Hormesis: changing view of the dose-response, a personal account of the history and current status.

This paper provides a personal account of the history of the hormesis concept, and of the role of the dose response in toxicology and pharmacology. A careful evaluation of the toxicology and pharmacology literatures suggests that the biphasic dose response that characterizes hormesis may be much more widespread than is commonly recognized, and may come to rival our currently favored ideas about toxicological dose responses confined to the linear and threshold representations used in risk assessment. Although hormesis-like biphasic dose responses were already well-established in chemical and radiation toxicology by the early decades of the 20th century, they were all but expunged from mainstream toxicology in the 1930s. The reasons may be found in a complex set of unrelated problems of which difficulties in replication of low-dose stimulatory responses resulting from poor study designs, greater societal interest in high-dose effects, linking of the concept of hormesis to the practice of homeopathy, and perhaps most crucially a complete lack of strong leadership to advocate its acceptance in the right circles. I believe that if hormesis achieves widespread recognition as a valid and valuable interpretation of dose-response results, we would expect an increase in the breadth of evaluations of the dose-response relationship which could be of great value in hazard and risk assessment as well as in future approaches to drug development and/or chemotherapeutics.