In pharmacology and toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%") is a measure of the lethal dose of a toxin, radiation, pathogen, or psychoactive substance. The value of LD50 for a substance is the dose required to kill half the members of a tested population after a specified test duration. LD50 figures are frequently used as a general indicator of a substance's acute toxicity. A lower LD50 is indicative of increased toxicity.
The choice of 50% lethality as a benchmark avoids the potential for ambiguity of making measurements in the extremes and reduces the amount of testing required. However, this also means that LD50 is not the lethal dose for all subjects; some may be killed by much less, while others survive doses far higher than the LD50. Measures such as "LD1" and "LD99" (dosage required to kill 1% or 99%, respectively, of the test population) are occasionally used for specific purposes.
Lethal dosage often varies depending on the method of administration; for instance, many substances are less toxic when administered orally than when intravenously administered. For this reason, LD50 figures are often qualified with the mode of administration, e.g., "LD50 i.v."
It should be noted that the tests usually determine LD50 on animals such as laboratory mice and such may have limited applications when applied to human use. As a measure of toxicity, LD50 is considered to be somewhat unreliable, and results may vary greatly between testing facilities due to factors such as the genetic characteristics of the sample population, animal species tested, environmental factors and route of administration.
- What is a [sic!] LD50 and LC50? | http://www.ccohs.ca/oshanswers/chemicals/ld50.html
- Tatken, R. L., & Lewis, R. J. (Eds.). (1983). Registry of Toxic Effects of Chemical Substances.
- Ernest Hodgson (2004). A Textbook of Modern Toxicology. Wiley-Interscience (3rd ed.)