gested, if a different plant part is now used, if the ingredient is formulated or processed differently, or if a different population is using the substance, then the level of concern should be raised. It is clear from these questions that historical use of a substance, even widespread historical use without documented ill effects, is no guarantor of long-term safety.

Historical use information is very useful when it describes a relationship between untoward effects and an ingested substance, as illustrated in Table 4-3. It is less useful in predicting safe use, especially if there are other reasons to be concerned about the possibility of effects that do not occur immediately following exposure. However, in the absence of other data that raise concerns about the safety of the substance, information about safe historical use may provide indirect evidence for lack of serious acute harmful effects if its relevance to current use conditions is carefully considered.

Information about the historical use of an ingredient may be most useful if it suggests potential adverse effects that could be anticipated. It is also helpful to compare relevant historical use information with other types of information that suggest possible harm (e.g., in vitro data, animal data, other human data, or data about related substances). While the historical use information should not be considered as more important than the scientific evidence, it may be appropriate to take information about the history of use into account if years of previous use would be expected to uncover the adverse effect under consideration. In such cases, historical use information may mitigate concerns to some degree.

Clinical studies evaluate the efficacy and/or safety of health care interventions in humans. There are several types of clinical studies, which differ