Findings from a cross-sectional survey of older adults revealed the most commonly used dietary supplements were cod liver oil, glucosamine, multivitamins, and vitamin D.
Out of the 155 responders, 20% used only herbal medicinal products (HMPs) with prescription drugs. Common HMPs were evening primrose oil, valerian, and Nytol Herbal (a combination of hops, gentian, and passion flower).
“This research has highlighted potential risk of interactions with certain combinations of prescription drugs, HMPs, and dietary supplements,” said the team, who were based at the University of Hertfordshire.
“If applied to the UK population that would mean 1.3 million older adults are at risk of at least one potential herb–drug or supplement–drug interaction.”
The use of herbal medicines and dietary supplements by older adults is common as are the rates of medication-related problems due to comorbidities and slower clearance of pharmacologically active compounds.
A recent systematic review established that concurrent use of prescription drugs and HMPs is substantial among older adults, with potential interactions from some herb–drug combinations such as garlic–aspirin and ginseng–warfarin.
However, the only available UK study on this issue among older adults is close to 15 years old, included people aged over 50 years, and relied on a self-selected sample from a publication’s readership.
Taking a sample group of older adults aged 65 years and above, who took one or more prescription drug, the research team posted out over 400 questionnaires receiving 155 returned forms.
The researchers found females were more likely than males to be concurrent users (43.4% versus 22.5% with the number of HMPs and dietary supplements ranging from 1 to 8, (mean = 3, median = 1).
The majority of concurrent users (78.0%) used dietary supplements with prescription drugs. In addition to the commonly used dietary supplements and common HMP, the team calculated that 16 participants (32.6%) were at risk of potential adverse drug interactions.
“A response rate of 39% is disappointing but high for a study of this kind and enough to provide credible findings,” the study said.
“Examples of HMPs and dietary supplements were included in the questionnaire. It is possible that some participants did not consider products such as garlic or ginger used for medicinal purposes as HMPs and did not report them.”
This research also highlighted the problem with recall and what patients thought were HMPs or supplements.
“Targeted questioning about use of any alternative medicine or supplements could initiate conversations about wider HMP use and possible interactions,” the team suggested.
Thoughts from Food Supplements Europe
Patrick Coppens, director of regulatory and scientific affairs at Food Supplements Europe added that while the study used a small sample of only two general practices, it was not surprising that 30% of people took food supplements while taking medicines.
“The inverse would probably also be true. Food supplements cover a wide range of food compounds that consumers chose to complement their diet with.
“The interactions described in the paper come from literature. The study does not establish that these interactions occurred in the sample investigated.
“Nevertheless, knowledge on interactions is important and is collected in relation to individual medicinal products. Such possible interactions are mentioned in the medicinal leaflet.”
Coppens added that the regulatory framework already provided for the requirements of the information in the medicinal product leaflet, which included information on interactions and contra-indications.
“The legal framework for food supplements also enables the legislator to require information being mentioned for certain food products, wherever necessary.
“Formation and awareness are important tools that can ensure that possible interactions can be prevented. This is however not something that can be considered as part of legislation.”
Source: British Journal of General Practice
Published online: doi.org/10.3399/bjgp18X699101
“Prevalence of drug–herb and drug–supplement interactions in older adults: a cross-sectional survey.”
Authors: Taofikat Agbabiaka, Neil Spencer, Sabina Khanom and Claire Goodman