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There is a popular aphorism in Russia, translated as "one drop of nicotine kills a horse":

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, which is widely used on the anti-tobacco posters etc.

Can 0.05 ml of nicotine really kill a healthy 400-kg horse? What could be the origin of this phrase?

  • Depends on the concentration of nicotine... – nico Sep 14 '12 at 10:58
  • @nico: Wiki says it's "oily liquid". But let's make it 50 mg. – Quassnoi Sep 14 '12 at 11:09
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    LArge quantities of nicotine are very harmful. There is nearly enough in two packs of cigarettes to kill you if it was all taken at once. But, the nicotine receptors that provide pleasure from smoking self saturate, limiting the desire for more until the nicotine has been metabolised. And the body clears it moderately quickly. This almost eliminates the likelihood of nicotine poisoning from smoking unless you force yourself to smoke several packets very quickly (this has happened and people have died). – matt_black Sep 15 '12 at 13:29
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Toxicity: 30–60 mg (0.5–1.0 mg/kg) can be a lethal dosage for adult humans.

As a rough estimate, a horse can be 400kg, so a lethal does of 200mg-400mg for a horse. Density from wikipedia 1.01 g/cm³.

This means a lethal dose would take up 0.25-0.5 cm³ which is a drop of diameter 0.8-1 cm. This is quite a large drop, approximately 5-10times the dose you stated (0.05ml), but isn't too far from being a drop.

If horses are particularly susceptible to nicotine, then it could well be a lethal dose at 0.05ml.

Edit: This puts the LD50 (The dose where half the subjects die) in horses as 100-300 mg/animal, so if 2.5 0.05ml drops kill 50% of horses, its possible that 1 drop could kill a horse, even if it didn't kill most horses.

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    The LD50 for humans is not necessarily equivalent to the LD50 for horses. – Jordan Bentley Sep 14 '12 at 15:14
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    @JordanBentley is right - LD50 doesn't translate across species. But I think Nick's answer is as accurate as you could get without killing a number of horses. – Coomie Sep 17 '12 at 4:43
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    @Coomie but someone did kill a number of horses to get a more accurate answer science.sciencemag.org/content/127/3305/1054 , and the amount of nicotine required is really about 10 times more. – DavePhD May 26 '16 at 18:26
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    @DavePhD "Many horses died to bring us this information" - Mon Mothma – Coomie May 30 '16 at 1:18
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It takes more than a drop of nicotine, swallowed, to kill a horse.

This paper is about a number of mules that died from eating nicotine-contaminated feed. It claims, without a clear source, that:

The reported minimal lethal dose (MLD) of nicotine for the horse is 100-300 mg.

Tobacco has been used to de-worm horses, so it clearly isn't immediately toxic. It isn't recommended though.

Nicotine is an effective nerve poison - injecting it directly into the brain has far more severe effects, but that is hardly a useful warning against cigarette smoking.

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Pharmacology and Toxicology of Nicotine with Special Reference to Species Variation Science 02 May 1958: Vol. 127, pages 1054-1055 reports actual experimental data by injecting nicotine into the muscles of horses.

It was determined that the "minimal effective dose" (meaning minimal dose required to cause paralysis) was 4.0 mg/kg and the "approximate lethal dose" was 8.8 mg/kg.

So a 400 kg horse would require more than a gram to cause paralysis and 3 to 4 grams to cause death, which is much more than 1 drop.

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