The name LD₅₀ is an abbreviation for "Lethal Dose, 50%" or median lethal dose. It is the amount of the substance required (usually per body weight) to kill 50% of the test population.

The test was created by J.W. Trevan in 1927^[1] but has been phased out.^[2] The U.S. Food and Drug Administration has begun to approve non-animal alternatives to LD50, in response to research cruelty concerns and the lack of validity/sensitivity of animal tests as they relate to humans.^[3][4]

Examples

• Oral LD₅₀ of grain alcohol: 10.6 g/kg in young rats, 7.06 g/kg in aged rats.^[5]
• Oral LD₅₀ of nicotine: 50 mg/kg in rats.^[6]
• Oral LD₅₀ of Table Salt: 3000 mg/kg in rats ^[7]
• LD₅₀ of Delta-9-tetrahydrocannabinol (THC)^[8] (active ingredient found in Cannabis): Fischer rat, oral 1,270 mg/kg
• LD₅₀ of smoked and inhaled Cannabis or Marijuana: Unknown. At present it is estimated that marijuana's therapeutic index is around 1:20,000 or 1:40,000 (the "1" in the prior estimate is based on an "effective dose" of the .9 grams contained in NIDA-supplied marijuana cigarettes, although the potency of Cannabis changes based on the genetics of the source plant)^[9] placing its LD50 around at least 18,000g.

• LD₅₀ of Batrachotoxin: estimated at 1 to 2 µg/kg in humans.
• LD₅₀ of Polonium 210: estimated at 10 (inhaled) to 50 (ingested) nanograms in humans makes this one of the most toxic substances known. One gram in theory could poison 100 million people of which 50 million would die.