Toxicology

Toxicology is the study of the symptoms, mechanisms, treatments and
detection of biological poisoning, especially the poisoning of people.

Many substances regarded as poisons are toxic only indirectly. An example is
"wood alchohol" or methanol, which is not poisonous itself, but is
chemically converted to toxic formaldehyde in the liver. Many drug molecules
are made toxic in the liver, and the genetic variability of certain liver
enzymes makes the toxicity of many compounds differ between one individual
and the next. Because demands placed on one liver enzyme can induce activity
in another, many molecules become toxic only in combination with others. A
family of activities that engages many toxicologists includes identifying
which liver enzymes convert a molecule into a poison, what are the toxic
products of the conversion and under what conditions and in which
individuals this conversion takes place.

The term LD50 refers to the dose of a toxic substance that kills 50 percent
of a test population (typically rats or other surrogates when the test
concerns human toxicity).