Skip to main content
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).
LD50 by progamer124 May 16, 2004
Urban Dictionary Merch
Your favorite words on things you can wear, drink from, read, or give to a friend.
The Urban Dictionary Store sells gifts you’ll have to explain.
Sometimes used to describe the percentage of a woman's brain that is missing. The root of this comes from the abbreviation LD50 or Lethal Dose required to kill half of a population. In this case the LD stands for Lacking Discernment. Depending on the amount of brain missing, the number 50 can be substituted with any percentage greater than 50. Can be used in casual bar conversations so that no attention is drawn by the woman of topic.
Hey Ben, that girl is definitely LD50. She's so fucking stupid that I've caught her cheating on me 3 separate times and she still denies it!
LD50 by Bojangles0928 January 18, 2010
Related Words
Mudvaynes first official record studio album released on august 22 2000 and a lethal chemical dosage. Chemical dosage definition: 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.
*in science class* teacher: “today we’re talking about lethal dose 50 or ld50. Me in my mind: brbr deng brbr deng brbr deng brbr deng dig! dig! dig! dig! dig! dig! Noooooo!!!!!!!!!!!!!
Ld50 by Nascarfan2007 April 15, 2023
More from Urban Dictionary

briefcake 

"Did you check out the briefcake in courtroom C?"
briefcake by Ben Frey April 6, 2006
Word of the Day on November 3, 2026
Brought to public attention by Bob Woodward and Carl Bernstein in the book on the fall of Richard Nixon, All The President’s Men, ratfucker was Nixon’s term for a political operative who sows chaos among opponents; an agent provocateur. It is thought to have originated among campus political rivalries at USC, and seems to have some usage in the US military.
Along with Nixon’s other ratfuckers, Roger Stone caused fights at otherwise peaceful Democratic Party protests to generate a false narrative that the Democrats were violent and dangerous.
Ratfucker by Ricky Ramjet November 2, 2017
Word of the Day on November 2, 2026

countrypolitan 

Term used to describe someone who is a mix of both rural (country) and urban (metropolitan) lifestyles/upbringings. He/she is typically equally comfortable in both settings and is able to seamlessly slip back and forth between the two, appreciating the characteristics of each.
That ol' gal of mine drives the 12 lane freeway during the week and a John Deere on the weekends. She likes opra and the Grand Ol' Opry. I love them countrypolitan women.
countrypolitan by MOChick November 7, 2006
Word of the Day on November 1, 2026

Witch Bath 

A bath consisting of a variety of slats, oils, soaps or any other added ingredients such as fruits, milks, herbs or any other spices for health or beautifying benifits.
She brought home alot of stuff and took it to the bathroom. She must be taking a witch bath.
Witch Bath by carnieboy30 October 26, 2020
Word of the Day on October 31, 2026
Load more