A biological, physiological or biochemical response to a drug at a low dose may be completely opposite to that response when a larger dose is administered. Also, a response to a single dose of an agent may shortly afterwards be completely reversed. These observations are as old as the use of medicinal preparations or alcoholic beverages. The term "pharmacological inversions" can be used to describe these phenomena. A subset of the dose-response relationship is that of "hormesis." This term, "hormesis," is often used to denote the beneficial response of an organism to a low dose of a physical or chemical agent and a detrimental response to a much larger dose. Many, but not all, of the pharmacological inversions can serve as prototypes of hormesis. Examples of the dose-time effect or the dose-response relationship (which may include the phenomenon of hormesis) can be found among these agents: alcoholic beverages, anesthetic gases, barbiturates, some tranquilizers, many vitamins, caffeine, nicotine, salicylates, enzyme inducers and some toxic metals.