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I am writing a plot for a project I am working on, and I need to know if there is a poison that kills/incapacitates quickly (within 1 hour) when eaten, but has little effect upon injection. It needs to be toxic at less than 50 ml. I need it to be ineffective in the blood as part of an assassination plan.

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    $\begingroup$ This is a pretty good question. Most chemicals/plants/poisons work the other way around - they're deadly when injected but require higher doses or are ineffective if eaten. I won't be surprised if no one can offer an example of what you want, because it's counter-intuitive... but it'll be cool if one comes up. $\endgroup$
    – JBH
    May 19, 2021 at 23:32
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    $\begingroup$ OK, we could use some specifics. (a) What species are we talking about? (Never make assumptions on this site 😁) (b) What, exactly, do you mean by "quickly?" (days, hours, minutes, seconds, nanoseconds...) (c) How much of the consumable must be eaten? (d) Are you force-feeding or must it be hidden in some other food? (e) Are you looking for a specific answer (unlikely to exist), or will examples of ingestable-but-not-injectable be good enough for what you're trying to do? $\endgroup$
    – JBH
    May 19, 2021 at 23:42
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    $\begingroup$ And to give you an example for why I asked for those details: "Glycine in nuptial food gifts of decorated crickets decreases female sexual receptivity when ingested, but not when injected" explains how cricket sexual receptivity is reduced when a chemical is ingested - but not when it's injected. That could be used to create a suspension-of-disbelief solution to your problem. $\endgroup$
    – JBH
    May 19, 2021 at 23:49
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    $\begingroup$ To hazard a guess, it seems like it would almost have to be something that reacts with stomach acid (pH ≈ 2.5). Since blood is slightly alkaline (pH ≈ 7.4), something that is inert in that environment might work? BTW, when you say "injected", do you mean intravenous or intramuscular? Does it have to be liquid, or can it be something the size of an AVID chip? (In its current state, I won't be surprised if this gets closed for insufficient details.) $\endgroup$
    – Matthew
    May 20, 2021 at 1:39
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    $\begingroup$ If you are looking for something dangerous when eaten, why do you need an injection of it if people know it won't do anything. Wouldn't a poison like arsenic or plant-based poison like belladonna, which are both consumable, make more sense? I guess we just need more exposition. $\endgroup$
    – A Writer
    May 20, 2021 at 4:04

3 Answers 3

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I propose a more mechanical solution: nanocapsules. Take the poison of your choice, wrap tiny droplets of it in tiny hollow spheres, which should dissolve in stomach acid but not under white blood cell attack. At least not at the same rate: if the poison is released in a matter of minutes from stomach acid, but the blood takes days to do the same job, in the latter case the poison may be handled by the body at an acceptable rate and not kill the victim. It also helps if a few days is enough time for the poison itself to degrade and become inert.

I don't have any specific materials for you, partially because this science is relatively new, but there are a lot of proven and suggested mechanisms for the release of nanocapsule contents, including infrared light and ultrasound, so I do not think a chemical release mechanism is out of the question.

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  • $\begingroup$ I don't think you even need to quite that small but I agree with the concept. $\endgroup$ May 21, 2021 at 3:44
  • $\begingroup$ @LorenPechtel They need to be rather small to make injection into the bloodstream even possible. $\endgroup$
    – KeizerHarm
    May 21, 2021 at 9:26
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A substance that is non-poisonous when in a neutral form but became a poison on acidification might work. Such a substance could circulate in the neutral or slightly alkaline pH of the blood stream where it could be metabolized and removed from the body. But if ingested would change its form on contact with strongly acidic stomach acids leading to the formation of the poison.

I am not aware of any such substance, but I am fairly confident that such a thing could be synthesized. There are chemicals which undergo chemical changes across the pH range of interest such as Bromothymol blue. I don’t think this is particularly poisonous in either form but might well be chemically modified to be so.

There are a number of chelating agents used to absorb specific heavy metal poisons https://www.sciencedirect.com/topics/earth-and-planetary-sciences/chelating-agent With sufficient development is should be possible to develop a substance that would bind to a metal at blood pH and allow the chelated metal to be slowly filtered from the blood stream, but release the metal ion rapidly in the acidic conditions within the stomach.

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  • $\begingroup$ Metals are going to have a hard problem killing that fast. $\endgroup$ May 21, 2021 at 3:42
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There should be

I don't have a real life example ready, but there are as far as I know many molecules, not necessarily poison, that work that way. It's because of bindings. Let's look at it at a high over more or less correct way.

Some molecules are bound to others. This makes them act differently. This differently can be harmless, beneficial or bad. Look at sugers. They are often stored in long chains to each other like glucose. But this in itself doesn't help the body. They can only work when taken apart, freeing the bound energy when a free molecule is then paired with some enzymes. Another are things like ethanol. It isn't healthy in the blood, but it's the breaking down of the ethanol that produces the bad molecules. These are examples for things inside the blood, which is not what you want, but they are important as examples.

This idea is very important. Something directly into the bloodstream can be harmless, or at least not deadly/incapacitating. The processes there can possibly not unbimd or change these molecules, allowing you to piss or shit it out again. In contrast, via indigestion all kinds of special processes happen to break down and change the food. Acids, enzymes, bacteria and finally the passive/active diffusion into the blood, with first passage through the liver, can all change the molecules. Things that were bound can be freed, or some processes van result in new molecules with different effects, allowing it to roam free and start it's potentially harmful process. Imagine a solution of saltwater they use in hospitals bound to CO, Carbon Monooxide. In this fictional example, it might be harmless in the blood. It'll not react and get unbound. But if it passes through the digestion system, it could be broken down by a number of things. The CO is very good at diffusing into the blood, which we know from the lungs, which then can populate the red blood cells and basically suffocate someone.

So in short, you need something (relatively) harmless or even beneficial when directly put into the blood. But if eaten the processes can make something very lethal. I'm pretty sure someone can give real life examples.

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    $\begingroup$ Chelate's can be one of such classes of compound, but I guess there should be something more simple. As an example NaHCO not necessarly deadly in small quantaties in bloodstream, but in moderate quantaties ingested it can be a choke hasard because of foaming due the stomach acids $\endgroup$
    – MolbOrg
    May 20, 2021 at 11:47
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    $\begingroup$ Another vector to consider is a substance that a gut bacteria transforms into a poison. $\endgroup$
    – David R
    May 20, 2021 at 14:42
  • $\begingroup$ @DavidR man u are evil, lol. I think it will be a tricky one. Curious if there are some, and it turns out that there are viral agents for that, so yeah definetly possible. Potencial for such a nasty shtuff, worse than a nuke, hm, hope no one works on it ... This q/a has to be classified, for safety of humankind $\endgroup$
    – MolbOrg
    May 20, 2021 at 20:51

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