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Median lethal dose (LD50)

The median lethal dose, or LD50 (originally abbreviated as DL50 for dosis letalis, 50%) is a test used in animal experiments. It was designed by the British pharmacologist J W Trevan in 1927.

LD50 is the dose of any substance tested required to kill half the number (50%) of test animals. The test shows how much of a substance must be taken before it becomes deadly. For example, a rat must be fed 50 mg of nicotine per kilo of bodyweight before it dies.

Various forms of LD50 test include feeding the substance by mouth, applying it on the skin, and injecting it into veins, muscle tissue or the body cavity.

Animal rights activists oppose LD50 animal testing because the death from poisoning is slow and painful. The LD50 test is also controversial among scientists because of doubts about the usefulness and reliability of the results it gives. Some types of LD50 test, especially oral, have been phased out or banned in the UK.




A chemical compound that forms 0.6-3.0 per cent of the dry weight of tobacco. Nicotine acts as a stimulant in mammals, and is one of the primary reasons for smoking addiction.