The use of poisons (often assumed to be in liquid form) on knives and other melee weapons, often by stealthy or roguish characters, is a classical fantasy trope. However, some have said it to be of questionable practicality due to the weapon not staying in the wound long enough to deliver a lethal dose of poison, or due to the poison not residing on the weapon long enough to reach its target.

Given the ability to design a knife and sheath specifically for this task, and a liquid neurotoxin that can be thickened by ordinary means, how would such a knife/sheath pair be designed to allow the blade to deliver a lethal dose of poison without having to manually coat the blade in the poison (messy, hazardous, and time-consuming) before each use? Would such a weapon be restricted in its usage (such as only being useful as a stabbing weapon, or requiring that the wielder leave the weapon in the victim)? How potent would the poison have to be in order to make this feasible?

For context's sake, this would be used in a stealth situation (such as an assassination), not in open combat...

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    $\begingroup$ A quick and short answer would be no, unless said weapon is used by a ninja/assassin, where you only want to gently tap the target and leave quickly. In that context, that may be a great way to use such a poisoned melee weapon. Although ranged poisoned weapons are far more practical and common. Take the medieval longbow for example. Archers would stick their arrows in the ground so that their arrow wounds would cause infections. Another scenario for real life poisoned ranged weapons was the chinese repeating crossbow that had barely any power, but was poisoned so only a scratch was enough. $\endgroup$ – grimmsdottir Feb 8 '15 at 23:02
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    $\begingroup$ @grimmsdottir: they'd stick weapons in worse than the ground to cause infection. $\endgroup$ – Steve Jessop Feb 9 '15 at 1:03
  • $\begingroup$ @grimmsdottir -- that is the context it appears in much of the time $\endgroup$ – Shalvenay Feb 9 '15 at 1:27
  • $\begingroup$ @SteveJessop well, neither of us quite want to say what they put their weapon in right? This is a fairly polite place $\endgroup$ – grimmsdottir Feb 9 '15 at 3:56
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    $\begingroup$ @DoubleDouble at least I see it as a problem! $\endgroup$ – RedSonja Feb 10 '15 at 8:37

10 Answers 10


As in many engineering problems, we can start by looking at how nature does it. In general, we see three common methods by which animals (and plants) poison one another. Contact poisons, injected poisons, and poisonous objects which are left in the targt.

Contact poisons

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This lovely little strawberry-looking dude is a poison dart frog. His method of poisoning is simple: touch him and die. This is true even for humans, though something like gloves would make it safe for a person to handle him.

Weapons could be coated with such a contact poison fairly easily. With something toxic enough that touching it would be lethal, slashing or stabbing someone would be lethal as well. The downside is that you have to be incredibly careful with contact poisons. Brush up against your sword? Dead. Get a little on your finger while coating your blade? Dead. Only a very cautious expert would want to use the sorts of poisons that will kill with a touch.

Injected poisons

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Many animals, rather than just letting a poison seep in through the skin, actively seek to inject poison into their victim. This has the advantage of getting the poison (or rather, the venom) right into the blood stream. This is common in predators, such as snakes and spiders, and is also used defensively by nudibranchs, though they cheat and steal the poison injectors off of jellyfish tentacles instead of making their own.

Injected venom isn't as lethal as contact poison, so it would be more manageable for a soldier to handle without killing himself. The difficulty is that it needs to be introduced into the victim's blood stream. Luckily, swords and spears are purpose-made for introducing themselves into a hapless victim's blood stream, so coating a weapon and slashing might still do the trick.

It also might be possible to develop a weapon that can do a better job of injecting its venom. You could, for example, create a spear with a hollow tip filled with pressurized venom. If the tip of the spear was a spring loaded valve that would get pushed in upon contact with the target, it could effectively pump a load of venom into any wound it made. The downside would be that all of this hollowing out of the spear head would make it more brittle, and the valved design probably wouldn't fare as well against armor. It would also need to be refilled and repressurized regularly, as the contents of its venom chamber would likely be spent after a blow or two.

Detachable Stingers

enter image description here

That's a bee stinger, plus the tip of its abdomen containing a venom sac and some muscle to keep it pumping once the barbs on the stinger lock it into its target. Some plants use this technique as well, leaving thin hairs filled with venom in your skin when you brush up against them. Some sea urchins have similar barbed, venomous spines that break off and burrow into the skin of unlucky divers that brush up against them.

The advantage of something like this is that, once your stinger embeds itself in the target, it will keep pumping more venom into them. The venom, like our injectable venom, need not be as nasty as contact venom. For something like a melee weapon, your best bet for going down this route would probably be a spear with a detachable spear head. The spear head could either be filled with venom, or else just made of something poisonous. If it were barbed and not attached too firmly to the shaft, it could be stuck into the target and would remain when the shaft of the spear was removed.

This approach would inject more venom, without the need for a system of rapidly pumping the venom into the target. It would also leave a big hunk of metal lodged in the skin of whoever it was used on, which would further add to the plight of that unfortunate soul.

The downside is that your spear no longer has a tip. I'd recommend making a second, general purpose stabbing tip on your spear and lashing the venomous tip on top of that one if you're going to use this approach. Of course, that will add weight, so either way your spear won't be as effective as a normal one.

Why poison still might not be worth it

Ultimately, there is still one problem with poison, regardless of what kind you use and how you inject it into your target: it doesn't act particularly quickly. A fast acting incredibly deadly toxin, like that found in poison dart frogs, still takes tens of minutes to kill its victim. Other poisons could take even longer. Hunters and snakes that use poisons to catch their food generally rely on poisoning the target and then following it around until it dies.

In close combat, tens of minutes is still enough time for the person that you just poisoned to kill you, and there usually isn't a place to run off to while you wait for your poison to do its job if you're using poison in the heat of battle. The best use of it would be in an assassination attempt, where the assassin intends to stab the victim and run off, but in that case, why bother with close combat? All of the same sorts of methods could be used with a longbow or a dart gun, in which case the recipient of the poison and their friends would never even need to see your face.

  • $\begingroup$ Your spear design seem like it would blow it's load all on one person. This may sound like a good idea, for one on one dueling, but you are highly unlikely to be carrying a spear, much less a poisoned one for dueling. That means that you would carry that spear to war, and what use is a spear that only works once, unless you have a backup spear, but even then, it is just not cost efficient. $\endgroup$ – grimmsdottir Feb 8 '15 at 23:03
  • $\begingroup$ If you're curious, I think the bird in that comic is the hooded pitohui. Touching it can apparently make your hands tingle and go numb. en.wikipedia.org/wiki/Hooded_pitohui $\endgroup$ – ckersch Feb 8 '15 at 23:08
  • $\begingroup$ @ckersch, I recall reading that Batrachotoxin resulted in very fast paralysis, even if it took 1/2 hour to kill. From an assassin's perspective, instant paralysis followed by death is good enough. Do you have a different view? $\endgroup$ – Serban Tanasa Feb 9 '15 at 0:06
  • $\begingroup$ Another argument against poison could be deterrence. The goal of a battle is not to kill as many of your enemy as possible, but to defeat them and demand a favorable peace treaty. To make opposing soldiers die of a horrible death after the battle could damage your reputation. If your unit is known for using poison in battle and you are captured, you might well be tortured and executed because of it, otherwise you might be held as a POW to be ransomed, exchanged, or released later. It happened reportedly with flamethrower troops in the World War, they were often executed on the spot if captured $\endgroup$ – vsz Feb 9 '15 at 7:11
  • $\begingroup$ @SerbanTanasa I haven't found any good sources that describe the paralysis time of batrachotoxin. One source said 'paralysis within minutes,' but was taking about hunting animals, so I'm not sure how long it would take on a human. I does look like the cause of death is paralysis of the heart, though, so I'm guessing that paralysis and death happen at around the same time. (Source: jrscience.wcp.miamioh.edu/fieldcourses06/…) $\endgroup$ – ckersch Feb 9 '15 at 14:59

Option 1: Specially Treated Blade Coated in, say, Batrachotoxin

This one's pretty nasty. Nerve paralysis is almost instantaneous, so no return stab from the victim if done right. The lethal dose of this alkaloid in humans is supposedly to be 1 to 2 µg/kg, which is about 2 grains of salt-worth, so even a thin coating on the tip of the blade should do just fine.

Option 2: Lead poisoning

Lead is toxic to the human body. Lead is also soft and blunt, so doesn't hold an edge well. However, if you can somehow deliver a few grams' worth of lead ... at high speed ... into a human body, and maybe repeat the operation a few times, they are sure to die...

Option 3: Neurotoxic darts or arrows

Use poison darts, rather than a knife. Much easier. Plus the distance gives you a head start in running away afterwards.

Option 4: Poisoned Traps

Look up Punji sticks... Has the considerable advantage of not having to face a large angry warrior eager to question you on your stabby motivations.

Why poisoned knives are a bad idea. Well, for one, you have to stab the person with it. Said person might violently object. Secondly, the person you stab tends to bleed out the envenomed blood. Thirdly, the person tends to die of stabbing-related causes before the poison can act. For these reasons poison is rarely used in melee weapons.

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    $\begingroup$ If you're going to bet that your opponent is letting you outwait the effects of lead posioning to work its way you're probably in trouble... unless you emphasise on that "high velocity" part of the trick ;) $\endgroup$ – Ghanima Feb 8 '15 at 22:05
  • $\begingroup$ @Ghanima, I'm thinking along the lines of "Eat lead, punk" $\endgroup$ – Serban Tanasa Feb 8 '15 at 22:06
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    $\begingroup$ That's why they say "Don't bring a knife to a gunfight", not even a poisoned one. Unless of course you are a Fremen. $\endgroup$ – Ghanima Feb 8 '15 at 22:10
  • $\begingroup$ You could try using an corrosive poison. If the poison melts the target, would you consider the person killed by the poison even if it was not due to poisoning? $\endgroup$ – grimmsdottir Feb 8 '15 at 22:47
  • $\begingroup$ @grimmsdottir good luck attacking your enemy with a melting blade! Most metals are vulnerable to corrosion (a notable exception is gold, that makes crappy weapons), and the most resilient materials are also brittle (glass and clay, mostly). $\endgroup$ – Davidmh Feb 9 '15 at 22:11

Frank Herbert's Dune presents the Fremen Crysknife to deliver a deadly poison from the tip. As the knife is made from the tooth of a sandworm the hollow once occupied by the tooth's nerve contains the poison. To deliver the poison to the enemy of course requires stabbing/impaling over slashing. The Fremen however are reported to avoid killing respected enemies with the tip (lucky ones!).

While it is not elaborated how a thickened liquid residing in the tip is quickly released in the wound the approach still offers some benefits: It does not require difficult additional coating of the blade and it does not enforce the use of a special sheath nor will it require any complicated unsheating procedures.

Bless the Maker and His water!


As an option, consider a bee-stinger style approach, with needle tipped fragments that break off in the opponent.

Interestingly enough, I don't think thickening the material is a good idea. Thickened material is only useful on the outside of the blade, for anything internal is too affected by capillary action. Poison on the outside of the blade would be hard to keep in combat (where metallic strikes could shake loose all but the most viscous fluids). The more viscous it is, the less likely it is to part from the knife and enter a wound. Less viscous solutions are more common in nature.

They also do not have to be lethal. Consider the stinging nettle, which is effectively covered in hypodermic needles full of acetylcholine, seratonin, histamine, and a host of other really nasty compounds your body uses to let yourself know you've been injured.


Normal melee weapons do not much benefit from poison for, among others, the reasons you mentioned.

However for an assassin poisoned weapons are still practical. This is because for a pro the weapon for killing the target and the weapons used to fight guards are two different and unrelated things. In fact, the preferred solution is not to need a fighting weapon at all.

The problem at this point becomes that if you want to avoid fightin, and you do, it is better to poison something the target eats, drinks, inhales, or touches. Because of this history had professional poisoners, but only professional "assassins" were religious fanatics making a point.

But if you assume some reason to attack the target instead of just poisoning them, fast paralysing neurotoxin that prevents guards from raising alarm would be useful.

The best solution, of course, is a ranged weapon. A blowgun, a dart, or a crossbow will allow assassins to disable guards from a range. This is made impractical if guards are wearing armor capable of stopping anything except crossbows heavy enough to be hard to conceal. Or if the target and guards are indoors.

Both darts and crossbow bolts can be used to stab targets from close range. Draw a dart, stab target, draw next dart, stab next target... There is no real value spending money on a dagger, if you will use poison anyway. If you don't need the option of throwing the disposable weapons far, metal spikes can be used. Possibly in the form of caltrops, which are quite useful in escaping.

Another option is poisonous dust that is blown to the face of targets, but that requires a level of care to use safely. Which implies you would be able to use poison the correct way of food, drink etc. Irritating dust can be used to distract guards while running away, though.

A weapon that injects poison or small poisoned darts to target is possible, but would only be used by a noble who wants a novelty item that might be useful in a pinch. A pro would simply use low cost disposable weapons that can be left to the wound.

There might be a separate fighting weapon, a short sword or large knife, or concealed armor for fighting. Just in case everything goes wrong and you need to fight. Assassins would general do this in groups with first rank using normal weapon to fight more or less normally while others throw poisoned darts or shoot crossbow bolts at the guards distracted by the fight or trying to raise alarm.


I can think of a solution - use acid instead of poison, and have a knife that functions like a hypodermic needle.

I can't find a good picture on the interwebs, but what I'm basically imagining is something akin to a rondel dagger, a stabbing oriented knife. However, swap out the handle for something more akin to a pistol grip, with an actual trigger. Upon stabbing your opponent with the knife, pull the trigger and pump him full of acid!

Now, the reason why I suggest acids over toxins - acids give you a more immediate effect. The shit burns and melts flesh. Its gruesome, terrifying and incredibly painful. Even if it (somehow) doesn't kill on the spot, you've basically won, because your opponent will be too in pain to fight back.

Then if you're feeling mean, just prick him on the arm with a tiny needle coated in @SerbanTanasa's suggested brachotoxin.

Append: An added bonus of my design - if the internal workings are powerful enough, you could spray it at an opponent at close range, giving you more reach. Alternatively, why use a rondel dagger when you could use an estoc?

  • $\begingroup$ The acid will likely corrode your blade too. And, since you would be carrying some sort of pouch of it, it would be a very tempting target for your enemy. $\endgroup$ – Davidmh Feb 9 '15 at 22:30

This isn't a complete answer but the knife would have to be oddly shaped, possibly barbed so that surface tension doesn't keep poison on the blade. It wouldn't be mechanical though, it would become to large, unwieldy and unreliable.


Preliminary skirmishes would be with suicide groups (kamikaze?) loaded with Polonium dust. Radiation poisoning is slow but the dose required is very small - and you don't have to inject it, breathing in the dust will do.

Once enemy troops have been exposed, follow Russian tactics of WWII (attack and fall back) and wait for winter ie. poisoning to take hold.

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    $\begingroup$ The proper weapon for applying polonium is, I believe, an umbrella $\endgroup$ – RedSonja Feb 9 '15 at 14:23
  • $\begingroup$ Actually, polonium is normally drunk in tea. $\endgroup$ – Blackbeagle Nov 29 '16 at 2:22

Consider the Bulgarian umbrella weapon. Tiny - microscopic ball coated in ricin and injected into unsuspecting dissident's leg via an airgun type arrangement. That or the use of radioisotopes in similar incidents - usually something like plutonium salts or polonium.

The nice advantage - stick, oops, sorry... - walk away. Days/weeks later the target drops dead and you're long gone.


Close combat venom can be usefull on a little combat more a battle. Much people are wounded but later healed. The venom can kill those soldies before the big battle will begin, days or weeks later.

Really sounds better any substance with instant action. Even doing a litle efect. A bit pain, your foe gets distracted a second...


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