Scientifically, the use of adverse event reports to assess the safety of dietary supplements should be very similar to how the safety of drug and other medical products are assessed, but the unique regulatory situation of dietary supplements provides some additional challenges. Beyond the limitations inherent in postmarketing surveillance systems, this unique regulatory environment renders the assessment of dietary supplement adverse event reports of greater complexity versus that performed on reports regarding drugs, biologics, or medical devices.
Because premarketing safety studies are not required for dietary supplements, standard drug premarketing data, such as clinical pharmacology studies, are not likely to be available. As a result, significant clinical information such as how the product is absorbed, metabolized, and excreted is generally not available, nor is the product evaluated for possible interactions with foods, drugs, biologics, or devices. The lack of such clinical information generally does not allow specific populations at possible increased risk for adverse effects (such as children, the elderly, or those with renal and/or hepatic dysfunction) to be identified in a systematic manner.
In further important distinction from medical products, there are no current FDA regulations establishing a baseline mandatory standard for dietary supplement manufacturing (CFSAN, 2001). As a result, the situation of multiple manufacturers of a specific dietary supplement can result in significant variation from product to product. An illustrative example is a study of the St. John’s wort products available in Germany, which detailed wide differences among the content of hypericin and hyperforin products, and notable interbatch variability in some of the products (Wurglics et al., 2001). Thus, unlike the situation with prescription drugs, in which there is standardized quality control of the innovator product and generic versions in manufacturing, adverse event reports on a particular dietary supplement may entail several different products that can vary significantly in dietary ingredient concentration, both among and within individual products.
FDA’s proposed rule to establish current good manufacturing practices for manufacturers, with respect to both the production and labeling of dietary supplements (FDA, 2003a), addresses some manufacturing issues, but not all aspects of product-to-product variability. According to FDA, this proposed rule “would, for the first time, establish standards to ensure that dietary supplements and dietary ingredients are not adulterated with contaminants or impurities, and are labeled to accurately to reflect the active ingredients and other ingredients in the product” (FDA, 2003b).
The challenge of underreporting adverse events was described above as a general challenge in using spontaneous adverse event reports. A factor particular to dietary supplements, however, is that, unlike drugs, biologics,