Information about human use of dietary supplement ingredients may be in the form of formal studies, such as clinical studies or trials and epidemiological studies; in the form of spontaneously reported adverse event reports and literature case reports; or in the form of information about historical use of the ingredient. Because dietary supplements are not required to undergo formal studies before marketing, formal study data available on dietary supplements are less commonly available than adverse event reports or information about historical use.

The different types of data about human use can be useful either as (1) an indicator of possible risk or (2) a mitigator of concerns raised by other data. For example, spontaneous reports are generally used to detect concerns, and historical use information is often presented as a mitigator of concern. Formal studies are less likely to be available, but if they are, they can be the source of information about adverse events in individuals, or they can be used to demonstrate an overall increase in risk of a particular adverse event associated with ingestion of an ingredient. Formal studies can also be used as mitigators of concern if they are adequately designed and powered to detect adverse events.

Within each type of human data, questions can be asked about the nature and quality of the scientific information to determine whether the information raises the level of concern regarding the probability to cause harm. In the sections that follow, the nature of evidence that increases concern is described and illustrated in a spectrum of concern figure. Information that independently raises a higher level of concern requires immediate attention to evaluate the potential of the ingredient to cause harm. For observations categorized as lower to moderate concern based on their placement on the spectrum, it is important to consider whether other types of human, animal, in vitro, or related data, as well as information about potential interactions (see Chapter 8), add to the level of concern. For many dietary supplement ingredients, human data regarding their safety or risk will not be available. A lack of data should not be interpreted as an absence of risk. Other types of data must be examined and weighed appropriately to understand the risk.

Adverse events associated with product use—whether reported directly to the Food and Drug Administration (FDA), manufacturers, distributors,