I'm looking for a poison A with the following characteristics:

  • A is a slow-acting poison (kills after 5-30 minutes)
  • A is hard to detect with normal human senses (can be infused in a drink like tea but can't be distinguished by a human without some equipment).
  • A acts as an antidote for another poison B. B just doesn't have to kill right away, no special characteristics.
  • A is a poison if consumed alone but acts as an antidote if consumed with B. The volunteer victim dies if only A or B is consumed, but survives if both A and B are consumed.
  • Both A and B can each kill in a regular pill's dosage. They don't need to be consumed in large amounts to kill. They must kill with around 100 grams or less.

What poisons A and B would meet those requirements? Asking for a friend...

  • 4
    $\begingroup$ The plausible deniability phrase on this website is 'asking for a novel', not 'asking for a friend'. $\endgroup$
    – Halfthawed
    Commented Dec 23, 2019 at 4:12
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    $\begingroup$ "Asking for a friend" just sounds funnier and sketchier, especially when asking about ways to kill someone. Also, this is for something I'm reading rather than writing. $\endgroup$ Commented Dec 23, 2019 at 4:38
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    $\begingroup$ IRL ethanol (alchol) and methanol are such a pair. Ethanol (alcohol) is a poison, but with quite a large dose (0,5-1l of pure ethanol). Methanol is a far more dangerous, but is easely cured with ethanol (if taken immediatly). But this is not an answer due to timeframe and doses $\endgroup$
    – ksbes
    Commented Dec 23, 2019 at 9:45
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    $\begingroup$ And, btw, 5-30 min - is a fast-acting poison. I would say very fast. "Normal" poison is from 6h to couple of days. Slow poision is weeks, months, years (mercury vapor, for example) $\endgroup$
    – ksbes
    Commented Dec 23, 2019 at 9:48
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    $\begingroup$ like ksbes said, 5-30m is very fast for a poison. A "slow-acting" poison would be several hours to days or even weeks. Also, anything that kills that quickly is very much unlikely to be safe, even if it's an antidote to something else. Anything that kills you so fast isn't going to have enough time to be neutralized by something else. $\endgroup$
    – cegfault
    Commented Dec 23, 2019 at 13:05

2 Answers 2


Consider, as an example, the use of atropine as a counteractant to organophosphate poisoning. Atropine, alone, is a reasonably poisonous substance - it is incapacitating at doses of 10 to 20 mg per person. Its LD50 is estimated to be 453 mg per person (by mouth).

Methyl parathion is an organophosphate classed as an extremely hazardous pesticide with a rodent LD50 of 6 to 24 mg/kg. It is an anticholinesterase compound. "Similar" compounds - I use the term loosely - are Sarin and Tabun, These are chemical warfare agents classified as nerve agents. Nerve agents are the most toxic and rapidly acting of the known chemical warfare agents. The LD50 of tabun was determined to be 240 micrograms/kg.

Overdose or poisoning with OPs causes hyperstimulation of nicotinic and muscarinic receptors - symptoms include :

blurred vision; tearing and sweating; loss of bowel and bladder control; difficulty breathing, as the airway may fill with fluid; tremors, muscle twitching, and seizures; coma and death.

Atropine acts an an antagonist to the OP - but dosage must be balanced against the real risk of atropine poisoning.


There is an uncited reference in the wikipedia page for Batrachotoxin (one of the toxins from frogs used in poison darts):

While it is not an antidote, the membrane depolarization can be prevented or reversed by either tetrodotoxin (from puffer fish), which is a noncompetitive inhibitor, or saxitoxin. These both have effects antagonistic to those of batrachotoxin on sodium flux.

Because this citation is needed, we should take this with a grain of salt. Accepting this on face value, however, both tetrodotoxin and saxitoxin are deadly themselves, but because the method of death is literally the opposite of batrachotoxin, then an perfectly measured dose might cause the two substances to neutralize / cancel each other out.


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