Lethal Dose, 50%. Refers to the
dosage of a given drug required to kill 50% of a test population. The LD50 is usually measured in units of mass of drug per units of body mass; for example,
mg/
kg. This type of measurement is used to help ensure that the size of the specimen has no effect on the dosage measurement, as a large specimen can generally take a larger dose of a
toxin without fatal effects. The measure is often known colloquially as the "semilethal dose;" while it may not always be lethal to a given subject, it will be lethal around half the time.
The LD50 for nicotine in rats is around 50
mg/
kg, but it is only 3 mg/kg in mice. What's the LD50 for humans, you ask? Well, if you're willing to participate in the experiment to find out, go buy some cigarettes and
knock yourself out (literally).
