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Incidence and Severity of Potential Drug–Dietary Supplement Interactions

An Exploratory Study of 2 Outpatient Practices

Background To explore the incidence and severity of potential interactions between prescription medications and dietary supplements.

Methods A survey was conducted on dietary supplement use in 458 veteran outpatients currently taking prescription medications. Self-reported dietary supplement use was cross-referenced with each patient's prescription medication list, and potential interactions were identified from several tertiary sources and medical literature searches.

Results One hundred ninety-seven patients (43%) were currently taking at least 1 dietary supplement with prescription medication(s). The most common products included vitamins and minerals, garlic, Ginkgo biloba, saw palmetto, and ginseng. Among these, 89 (45%) had a potential for drug–dietary supplement interactions of any significance. Most of these interactions (n = 84 [94%]) were not serious based on limited available evidence, giving an incidence of 6% (5/89) of potentially severe interactions among patients taking interacting drugs and dietary supplements and 3% (5/197) among patients taking coincident dietary supplements and medications.

Conclusions Although the use of dietary supplements appears to be very common among patients who also take prescription medications, most potential drug–dietary supplement interactions found were not serious. However, literature support was sparse at best. Health care providers should continue to inquire about dietary supplement use and consider the potential for interactions, regardless of their severity.


Catherine C. Peng, PharmD, BCPS; Peter A. Glassman, MBBS, MSc; Lauren E. Trilli, PharmD; Jocelyn Hayes-Hunter, PharmD; Chester B. Good, MD, MPH. Incidence and Severity of Potential Drug–Dietary Supplement Interactions in Primary Care Patients: An Exploratory Study of 2 Outpatient Practices. Arch Intern Med.2004;164:630-636.

Key concepts: dietary supplements, multivitamins, drug interactions