Drug And Supplement Interactions
Chester J. Zelasko, Ph.D. | April 27, 2004

Recently the popular press reported on a study that examined the use of dietary supplements in patients who took prescribed medications (1). The study examined the use of dietary supplements in 458 outpatients who were taking at least one medication. Although the tone and tenor of the article and subsequent reporting was cautionary, the study revealed some interesting results.

Of all subjects in the study, 197 (43%) were taking at least one dietary supplement. Based on the way the data were reported, 76% of the subjects were taking a multivitamin-multimineral, but the researchers didn't report how many of those taking a dietary supplement were taking only a multivitamin-multimineral. That may have implications for all of us because multivitamins-multimineral supplements have been recommended for all adults in the United States (2).

Of all the different types of supplements subjects took, there were no recorded incidents or problems attributed to the interactions of the supplement with the medication--even in persons who took over six different dietary supplements a day. That doesn't mean the interactions didn't happen, but it would seem surprising that they wouldn't be noted in the patients' medical charts. Most of the interactions described were possible or probable interactions but not really based on actual research. The authors correctly point out that there is a lack of research on interactions between medications and dietary supplements.

This is not unique to dietary supplements. There is little to no research on the interactions of medications with most types of food, with the use of alcohol, or even something as simple as taking your medications in relation to when you exercise. Neither is there much research on the interaction of medications with other medications. Most warnings on interactions between medications began as the result of adverse effects reported to the U.S. Food and Drug Administration. Until negative effects are reported, it's doubtful that any manufacturer investigates whether an interaction is possible. In short, there is much research to be done on all forms of interactions between medications, foods, and dietary supplements.

The researchers concluded that while the potential for interaction is present when medications and dietary supplements are taken together, the potential for severe interactions is quite low (6%)--and none had actually been reported.

Where does that leave you? What should you do if you're taking a medication and dietary supplement at the same time? Most importantly, talk to your physicians. Keep them informed of the dietary supplements that you're taking on a regular basis--the name, the content if it's not obvious, and the amount. If they tell you to stop taking the dietary supplement because of a known interaction, you should do so. If they tell you to stop it without a known interaction being reported, ask why they recommend you stop. Remember, your physician is your partner in your healthcare and as such, should be willing to discuss, not simply dictate. There's another side to this story. The next time your physician tells you to quit smoking or lose weight or get some exercise, it's your responsibility to do that as well.


  1. Peng, CC, et al. 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.

  2. Fletcher, RH and Fairfield, KM. Vitamins for Chronic Disease Prevention in Adults: Clinical Applications. JAMA. 2002. 287:3127-3129.
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