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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 but has been phased out. 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. 
- Oral LD50 of grain alcohol: 10.6 g/kg in young rats, 7.06 g/kg in aged rats.
- Oral LD50 of nicotine: 50 mg/kg in rats.
- Oral LD50 of Table Salt: 3000 mg/kg in rats 
- LD50 of Delta-9-tetrahydrocannabinol (THC) (active ingredient found in Cannabis): Fischer rat, oral 1,270 mg/kg 1.270
- LD50 of smoked and inhaled Cannabis or Marijuana: unknown, at present it is estimated that marijuana's LD-50 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)
- 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.
- What is an LD50 and LC50
- LD50 test ban welcomed
- "Allergan Receives FDA Approval for First-of-Its-Kind, Fully in vitro, Cell-Based Assay for BOTOX® and BOTOX® Cosmetic (onabotulinumtoxinA)". Source: Allergan, Inc. News Provided by Acquire Media. Page last updated 24 June 2011. http://agn.client.shareholder.com/releasedetail.cfm?ReleaseID=587234. Retrieved 2011-06-26.
- "In U.S., Few Alternatives To Testing On Animals". Washington Post. Page last updated 12 April 2008. http://www.washingtonpost.com/wp-dyn/content/article/2008/04/11/AR2008041103733.html. Retrieved 2011-06-26.
- Alcohol Chemistry
- Safety (MSDS) data for nicotine
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- Inhalation, parenteral and oral LD50 values of Δ9-tetrahydrocannabinol in Fischer rats
- What is the lethal dose of marijuana?