What are two non lethal substances that will combine to create a strong poison when ingested close together?

Hopefully my character would be able to drink one of the substances mixed in to a wine or whiskey that is shared out with a few people, but does not kill anyone (yet!). Soon afterwards the character goes upstairs and takes some form of pill, which should have the other half of the poison in it. The pill could have been switched out weeks in advance, without detection. This combination kills them - but as multiple people drank the wine, and they have been taking the pill for days without being poisoned, it is difficult to piece together how they have been killed.

Preferably the two ingredients would be naturally occuring as it is a low-tech world, and without taste to help avoid detection, but I know that's very unlikely so no worries if it has some taste/smell! I'm sure I can find a way to play it off!

I have thought of sulphur tablets with Isopropyl aminoethylmethyl phosphonite in the wine, which creates a VX (a strong nerve agent), however I'm having trouble thinking of a way of the character being able to get hold of Isopropyl aminoethylmethyl phosphonite with only fantasy technology... Am also unsure of the quantaties needed etc.

Another option is an overdose of a certain chemical, with one half being in the wine and the other in the pills, but again I'm unsure of quantity and what would work best.

Edit: sorry forgot to say, the context is a murder mystery story in a fantasy world.

Thank you all so much!

  • 4
    $\begingroup$ Diet coke and Mentos come to mind. Each one alone is safe, but mix both in high enough quantities and you might cause internal damage quite spectacularly. $\endgroup$ Apr 23, 2020 at 18:11
  • 1
    $\begingroup$ Do you want this to be deliberate or accidental? $\endgroup$
    – Halfthawed
    Apr 23, 2020 at 18:34
  • 1
    $\begingroup$ Have you done any research on your own? I bet my yearly salary that there is such a thing... $\endgroup$
    – L.Dutch
    Apr 23, 2020 at 19:02
  • 1
    $\begingroup$ @Halfthawed deliberate! $\endgroup$
    – Mais
    Apr 23, 2020 at 22:14
  • 1
    $\begingroup$ @Mais then the question wouldn't qualify for worldbuidling. $\endgroup$ Apr 24, 2020 at 13:40

5 Answers 5


Coprine is a mycotoxine, found in the mushroom Coprinopsis atramentaria, thus being obtainable in low tech setting, if you know what to look for. The substance is toxic when mixed with alcohol - how to make the unsuspecting victim drink enough alcohol in wine is left as an excercise for the reader...


Grapefruit juice and Codeine (etc)

There is a lovely long list of medication that should not be mixed with Grapefruit Juice.

One large subset of these are prodrugs, which are not active medication when consumed, but become active when digested. They are transformed by chemical reaction during digestion,

Grapefruit juice (and a number of other compounds) can substantially increase how much active medication is produced from the prodrug. Thus triggering an overdose.

A common example is Codeine. Codeine is a fairly common painkiller, hard to notice if you are taking it on its own. it functions via being converted into morphine in the liver. Grapefruit juice increases how much morphine is made.

So you dose someone up with a large (but sublethal) does of codiene (e.g. in the food). Then serve grapefruit juice with the meal. They get to die of an opiod overdose


Alcohol and Opiods

Alcohol can react badly with other drugs and be potentially lethal. In the modern world it is dangerous to take alcohol with Codeine painkillers. These are available without prescription.

Opiods can be derived from plants like the poppy. The Victorians are famous for their opium dens. So modern technology is not needed to concentrate the important chemicals.


Monoamine oxidase inhibitors (MAOI) and anything from the long list of substances they are known for their possibly lethal interactions. MAOI occur naturally and have nasty, potentially lethal interactions with a lot of other substances.

This is also a problem. If you put MAOI in the wine some guests may eat aged cheese and get the nasty symptom themselves. If you put it in the pill, the victim may experience the interactions on random days before the attack.


You can build up tolerances to some poisons over the long term. Famously, this has been used for poisoning since the Renaissance era (IIRC) , so you can drink from the same bottle as your victim and survive.

Now go for the reverse: everyone else has built up immunity (because they grew up in an area which has lots of the relevant poison in the local water) but your victim, who came from elswhere did not. Hence, one person dead, everyone else baffled as to what killed him.

  • 1
    $\begingroup$ The question specifically states that they want two individually safe substances that become poisonous when consumed together. This doesn't seem to address that. $\endgroup$
    – Dast
    Apr 24, 2020 at 14:49

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .