Is there an example of substances interacting with each other in the following way?

  • A is a lethal substance, killing within minutes to hours when orally ingested;
  • anti-A is an antidote for A (or at least significantly counters its effect), works even if administered (orally) a few minutes after being exposed to A;
  • B is a lethal substance, killing within minutes to hours when orally ingested. Initially does not present with severe symptoms. However, administering anti-A after being exposed to B accelerates/exacerbates the effect of the latter, causing the death to occur virtually instantly.

Bonus points if A and anti-A are naturally occurring substances. As this is going to be a part of a D&D session, answers with A, anti-A and B belonging in either real life or the D&D universe are also welcome (if some of the required aspects are not canonically established, a brief medico-biological justification for why they might plausibly interact in this way is expected). If I can think of any other pertinent points, I will elaborate.

Edit: Thank you all for your suggestions! I settled for a minor development of Willk's answer: namely, replacing sarin with onchidal (https://en.wikipedia.org/wiki/Onchidal). The underlying biological mechanism should remain largely the same, as far as I can tell.

  • $\begingroup$ Why were you envisioning that the anti-A would be administered? Did you have some reason in mind that B-exposure could be conflated with A-exposure? $\endgroup$ – Shalvenay Dec 23 '19 at 0:19
  • $\begingroup$ The killer administers B to the future victim but informs another person that they poisoned the victim with A. The other person, knowing that A takes a while to kill, rushes to administer anti-A. The upshot would be that the party witnesses the other person administering a substance to the victim, only for the latter to die immediately after. However, I also want the apparent suspect to be able to point out that anti-A alone would not cause the death as observed. $\endgroup$ – A Y Mullion Dec 23 '19 at 5:52
  • $\begingroup$ I take it both A and B would have a delay in their effects, normally, so that the victim is asymptomatic when presented to the intervenor? $\endgroup$ – Shalvenay Dec 23 '19 at 17:01
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    $\begingroup$ That would be convenient. However, supposing the one who administers anti-A is in quite a hurry and aloof enough, I think that it should be sufficient for B not to have caused any immediately noticeable symptoms by the time anti-A is administered (which I tried to convey with the remark "Initially does not present with severe symptoms"). $\endgroup$ – A Y Mullion Dec 23 '19 at 17:11

There are many procholinergic nerve gases and insecticide. Sarin is one.


Like some other nerve agents that affect the neurotransmitter acetylcholine, sarin attacks the nervous system by interfering with the degradation of the neurotransmitter acetylcholine at neuromuscular junctions. Death will usually occur as a result of asphyxia due to the inability to control the muscles involved in breathing. Initial symptoms following exposure to sarin are a runny nose, tightness in the chest, and constriction of the pupils. Soon after, the person will have difficulty breathing and they will experience nausea and drooling. As they continue to lose control of bodily functions, they may vomit, defecate, and urinate.

A treatment for sarin poisoning is the anticholinergic drug atropine.


Atropine is a medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate and to decrease saliva production during surgery.[3] It is typically given intravenously or by injection into a muscle.[3] Eye drops are also available which are used to treat uveitis and early amblyopia.[4] The intravenous solution usually begins working within a minute and lasts half an hour to an hour.[2] Large doses may be required to treat some poisonings.[3] Common side effects include a dry mouth, large pupils, urinary retention, constipation, and a fast heart rate.[3]

Atropine can also cause hallucinations and visions. There are anticholinergic chemical agents, including some of the earliest described chemical agents. They act like atropine.


The civil use of this type of agents dates back to antiquity and includes the use of plants such as thorn apple (Datura stramonium)that contain various anticholinergic alkaloids... Hannibal's army in 184 BC used belladonna plants to induce disorientation in the enemy. During World War II, the US military investigated a wide range of possible non-lethal, psychobehavioral chemical incapacitating agents.... One of the anticholinergic compounds, 3-quinuclidinyl benzilate, was developed and weaponized in the 1960s as a new chemical agent for battlefield use as a psychochemical[64] and assigned the NATO code BZ...

So chemical agents have included both procholinergic and anticholinergic agents. If you took atropine (an anticholinergic) in anticipation of Sarin (procholinergic) exposure but you were instead hit by an anticholinergic agent, that agent would have synergy with atropine and you would get extra anticholinergic effect. Which might be tough on you. Or maybe you would have useful and educational visions.

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    $\begingroup$ In Chemical defense training, it is important to know "what" type of chemical agent is being used. Atropine is the antidote to nerve agents, but is ineffective against "blood", blistering or "choking" agents. Using the atropine without checking the detector to see what kind of agent you have been exposed to could result in death since atropine is a poison in of itself. If you were quick enough to be masked before inhaling any nerve agent, then injecting atropine without any symptoms of nerve agent poisoning will also kill you. $\endgroup$ – Thucydides Dec 22 '19 at 22:14

This is a bit of a stretch, as it it won't kill everyone very quickly, but is close to your criteria (natural substances, antiA fixes A but exacerbates B). If you're okay with some very broad strokes and yada-yada-just-believable-enough attitude toward it, then you might be able to sneak by with this.

Lethal Substance A: Arsenic poisoning

Really, any metal poisoning will do for our purposes, it's just that arsenic has been around and used for millennia. Arsenic is a naturally occurring metal. Long-term exposure can lead to serious health issues and complications. A large enough quantity in the short term can be used as a poison.

Copper would also work as a metal poisoning. Again, really any metal poisoning will do for this situation.

Antidote for Metal Poisoning: Penicillamine

Penicillamine is derived from penicillin, which has a long history - penicillin is naturally found in molds, and even ancient Egypt, Greece, and India have documented histories of using fungi for the treatment of certain conditions. Although whether or not they were using those from the penicillin family is unknown, the penicillium family of bacteria are naturally occurring. Fermentation processes go back to ancient Egypt, so someone with know-how in a D&D universe could certainly ferment certain fungi to get penicillamine.

Penicillamine is used in metal poisonings. It's not a fun medication to take. Vomiting, diarrhea, etc. But in an emergency situation, if someone was poisoned with large amounts of copper or arsenic, they might prefer this to death. It's not an "antidote" per-se, but it will indeed treat the metal poisoning.

Lethal Substance B: Wasp Venom

A single wasp sting is unlikely to kill you (unless you have a serious allergy), but just like metal poisoning - if someone were to extract enough into a consolidated substance, it would indeed kill you. Not that quickly, but probably painfully. For our purposes we'll focus on one aspect of wasp venom - it's interaction with kidneys.

Penicillamine <=> Wasp Interaction

There are no known cases of penicillamine interacting with wasp venom. I don't think anyone would dare try it. But penicillamine has a long list of bad drug interactions. It's not the thing you shove down your throat for kicks and giggles.

Note that penicillamine also has very toxic reactions to renal and liver diseases. In other words, if your kidneys aren't functioning well, penicillamine will have a drastically exacerbating effect on the harm to your kidneys, which could be fatal.

Because wasp venom, in enough of a quantity, will get into and cause damage to your kidneys (pretty quickly too), then penicillamine will have a drastically exacerbating effect on this. While penicillamine is making you puke and pee out metals, this dehydration and impact on your kidneys could probably knock you unconscious pretty quickly, and kill you shortly thereafter.

It's not the "instant" death you're looking for, and I don't foresee any scientific research being done into the interactions between wasp venom and penicillamine, but if you're okay with some broad strokes and yada-yada-ing over details, then maybe this will work for you.

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    $\begingroup$ I’m trying to imagine a scenario where a character could wind up with metal poisoning, a shed load of wasp stings and a stash of penicillamine... None of these scenarios even start well. $\endgroup$ – Joe Bloggs Dec 22 '19 at 22:33
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    $\begingroup$ @JoeBloggs Mutated wasps from hell with arsenic in venom and pencillamine producing fungi growing on their copper fur? $\endgroup$ – PTwr Dec 23 '19 at 11:18
  • $\begingroup$ Would alcohol not work for B? It's hard on your liver, but not that hard to do serious damage on it's own (in reasonable quantities). $\endgroup$ – MadCake - Reinstate Monica Dec 23 '19 at 21:36
  • $\begingroup$ @MadCake-ReinstateMonica If you had a lot of alcohol, then maybe. But death from alcohol poisoning is rare because you usually pass out before you get there. The interaction with penicillamine would be in the liver and/or kidneys which would certainly be severe. Again, we're talking a lot of alcohol. $\endgroup$ – cegfault Dec 24 '19 at 13:36
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    $\begingroup$ How about wood alcohol? Much less is required for it to be dangerous, but you can still have small enough amount to not be deadly on it's own. However from what I've read while the liver does the job of turning methanol into formaldehyde and then to formate, the formate itself does not specifically attack the liver so idk $\endgroup$ – MadCake - Reinstate Monica Dec 24 '19 at 13:48


Ethylene glycol (found mostly in antifreeze, but could be obtained other ways) is harmful or fatal when ingested in large quantities. Ethyl alcohol is an effective antidote to glycol poisoning. Of course alcohol is easily obtainable as liquor of any kind, or sufficiently large amounts of beer.

However, alcohol interacts badly with a lot of medications. Most of these drugs are not as available as you may like, but caffeine and penicillin are on the list, and they are naturally occurring.

Unfortunately, these interactions may not be as deadly as you described, unless both drugs are taken in large quantities.

[EDIT] I didn't see that the second substance needs to be a poison too. Upon further research, I see that aspirin(totally naturally occurring as tree bark) interacts poorly with alcohol, but is not life-threatening. Unless it is in stupid quantities, though, at which concentrations it is already poisonous due to the blood thinning effect it has. If you can figure out how to get huge quantities of tree bark in a character, then this may work.

  • $\begingroup$ How many items are legitimately on that list, though? A lot of medicines were listed as "do not take with alcohol" as a way to 'dry out' British and Irish sailors while they were off-duty. (Alcohol, of course, being a way to kill of bacteria, and keep water safe to drink while they were on-tour. Rum and Limes were key to long journeys!) $\endgroup$ – Chronocidal Dec 23 '19 at 9:01
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    $\begingroup$ @Chronocidal The list that the link points to is a legitimate medical site about modern drugs drawing on modern information from the US FDA and the pharmaceutical manufacturers PDR. To the best of my knowledge neither of these sources prints false medical information to placate the concerns of British and Irish naval discipline from a century ago. $\endgroup$ – RBarryYoung Dec 23 '19 at 17:53
  • $\begingroup$ If alcohol is consumed with any mushroom containing coprine (like the common ink cap) it will cause "disulfiram syndrome", one of the possible effects (in larger doses) is heart attack. Unfortunately, coprine isn't toxic except in the presence of alcohol. $\endgroup$ – gngdb Dec 23 '19 at 20:59
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    $\begingroup$ @RBarryYoung Except, the list includes penicillin, which is one of the drugs that doesn't have interactions with alcohol - and is the "false medical information to placate the concerns of British and Irish naval discipline from a century ago" in question. In fact, drill down to the "Penicillin interactions" page, and ethanol is suddenly "missing" - unlike metformin. Since we've caught it in one lie, how many others are on there? $\endgroup$ – Chronocidal Dec 23 '19 at 23:19
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    $\begingroup$ I was not aware that any of these were falsified, although it makes sense why now. Oh well. $\endgroup$ – Master of Potato Dec 23 '19 at 23:24

House, first season, episode 5 features two instances of this in a row:

When the antihistamines he gives her cause an asthma attack, House administers epinephrine, and she suffers a minor heart attack.

I seem to recall there were other instances of “Oh no, this drug we gave the patient has made them worse” but it's been so long since I watched the series that this is the only one that springs immediately to mind.


So we have the killer, the victim, and the helpful but misguided bystander.

One way this could work is if V shows some symptom, K declares it's due to the wrong cause, prompting HBM to give a treatment that's lethal under the circumstances.

I see a way this could work. K gives a lung toxin that causes airways to close down, either toxic or allergic. This would cause shortness of breath, chest pain and possibly elevated blood pressure. If V & HBM had no idea, K could declare V was having a heart attack, which could prompt HBM to give propranolol (a beta blocker which can also cause airways to close in an asthma attack, but is appropriate treatment for a heart attack.) V stops breathing and dies dramatically.

Figuring out what killed V would require a really good pathologist unless drug B caused obvious and extensive lung injury, like mustard gas or inhaled corrosives-eg acid or lye. You could invent other lung toxins. Something could be added to a cigarette or something else that was deliberately inhaled.

The reason this works is shortness of breath is not specific to heart vs. lungs, and neither is chest pain, but treatments are very different. Some chemotherapy drugs are lung toxic even if administered IV or orally.



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