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Poisons Used in Agatha Christie's Mystery Novels

Anne is an avid reader of Agatha Christie mysteries. Join her on a tour of poisons and toxins.

Agatha Christie often used poison to dispatch her victims.

Agatha Christie often used poison to dispatch her victims.

Foul Toxins From the Queen of Crime

“Poison has a certain appeal,” wrote Agatha Christie in They Do It With Mirrors, “…it has not the crudeness of the revolver bullet or the blunt instrument.” Death by poison is more frequent in Christie’s world than in the works of any other mystery writer. More than thirty victims fall foul to a variety of toxins (while others survive attempted poisonings). Christie’s knowledge was extensive, a result of her work as both a nurse and a pharmacy dispenser during both World Wars. (Perhaps this is why physicians often make an appearance as murders in her novels.)

Common Poisons

Strychnine is used in Christie’s first whodunit, The Mysterious Affair at Styles. For a writer, strychnine is an ideal poison, being easily absorbed with a rapid onset of action, and its effects are impressively dramatic. An alkaloid derived from the seeds of the tree Strychnos nux vomica, strychnine works as a competitive antagonist of glycine, an important inhibitory neurotransmitter. Strychnine blocks motor neuron post-synaptic receptors in the spinal cord’s central horn, antagonising inhibitory tone. Uncontrollable muscle contractions result, classically beginning with trismus and risus sardonicus, then spreading distally, with contractions increasing in frequency and intensity. Death occurs some two to three hours after exposure, most commonly from respiratory failure compounded by lactic acidosis and rhabdomyalysis.

Cyanide is the poison Christie used most often to dispatch her victims, (followed by arsenic, strychnine, digitalis then morphine). Cyanide is derived from the seeds of the Prunus family, (which includes cherries, apricots and almonds) and is rapidly lethal. It works as a mitochondrial toxin, inhibiting cytochrome c oxidase in the electron transport chain, thus preventing cells from aerobically using adenosine triphosphatefor energy. High concentrations leads to death in minutes; the cyanide-haemoglobin complex can cause the skin to remain pink (in contrast to the cherry-red of carbon-monoxide poisoning), despite cellular hypoxia. Chronic ingestion causes a variety of symptoms ranging from generalised weakness, confusion and bizarre behaviour, through to paralysis and liver failure. Cyanide features in The Mirror Crack’d from Side to Side, And Then There Were None, A Pocketful of Rye and, of course, Sparkling Cyanide.

Arsenic, favoured by the Borgias, makes an appearance in 4.50 From Paddington. A tasteless, odourless white powder, arsenic is minimally soluble in cold water but readily dissolves in hot fluids – such as tea or cocoa. Arsenic interferes with cellular longevity by inhibiting the pyruvate dehydrogenase complex, resulting in cellular apoptosis. Acute exposure generally manifests with watery diarrhoea, causing dehydration and hypovolaemic shock. Lactic acidosis and hypokalaemia can also occur. Arrhythmias include QT prolongation and ventircular fibrillation. Chronic toxicity is more insidious, with the clinical effects dependent upon the length of exposure. Hyperkeratosis and Mees lines on the nails are classical, as is a painful, glove-and-stocking paraesthesia. Hepatic and renal impairment may also result, and a patient’s breath often has a garlic smell.

Unusual Poisons

In The Pale Horse, the murderer uses a coven of witches to curse victims, thus masking deaths due to thallium (used in rat poison). Thallium can be absorbed topically, ingested or inhaled, is colourless and tasteless, dissolves in water, and has a slow onset of vague symptoms. The first signs are usually vomiting then diarrhoea, followed by a range of neurological symptoms. A fatal cardiac toxicity occurs some three weeks after adequate exposure. Hair loss is also common - which triggers suspicion in The Pale Horse .

In A Pocketful of Rye, marmalade is laced with taxine. (The murderer later puts cyanide in another victim’s tea.) Derived from the leaves of the English yew tree, taxine has a bitter taste. By disrupting microtubular function, it inhibits cell division. Death can be so rapid, however, that the common signs of a staggering gait, seizures, respiratory failure and heart failure may be missed. Most parts of the tree are toxic (save the aril surrounding the seeds, allowing distribution by birds without them being poisoned).

In Five Little Pigs, the painter Amyas Crale is murdered with coniine. An alkaloid extracted from hemlock, coniine works peripherally as a neurotoxin, causing death by respiratory paralysis. Less than two hundred micrograms is fatal; Socrates consumed this poison when condemned to death in 399BC for corrupting the youth of Athens.

In Cards On The Table, a doctor murders his victim by contaminating his shaving brush with bacillus anthracis, knowing the bacillus could pass transcutaneously through any nicks made by the razor. In Dumb Witness, the victim’s liver pills are doctored with phosphorus. The hint is given by the ‘aura’ seen around the woman: the phosphoresence of her breath. Exposure can also lead to ‘phossy jaw’, a severe necrosis common in workers in match factories, where white phosphorus was an early component. Severe liver damage can also result.

Monkshood dispatches several victims in 4.50 From Paddington. Described by the Roman naturalist Plinius as ‘plant arsenic’, it was once used to coat spears, prior to hunting panthers and wolves. It was also reputed to also kill werewolves, (although other sources claim a brew will prolong the lycanthropic condition when a werewolf is under the influence of the full moon). The active component is aconitine, which causes salivation, followed by vomiting, diarrhoea, respiratory failure and cardiac arrest.

Medical Poisons

Belladonna (also known as Deadly Nightshade, Devil’s Berries or Death Cherries) features in The Caribbean Mystery and The Big Four. Foliage and berries are toxic, containing a mixture of alkaloids including hyoscine (scopolamine) and atropine (both anti-cholinergic anti-muscurinic in action) and hyoscyamine (an isomer of atropine). Both the Emperor Augustus and Agrippina (wife and sister of Claudius) used belladonna to poison contemporaries. Symptoms include dilated pupils, blurred vision, tachycardia, dry mouth, slurred speech, urinary retention, confusion and hallucinations.

The anti-dote for belladonna poisoning is physostigmine, which is itself used as a poison in Crooked House, administered via eye drops. Derived from the West African calabar bean, physostigmine is a cholinesterase inhibitor, reversibly blocking the action of acetylcholinesterase in the synaptic cleft of the neuromuscular junction. Overdose results in the cholinergic syndrome, due to central and peripheral increase of acetylcholine at muscurinic and nicotinic receptors.

Morphine is another poison favoured by Christie. In Sad Cypress, morphine is administered through, it is thought, fish paste on sandwiches; instead it is served in a pot of tea, the murderer also drinking from the pot to ally suspicion, then surruptiously self-administrating an emetic. In Death Comes As The End, (set in Ancient Egypt), the poison added to the wine which kills Sobek is never discovered, but assumed to be the juice of the poppy. (The priest-physician tests the remaining wine on animals, all of which rapidly succumb.) The matriarch Esa meets her death by means of an ungent made of poisoned wool fat.

Murder mysteries would be incomplete without the use of sleeping tablets. In Lord Edgware Dies, Carlotta Adams meets her end due to an overdose of veronal. The first commercially available barbiturate, veronal had a slightly bitter taste, and a therapeutic dose far below the toxic dose. However, tolerance occurred with chronic use, requiring higher doses for effect, and fatal overdoses, either accidental or intentional, were not infrequent.

The Death of Hercule Poirot

Curtain, in which Poirot makes his final appearance, is a lesson in polypharmacy. (Poirot is the only fictional character to have been given an obituary in The Times.) Freda Clay poisons her aunt with morphine; Barbara Franklin is poisoned with physostigmine. Poirot drugs Hasting hot chocolate with sleeping tablets (unnamed, but possibly veronal) to prevent him committing murder; Mrs Franklin chooses the wrong coffee cup and dies from the poison she had added to kill her own husband; Poirot laces two cups of coffee with his sleeping tablets, so drugging Norton (who, suspecting, chooses Poirot’s cup) but not himself, as he is tolerant to the tablets. After shooting Norton, Poirot himself dies, not by poison, but by its absence: with terminal heart disease, Poirot places his supply of amyl nitrate out of reach, thus ensuring his own death during the night.

Agatha Christie’s writing reflects English life from the end of WWI to well after the Second World War. Despite the changing social mores, human nature is constant, and her writing offers an historical-social insight into this time. Most of the poisons used by her murderers were readily available, sometimes through their work, but more often to be found under the kitchen sink, or growing amongst the beauty of an English country garden.

© 2011 Anne Harrison


Anne Harrison (author) from Australia on November 19, 2017:

Cierra, Thank you! I keep re-reading her works, they are an absolute delight, and an insight into her times.

Cierra Fowler on November 13, 2017:

I have read all of Christie's works and loved them all. Definitely a must read for all!

Anne Harrison (author) from Australia on April 14, 2015:

Christie's works are interesting to read because they reveal so much about the time - as well as the mysteries to solve! Thanks for stopping by,


Diana Burrell-Shipton from Hubbard, Ohio, USA on April 14, 2015:

I have several of her books and am trying to collect them all. I like the books of this era in general, but hers are special because of the nuggets of realness in them. Trying to solve the mysteries get my brain working.

Anne Harrison (author) from Australia on March 20, 2015:

I'm glad you enjoyed it, Thelma. I never get tired of reading Agatha Christie, not just for the mystery but also for the insight into the world at that time,


Thelma Alberts from Germany on March 19, 2015:

What an interesting informative hub! I'm fond of reading Agatha Christie's books. Thanks for sharing.

Anne Harrison (author) from Australia on November 22, 2012:

I agree; on one hand they offer such insight to her times, yet in many many ways they don't date.

nina sharpe on November 20, 2012:

i think her books are wonderful,especially her use of poison!!!!

Anne Harrison (author) from Australia on December 04, 2011:

Thank you. I feel the same about Miss Marple!

Just History from England on December 03, 2011:

An analysis of Agatha Christie from a novel angle that adds a lot to my store of knowledge. I had not even considered the use of different types of posions, just thinking about it as a generic term. I did not read the last paragraph to the death of Poirot as to me, Poirot is still running around in London and the county looking for criminals!! Thankyou an enjoyable read, voted up and interesting

Anne Harrison (author) from Australia on November 30, 2011:

Many thanks for your comment. I've always enjoyed the historical context of her works, and I think the poisons used give an insight into that time. I'm glad you enjoyed it!

CountryCityWoman from From New York City to North Carolina on November 24, 2011:

What a brilliant hub! My sister and I have read everyone of Christie's books and I was always fascinated by the poisons. And yes, so many of them were readily available. I didn't know Poirot had an obituary in The Times. How very clever. We missed that here in New York City.

I so enjoyed this hub.

Thanks a million and rated way up! Yay!