is polypharmacy, generally defined as taking five or more prescription medications at the same time. Researchers found that the percentage of seniors taking at least five prescription drugs increased from 31% in 2015-2016 to nearly 36% in 2021-2023.

The use of multiple dietary supplements also increased during the same period. The share of older adults taking five or more supplements rose from less than 13% to nearly 17%.

Taking multiple medications does not automatically mean a person will experience a harmful reaction, but the number of drugs being taken can increase the possibility that one medication will alter the effects of another. Certain combinations can increase the risk of serious side effects or make a medication less effective.

For example, the heartburn medication cimetidine, sold under the brand name Tagamet, can increase the effects of the blood thinner warfarin. That interaction can raise the risk of excessive bleeding, according to Harvard Medical School.

Researchers identified antidepressants, statins and blood thinners among the medications most commonly involved in combinations associated with major interaction risks.

Qato said medication-safety efforts should therefore focus on commonly prescribed combinations, particularly those involving antidepressants.

The researchers noted that the decline in the overall percentage of seniors at high risk for major drug interactions occurred even as the use of multiple prescription medications increased. That suggests changes in prescribing patterns may have reduced some interaction risks, although a sizable share of older adults remains exposed.

The findings highlight the importance of reviewing medication lists as older adults accumulate prescriptions from different doctors and potentially add over-the-counter drugs or supplements. Drug interactions can sometimes be missed when multiple medications are prescribed by different providers.

Researchers said continued efforts to reduce unnecessary medication use and identify potentially harmful combinations could help improve medication safety among older Americans.