Image by Anthony Kelly used under CC BY 2.0 (cropped)

I mean in your stories, of course. The correct way to use them in real life is simple: don’t. In stories, on the other hand… well, your characters have to face death at some point. Why not let chemistry help? Ah, but not all poisons are created equal, and not all poisons will be available in all settings for your murderous plot devices.

Different Poisons for Different Times

Depending on the time period or tech level, different types of poisons will be available to your characters. How “advanced” the poison is can be grouped into three general classes:

Gifts of Nature

The earliest – and still classic – poisons were simple herbs, animal secretions, and the occasional mineral. By careful observation or (more likely) tragic experimentation, early humans discovered naturally deadly substances in the world around them. Little to no understanding of these poison’s underlying function was required. Did the enemy die quicker when hit by an arrow dipped in the secretions of that pretty frog? Yes? Great! Let’s keep doing that, then. Do deer avoid eating that funny-looking weed? Let’s feed it to our rival and see what happens! Nature is full of all manner of quirky, toxic substances, and pre-historic cultures were remarkably aware of them. In fact, the earliest human “professional” was the tribal healer, shaman, or witch-doctor: a person who was thoroughly acquainted with all manner of natural poisons and remedies – though the former were generally more reliable than the latter.*

Poisons derived from plants and animals often trump minerals in terms of raw deadliness. They have been optimized by millions of years of evolution to target (and mess with) a specific biological function. Plants and animals like to avoid getting eaten, and killing anyone who dares nibble them is a great way to accomplish this – at least, until the predator evolves resistance. Some of these substances merely cause vomiting and general discomfort; others are highly potent neurotoxins which can prove fatal in minutes.

Gifts of the Garden and Alchemy

Once a civilization grows large or prosperous enough to support a networked class of healers, it opens up access to more than just raw herbs and secretions. Many cultures slowly gained a practical knowledge of how to grow, blend, administer, and apply all manner of natural materials to create different effects. Some of these concoctions resembled the potions so common in medieval-esque fantasy settings – especially games.* Unlike games, healing tonics could be unreliable – but poisons? Those were easy. In fact, they were typically just the “healing” herbs at higher doses. Nightshade/Belladonna, Mandrake, and Monkshood/Aconite were all plants that a local apothecary or herbalist could grow or collect – all justifiable tools of the trade, and all highly convenient for would-be assassins.

With access to pure (or at least high-proof) alcohol and other solvents came the ability to extract and concentrate the essences* of minerals, animals, mushrooms, and especially plants. Tinctures* of aconite were much more efficient than the raw plant – one teaspoon in the mark’s whiskey would get the job* done. Alcohol extraction and other early alchemical techniques could also be used to refine existing mineral-based poisons into more concentrated, soluble, or undetectable forms. (For example, more pure and water-soluble compounds of arsenic – most notably arsenic trioxide.)

Gifts of Laboratories and Industry

The early industrial period was notable in that a proper understanding of chemistry had not yet been achieved,* yet industry* was producing and using unnatural chemicals on an unprecedented scale.

Only recently have chemists produced entirely novel compounds for use as lethal poisons. The average American has more bottles of toxic chemicals in their house* than an entire medieval apothecary. Not to mention the staggering inventory of lethality on display at any drug store, garden center, or high school chemistry lab. An overwhelming assortment of the deadliest poisons – both synthetic, and isolated from rare species in exotic locations – have become available to poisoners everywhere. Poisons, thankfully, have been made largely irrelevant by modern forensic toxicology.* But modern poisons are like modern weapons or any other sufficiently advanced technology: if we could take it back in time, we’d have a hey-day.

Real Poisons, Fantastic Settings

Like dueling and piracy, the golden age of poisoning is behind us – but that doesn’t mean poisoning has been exterminated. Nobody can stop poisoning per se; the authorities can merely provide a strong deterrent. Poisoners are probably going to get caught, and so the incentive is no longer there. At least, not for rational people.

Poisons out of place and time

So let’s talk fantasy here: what happens when a modern poison is taken back in time, to an era before forensic toxicology? Or, since we can travel in space much more easily than time, what happens when an assassin takes a poison from one region and uses it in another, where either the poison or forensic toxicology are unknown? It’s simple: that assassin can kill more people. The targets will have little hope of finding antidotes, and local authorities will have significant difficulty in locating and stopping the perpetrator. In fantasy settings as well as reality, the more exotic the poison, the better.*

Let’s explore the geographical quirks associated with poisoning a bit further. Scientific advances would not be necessary for a culture to achieve a richer repertoire of poisons. A few minor changes in the flow of migration, trade, or biology could have brought ridiculously potent poisons to cultures with the know-how to extract and concentrate them (most notably, late medieval Europe). Poison-dart frogs and their* magnificently potent batrachotoxin could have been native to Europe.* A commonly available nerve agent of this power would have had a dramatic impact on medieval European history.

A primitive society with easy access to radioactive materials* would learn to respect these materials – and use them to kill. They might be named after gods (or demons) of death, decay, or evil.

And finally, a bizarre case of a “recent” poison is botulinum toxin, the most acutely toxic poison known to modern science.* Clostridium botulinum bacteria has been present in air-deprived* soils around the world since well before humans existed. However, it was only positively identified in 1895 – and isolated much more recently. Knowledge and use of botulism toxin by an early society would have required not just well-developed chemistry, but also biochemistry: on Earth, a late-blooming sub-field of a late-blooming field of science. I for one am grateful that this ubiquitous organism has only become well-understood in recent times; an early understanding of botulism* would have made things a little too interesting. Luckily, authors and worldbuilders are all about interesting.

Different Poisons for Different Purposes

Different jobs require different poisons. Does your poisoner need to assassinate the king without getting caught? Take her own life along with dozens of her cultist followers? Poison the village’s water supply so its elders will hand over the protection money? These different tasks have different requirements, and thus different poisons are optimal. For poisoning the village well, anything bitter and mildly toxic will do; your poisoner doesn’t actually want to kill off (m)any villagers or they can’t pay him to go away.* The poison your assassin will need to kill the king must be as tasteless and traceless as possible, while a poison for the cult leader and followers can be bitter – but should be fast-acting and painless. And if a character needs a creepier flavor of evil, she can feed someone a long-acting, biocumulative poison like arsenic so that the target becomes increasingly ill over time. (Inefficient, but potentially appealing to sadists and those who seek to foster a dependence.)

There are other considerations that go through the minds of poisoners, and should therefore be going through the minds of authors who create them:

How fast-acting is it?

Poisoners often want to be a long, long ways away before someone dies. But sometimes a quick and confirmed kill is important – or someone’s passing needs to be eased as mercifully as possible. A wise poisoner will choose the appropriate tool for the task at hand. For slow, painful, and irreversible: give deathcap mushrooms a try. Need someone dead NOW? Cyanide is the best historically-available option, but don’t rule out natural neurotoxins if they’re available.

How is it applied?

Most poisons must be absorbed internally, as the skin is a formidable barrier to chemical agents. Though a rare few substances are potent or skin-penetrating enough to be fatal via touch* or inhalation,* almost all poisonous substances must be delivered via food or drink. Since evolution has equipped us with a means of detecting many dangerous chemicals, generally via bitterness, the smell and taste of most poisons must be masked.

What about blades? The skin is, of course, a less formidable barrier against very sharp objects.

Melee weapons were poisoned only very rarely. Blades can inject poison directly into the circulatory system – but only in small amounts. By the time most cultures had discovered poisons potent and fast-acting enough to have any impact in battle, machine guns and mortars rendered such considerations moot. A faster and more effective way to double the damage of a stab wound? A second stab wound. Not to mention, all that poison hanging around on a blade was an occupational hazard.

Ranged weapons, however, are a different story. Even a good archer can’t always kill a target with a single hit. That foot soldier the sniper shot in the shoulder can probably still kill her. But if the sniper applied a good enough poison to her arrow, the soldier’s prospects for staying alive long enough to reach the sniper are diminished. And in a long, protracted battle or a grueling war of attrition, poison is still useful if it’s very slow – or replaced with a mere infectious agent.* Darts were an even more common delivery method, especially in regions such as the Amazon rainforest where very potent natural poisons were available. Darts don’t deal much damage on their own, but are great delivery agents for deadly poisons.

Direct application via syringe is also an option for post-medieval assassins. If a would-be murderer has easy access to their target and a syringe in hand, poison is probably redundant – just inject the target with the empty syringe. “Empty” being a misleading word, as the syringe is full of a very unlikely poison: air. (Inject directly into the carotid artery or heart for guaranteed lethality.)

If your character is not an assassin but a terrorist or extortionist, they can just dump something toxic in the nearest well or granary, and the “delivery method” is moot.

How much should be used?

The dose makes the poison.* In fact, this is precisely the reason poisons were commonly available even many centuries ago:* poisoners didn’t have to buy poison per se. They bought medicines and herbicides, and either extracted out the “good bits” or, more likely, just used a much higher-than-suggested dose.

Frequently, the sellers knew what their products would be used for, and even optimized their lethality while marketing them as cosmetics or other products.

And while we’re discussing dose size, it’s worth remembering that recreational drugs and alcohol* are all poisons. Quantity can replace quantity. An assassin might not need to add anything to his mark’s liquor besides more liquor.

How easy will it be to diagnose?

This is perhaps the most important point – the one thing that will be on the mind of every half-competent poisoner.

Did you use a substance most people – or at least most doctors – are readily familiar with? Worse yet, do people know you have access to this substance? If your landlord’s symptoms were obviously those of oleander poisoning, and you grow oleander in your front yard, you’re either being framed or just not too bright.

It’s also prudent to consider current events when carrying out an assassination. For example, arsenic poisoning was favored during cholera epidemics, because to many people, the symptoms of arsenic poisoning were indistinguishable from those of cholera. For poisoners operating during the heyday of the frantic European witch-hunts, potential “witches” made for excellent scapegoats.

As modern chemistry led to modern forensic toxicology, the arms-race between poisoners and law enforcement escalated. Forensic toxicology first became legitimized with the Marsh Test for arsenic, in early 19th century France. Later, in the early 20th century, the greatest advances were being made by the police department of New York City. Though the struggle was long-fought, the result has been a near-total victory for forensic toxicology. Nowadays, the poison used to kill or disable a target can almost always be identified – so long as poison is suspected in the first place.*

Is there magic?

This subject proved, understandably, more difficult to research. Yet I can feel confident in saying: magic is probably way better than poison.

It depends on your magic system, of course, but magic is often depicted as doing everything poison can do – in addition to healing or preventing poison damage. Magic – especially divine and mystical forms of magic – doesn’t tend to care how complex human biochemistry is. If your world or story combines both poison and magic, be careful to limit your magic system so that poisons are still relevant. Another possibility is the existence of anti-magic poisons to help level the playing field.

Examples of Commonly-Used Poisons


Oleander. A pretty flowering shrub with good drought tolerance, Oleander (or Nerium) is grown throughout the southern United States – most notably as a median plant in freeway dividers. As if freeways needed to be more lethal.

Hemlock. Also known as Conium; no relation to the tree named hemlock. This poisonous plant quickly causes total paralysis after ingestion of just six to eight leaves. Death is via asphyxiation, since breathing doesn’t work if all your muscles are turned off. The “antidote” is simply the use of a respirator, for about a day’s worth of breathing-by-machine. Unfortunately, Socrates did not have access to this technology.

Digitalis/Foxglove. These beautiful, colorful flowers contain potent cardiac glycosides, which affect the function of the heart. Digitalis is both a useful medicinal herb and a potent, literally heart-breaking poison.

Aconitum / Monkshood / Wolf’s Bane. This plant is used around the world in traditional medicines and to poison arrows or spears for hunting. Traditional Indian and Chinese medicine have processes to detoxify the plant before use. Without this process, it is a deadly poison – and at high doses, it acts remarkably quickly for a plant-based poison.

European Yew. This long-lived, culturally significant tree has deadly berries and deadlier foliage. Symptoms of poisoning may be entirely absent – munch on yew leaves, and you could just drop dead in an hour. Fun fact: the red outer coating (the aril) is perfectly edible. It’s a bit like gooey jello, sweet and gum-like. Just don’t accidentally eat the seed inside!

The yew was scarce throughout late medieval and renaissance Europe due to enormous demand, especially from England, for its wood in making longbows of the highest quality.

Rosary Pea, or Jequirity. This deadly invasive species has a pan-tropical range, though it originated in Indonesia. It contains abrin, one of the deadliest natural poisons, which works by shutting off the cell’s protein-building machinery. Symptoms normally don’t even occur for at least eight hours, but even one of these bright-colored peas is enough to kill an adult human. Painfully. (Caveat: intact peas may pass through the digestive tract without releasing their toxin; crushing or damaging the peas is required for toxicity.) Fun fact: the plant is invasive throughout nearly half the planet, its hard glossy peas are commonly used as beads,* and they are attractive to children. (I’ll let you figure out all the implications on your own.) If your assassin is the type to wear a necklace, a necklace of brightly colored rosary peas could be a practical choice. (You can buy 200 of them for 10 bucks on eBay! As if we didn’t have enough access to cheap poisons.)

If your story isn’t set near the tropics, consider misteltoe as an alternative: it isn’t quite as toxic overall, but it contains the same general type of poison. Ditto with the castor bean, source of ricin.

Mandrake. A treasure-trove of bizarre mythology surrounds this plant: it screams when unearthed, it can only grow where the semen of a hanged man has landed, and other such oddities. These stories could be inspired by the human-like shape of the thick, bifurcated roots, or perhaps by the fact that it’s chock-full of poisonous hallucinogens.

Though the roots are filled with poisonous hallucinogenic and hypnotic alkaloids, they can have arguably beneficial properties at low doses. Not to mention, mandrake berries are edible, so peasants and herbalists had a justification for growing this plant.

Suicide Tree. Cerbera odollam, native to India and other parts of Southern Asia, is the most common plant-based suicide aid, and is presumed to be the reason that the suicide rate in Kerala, India is three times the expected value. It’s also a surprisingly good murder weapon which modern toxicologists can miss. It was also responsible for the deaths of 2% of the population of central Madagascar per year, due to its use as an ordeal poison* until 1861.

Calabar beans. Another common ordeal poison from Calabar, now part of modern Nigeria. Unfortunately, calabar beans look just like any other generic, nutritious legume; a toxicology hazard more common in berries. Pro tip: if anyone asks you to prove your innocence via immunity to poison, start looking for a less painful way to die.

Belladonna / Nightshade. One leaf or five delicious berries of nightshade is typically sufficient to kill a grown person. And yet, at low doses, its extracts have had a number of uses ranging from legitimate to dubious – from treating gastrointestinal disorders, to dilating women’s pupils to increase seductive appeal.

Nightshade was common in Europe throughout its history, and its toxic effects could be identified, for both antidote use and incrimination of perpetrators. Thus, despite its high potency, it was often an unwise choice for assassins. It was more likely to terminate unsupervised foraging children than high-value political targets. It was one of the select few poisons known to be used in ranged weapons, however – nightshade-tipped arrows were used in ancient times. Nightshade may have damaged the reputation of the tomato, a related – and much healthier – plant; 16th century Europeans were convinced that tomatoes were poisonous.

Nightshade contains a class of poison – called an anticholinergic – whose antidotes are simply an opposite class of poison; cholinergics.

Strychnine. From the Strychnine tree, also known as the Nux Vomica tree. Though it received widespread use throughout Asia, it was not concentrated into the infamously potent modern poison until just a few hundred years ago.

It was popular throughout the early 1900s as a rat poison, but like most poisons that target mammals, it is remarkably lethal to humans as well. Though it has been used in a number of forms of traditional medicine, none of these applications appear justified – except for the traditional Indian method of raising blood pressure, for which there are safer modern methods.

Destroying angel and Deathcap mushrooms. These two fungus species contain deadly amatoxin. This poison is slow-acting – symotoms take between five hours and a day to manifest – but difficult to reverse. Ingesting just one mushroom is typically lethal. These mushrooms are predominantly an environmental or accidental poison,* but were occasionally used in assassinations, especially in ancient times.

Potions and Substances

Concentrated ethanol. High-proof liquor has been a source of significant poisoning since the advent of distilling. But its impact ranges much farther as the first commonly available organic solvent. If a culture had access to strong drink, a “powered up” version of any of the plant poisons could then become available.

Cyanide. The leaves and pits of cherry, almond, nectarine, peach, apricot, and plum trees contain sugar-like molecules that release dangerous amounts of cyanide when damaged. However, only during the early industrial era did cyanide become an efficient poison.

Early dyemakers were heavily involved with cyanide (which bonds tightly to certain metals to form deeply colored dyes), though they weren’t fully aware of what they were dealing with until chemistry as a science became more advanced. Conveniently, most cyanide-containing dyes are fairly safe, as the cyanide remains strongly bound to a metal atom.

Adding acid to cyanide-containing compounds, however, can form hydrogen cyanide, an acidic gas. Along with carbon monoxide and a few rare nerve agents (sarin and its ilk), the hydrogenated form of cyanide is one of the only potent gaseous poisons which have the potential to cause mass fatalities.

Arsenic. This element has been available since antiquity, although it occurs rarely in pure elemental form. Alchemists eventually learned how to roast arsesnic-containing minerals such as beautiful realgar to produce deadly, efficient arsenic trioxide. Arsenic trioxide is water soluble (especially in alkaline water), and was untraceable until the 1800s. Arsenic works both as an acute, slow-acting poison and a long-term, bioaccumulating toxin like lead or mercury. Arsenic poisoning isn’t always a one-time deal; it is frequently a long, drawn-out process where nature itself plays the role of assassin – often in the form of contaminated groundwater. Many common toxic hazards contain arsenic, though less so now that we’ve stopped using arsenic and its compounds to make food colorings, medicinal tonics, and cosmetics.

Thulium. This soft gray metal tricks your body into thinking it’s potassium.* Thulium was formerly used in rat poisons.

Thulium was known as a “poisoner’s poison” or, along with arsenic trioxide, “inheritance powder,” and it’s one of the few practical pure elemental poisons. Plutonium is ridiculously toxic even without counting the radioactivity – but really now, where are you going to get plutonium? Mercury, lead, and other heavy metals are slow bioaccumulators, which are poor tools for assassins. Others, like fluorine, can NOT be isolated or stored without special equipment. A poison is not so useful if it explodes and kills YOU.

Mercury Cyanide. This dangerous-to-handle substance is a great example of two wrongs making a much, much worse wrong. Synergy is the word here: this poison provides all the “benefits” of fast-acting cyanide and permanently-damaging mercury, with the added bonus of skin permeability and volatility.

Modern Chemicals

Household chemicals. Most common household chemicals in the wrong proportions and/or wrong mixtures can be toxic – though they tend to make inefficient poisons. However, quantity and availability can trump quality. Antifreeze made from ethylene glycol is particularly noteworthy, since it’s so sweet and palatable. It’s a common accidental poison for children and dogs, who think it’s wondrously fortunate that such a delicious treat was spilled in the garage. A combination of household ammonia and bleach will produce toxic fumes containing hydrazine and other nasties. If the ventilation is poor, this combination can be deadly.

Radioactive isotopes. Many of these can be highly toxic, with the most notable being polonium. Plutonium is also highly poisonous, but it’s roughly equal parts radioactivity and straightforward chemical toxicity.

Drugs. Overdoses of various drugs invented or modified by the pharmaceutical industry are a common occurrence in the modern era. Overdoses aren’t new, but chemists are designing these molecules from scratch, and they tend to be much more effective than the natural stuff. One of the most notorious is fentanyl.

Neurotoxins. Potent and volatile* neurotoxins are practically a hallmark of the modern era. They include synthetics like the VX series and sarin. Though these nerve agents are ridiculously poisonous, most of them aren’t record-breakers; rather, they’re especially scary because they combine high lethality with a tendency to form vapors. They’re less useful for targeted assassinations than they are for chemical warfare and terrorism.

Scientific accuracy – or at the least, an aura of plausibility – can go a long way toward preserving a reader’s suspension of disbelief. Instead of inventing fantastic and inexplicable poisons, you can dress up real poisons with new names. An early-medieval society which has discovered how to produce pure cyanide could name the chemical “essence of cherry”, “devil’s bitters”, or “dyemaker’s blight.” While poisons can be complex, the feeling of authenticity only requires familiarity with the basic classes of poison and their usage.


Further Reading

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