More and more Americans are turning to dietary supplements (vitamins, minerals, and herbal products) to treat a myriad of conditions and promote good health. Manufacturers of these supplements promote their products as natural, which leads many consumers to infer that they are safe. But natural does not necessarily mean safe. The lack of stringent regulation of dietary supplements by the government allows many potentially harmful supplements, such as ephedra, stay on the market for years before the FDA is able to ban them.

Because consumers tend to regard dietary supplements as harmless, many people don’t tell their physician that they are taking supplements—and most doctors don’t ask. But like drug-drug interactions, supplement-drug interactions can occur, and have the potential to adversely affect a person’s health.

But how common are supplement-drug interactions? A new study in the March 22, 2004 issue of the Archives of Internal Medicine found that 45% of veteran outpatients surveyed were taking supplements and drugs that could potentially interact. Only 6% of these interactions, however, were potentially severe.

About the Study

This study included 458 outpatients from two Veterans Affairs (VA) Medical Centers: one in Pittsburgh and one is Los Angeles. The participants were almost all older men (average ages 58-65). All of the participants were taking at least one prescription drug.

The researchers surveyed a sample of patients waiting for general medical appointments. The surveys asked the participants whether they were currently using or had ever used dietary supplements and, if so, whether they had informed their primary care provider that they were taking supplements.

From a variety of sources, the researchers identified potential supplement-drug interactions that had been documented or were theoretically possible. Interactions were classified as either:

  • Severe (if they had the potential to require emergency care or hospitalization, or lead to a life threatening event or permanent disability)
  • Not severe (if they caused little to no risk to a patient’s health)

The researchers cross-referenced the participants’ reported supplement use with records of their oral drug prescriptions. They used these data to identify participants who were taking supplements and drugs with the potential to interact.

The Findings

Forty-three percent (197) of the participants were currently taking at least one dietary supplement, and 18% (82) had taken supplements in the past.

Among the participants who were taking supplements, 46% (91) had potential supplement-drug interactions. However, only 6% (5) of these interactions were classified as potentially severe. Most of the potential interactions involved ginseng , garlic , Ginkgo biloba , and coenzyme Q .

Seventy percent (79) of the of the Pittsburgh supplement-users and 40% (39) of the Los Angeles supplement-users had informed their primary care providers that they were using dietary supplements.

These findings are intriguing, but they have three major limitations:

  • The survey consisted of veteran outpatients, so these findings may not be applicable to the general population.
  • Participants in Pittsburgh took the survey interview-style with an administrator, while participants in Los Angeles filled out the surveys themselves. This discrepancy may have affected the study findings.
  • This study evaluated only potential interactions, but did not follow the participants to find out if the interactions actually occurred. More extensive followup would have produced more accurate results.

How Does This Affect You?

These findings suggest that the incidence of severe supplement-drug interactions may be rare. While this is good news, it’s important to remember that the currently available evidence on supplement-drug interactions is limited. Unidentified interactions may exist and some populations (i.e., older adults or children) may be more susceptible to adverse effects of interactions than others.

This study highlights the need for more research on the risks and benefits associated with dietary supplements. Certain dietary supplements are beneficial for certain people, but the lack of research on most dietary supplements makes it difficult to offer conclusive or reliable recommendations.

Until more research is available, it’s important to avoid potential supplement-drug interactions. If you are taking a dietary supplement, make sure your doctor knows exactly which supplements you are taking. In the event your doctor prescribes a medication that could potentially interact with a supplement you are taking, he or she can work with you to change the supplement, discontinue it altogether, or closely monitor its potential for adverse effects, if the risk turns out to be low.