A study found certain over-the-counter herbal medicines and dietary supplements taken concurrently with prescription drugs could have serious health risks, especially among older adults. Photo by Creative Commons

Sept. 25 (UPI) -- People who use certain over-the-counter herbal medicines and dietary supplements concurrently with prescription drugs could open themselves up to serious health risks, especially among older adults, according to a study.

Researchers in Britain found some drugs' effectiveness was reduced and that new medical problems could be caused with some combinations in a study published Monday in the British Journal of General Practice.


They report that blood pressure treatments, statins and aspirin are affected, and there is increased blood glucose concentration and risk of bleeding. They also found the body's reduced ability to absorb prescription drugs associated with aging.

Researchers found 32.6 percent of the participants were at risk of potential adverse drug interactions.

Substances with potential drug interaction risks include evening primrose oil, St. John's wort and ginkgo. Supplements include glucosamine and Omega3 fish oil.

"The potential risk of interactions with certain combinations of prescription drugs, herbal medicines and dietary supplements shows the need for healthcare professionals to routinely ask questions regarding the use of other medications that are not prescribed," Dr. Taofikat Agbabiaka, a researcher at the University of Hertfordshire in England, said in a press release. "This would help to initiate conversations about wider herbal and dietary supplement use and their possible interactions to help increase patient safety."

Twenty-eight of the 55 herb-drug and supplement-drug combinations were assessed as "no interaction" or "no interaction of clinical significance." But 21 combinations were categorized as interactions with "doubts about the outcome of concurrent use." Three combinations were rated as "potentially hazardous" and three of "significant hazard."

The significant ones were Bonecal supplement/Levothyroxine medicine, peppermint supplement/Lansoprazole and St. John's war supplement/Amlodipine.

The study was conducted in 2016 at two practices in South East England.

One third of the 149 participants said they used herbal medicines and dietary supplements bought over the counter and by self-prescription. The study also found that some patients were taking as many as eight types of alternative medicines and supplements.

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Seventy-eight percent of the concurrent users were taking dietary supplements, including vitamins and minerals.

The most commonly used dietary supplements were cod liver oil, glucosamine, multivitamins and vitamin D. Common herbal medicinal products were evening primrose oil, valerian and Nytol Herbal, which is a combination of hops, gentian and passion flower.

In a recent systematic review, also led by Taofikat, the concurrent use of prescription drugs with herbal remedies and dietary supplements was found to be substantial among older adults. These include common herb-drug combinations such as garlic-aspirin and ginseng-warfarin.

The U.S. Food and Drug Administration treats dietary supplements more like special foods and they are not put through the strict safety and effectiveness requirements of drugs. The FDA regulates dietary supplements under the Dietary Supplement Health and Education Act of 1994.

Dietary supplements cannot contain anything that may have "a significant or unreasonable risk of illness or injury" when the supplement is used as directed on the label, or with normal use if there are no directions on the label.