Maximum Tolerated Dose

The maximum dose that an animal species can tolerate for a major portion of its lifetime without significant impairment or toxic effect other than carcinogenicity.

Loosely, the highest dose of a chemical that when administered to a group of test animals does not increase the death rate during a long-term study. The purpose of administering MTD is to determine whether long-term exposure to a chemical might lead to any adverse health effects in a population, when the level of exposure is not sufficient to cause premature mortality due to short-term toxic effects. The maximum dose is used, rather than a lower dose, to reduce the number of animals that need to be tested (and thus, the cost of animal testing), in order to detect an effect that occurs only rarely. This analysis is used in establishing chemical residue tolerances in foods.