Researchers from the University of Coimbra, Portugal, conducted an online survey of 311 healthcare practitioners and discovered that 90.6% recognized the clinical relevance of herb–drug interactions (HDIs), yet knowledge around specific interactions was limited, and only 57.6% reported routinely asking patients about food supplements or herbal product use.
“The findings reinforce the need to promote applied training, improve access to reliable information sources, and support the systematic screening of the use of food supplements, herbal products, teas, infusions, and other natural products in clinical practice,” the authors wrote in the journal Nutrients.
They noted there was a significant lack of knowledge around the impacts of supplements’ quality defects.
“Contamination with microorganisms, mycotoxins, or pesticide residues, and the presence of potentially toxic elements may alter the exposure profile and complicate the causal attribution of adverse events,” the report said. “Adulteration with undeclared pharmacologically active substances may additionally generate unexpected drug–drug interactions.”
Discussing the growing importance of knowledge around herb-drug interactions, the authors noted a 2022 survey from Foods Supplements Europe indicated approximately 88% of respondents from the EU had used an supplement at least once in their lifetime.
Yet, a substantial proportion of users do not disclose their use to healthcare professionals (HPs), with non-disclosure rates reported to reach 40–70%, often because they are not asked, perceive the products as safe, or do not consider them clinically relevant.
This is important because certain compounds found in food supplements, particularly herbal extracts, may interfere with the way medicines are absorbed, processed or act in the body, potentially affecting their effectiveness or safety.
This is particularly pertinent in the context of an aging population, the authors said, where multi-morbidity tends to increase with age and often results in the concurrent use of multiple medications.
“When combined with food supplements, herbal products, or specific dietary patterns, this polypharmacy may further increase therapeutic complexity,” the report said. “Several compounds present in food supplements, particularly medicinal plant extracts, may interfere with cytochrome P450 enzymes, transporters such as P-glycoprotein, or pharmacodynamic mechanisms, thereby altering the efficacy or safety of medicines.”
The identification and prevention of potential HDIs depend largely on systematic clinical assessment, medication history-taking, and open communication with patients.
Knowledge discrepancies revealed
The current study collected data from physicians, pharmacists, nurses and nutritionists actively practicing in Portugal, in public, private, or mixed healthcare settings between November 2025 and March 2026.
The self-administered online questionnaire was disseminated through the digital platforms of professional associations, healthcare institutions, and professional networks.
After exclusion criteria were applied, the data from a total of 311 HPs was analyzed. Most participants (90.6%) recognized the clinical relevance of HDI and considered that interactions should be addressed in clinical practice.
However, routine enquiry was less consistent: 57.6% reported asking patients about the use of supplements, multivitamins, or herbal medicines, and 46.0% asked about herbal teas or infusions.
Fewer than half of respondents reported prior experience of suspected interactions, access to sources considered reliable, and previous use of specific resources for checking interactions.
Knowledge on specific interactions varied considerably, with the proportion of correct responses ranging from 21.8% to 72.5% when asked about different interactions. The highest-performing items concerned valerian and benzodiazepines, coffee and intestinal iron absorption, and dairy products and tetracyclines. Conversely, the lowest-performing items involved chamomile and hormonal therapies, papaya and antihypertensive medicines, green tea and bortezomib, and liquorice and antihypertensive medicines.
The findings were in-keeping with prior international and local literature.
The authors concluded the results point to the need to strengthen the coverage of interactions in the undergraduate and postgraduate training of HPs.
However, they noted limitations of the research included the fact it is a pilot, cross-sectional study based on a self-administered questionnaire, which limits causal inference.
They said future research should pursue more representative national studies and the evaluation of targeted educational interventions to strengthen the safe concomitant use of natural products and conventional medicines.
An additional consideration for future research concerns the quality and compositional reliability of supplements and herbal products, they said.
“Future work should examine whether HPs recognize product quality as an additional determinant of product safety and, where undeclared pharmacologically active substances are present, of interaction risk,” the authors wrote. “Such research could be complemented by continued analytical surveillance of product identity, composition, and chemical and microbiological purity.”
Source: Nutrients, https://doi.org/10.3390/nu18162600 “Knowledge, Attitudes, and Clinical Practices Regarding Food–Drug, Herb–Drug, and Supplement–Drug Interactions: A Pilot Cross-Sectional Study Among Healthcare Professionals in Portugal”. Authors: W. Silva et al.
