The Physiology of Poison

A while ago I was talking to a friend about pop culture pet peeves–those things that really bother us when we’re watching or reading something. And when she asked me what mine was, my answer was immediate: poison. Specifically when someone eats or drinks a poisonous item and collapses 3 seconds later. And today I’m going to talk about why and how to avoid it in your own writing. 

For some background, I was a bio major–specifically a neurobiology and physiology major. Fair warning: my knowledge of pharmacology/pharmacodynamics is pretty basic, but I’ll do my best to explain why if your character eats that poisoned cake, it’s going to take them a hot minute for them to start feeling any effects.

Before we begin, here’s quick physiology recap. Blood carries oxygen and other molecules to cells. Deoxygenated blood flows into the heart, the heart pumps the blood to the lungs where it becomes oxygenated, then the heart pumps blood to the organs, which then returns to the heart after it has been deoxygenated. Got it?

So why does it bother me when people collapse quickly from poison? It actually has to do with how the poison was administered. The three most common* ways to administer any drug are inhalation, intravenous injection, and ingestion.

Let’s start with ingestion. So your character eats a piece of poisoned cake. What happens next? Probably nothing** for a while. They’ll eat it, they’ll digest it, and then it’ll get absorbed from the stomach and intestines into the bloodstream. And just like how much food you have in your stomach affects how quickly that buzz from alcohol hits you, how much food is in the character’s stomach is going to affect how quickly the poison is digested and absorbed into the blood. Generally, this process is going to take 20-30 minutes.

Once the poison’s in the bloodstream, remember, it has to go back to the heart and the lungs before it’s sent back out to the organs with the poisonous molecule. And it’s only after enough poison has been absorbed into the blood and circulated back out to the organs for the character to start feeling those deadly effects. Which is why in most cases, it’s totally unreal for someone to eat a bite of poisoned cake and collapse a few seconds later!

But that doesn’t mean it’s impossible to immediately see effects from poisoning. Intravenous injection works quite quickly. Of course, for this to work, we’re assuming that the character who is administering the poison or drug knows how to find a vein. Once the poison in the veins it will return to the heart, the lungs, then back to the organs. It’ll take a little bit of time for enough of the poison to start working, but we’re looking at a timeline of few minutes now. By introducing the poison directly into the bloodstream, we’ve cut out the long process of absorption.

But the fastest route to administer any poison is inhalation. When you inhale air, it’s going directly into your lungs. And if the poison is in the lungs, it can immediately be sent to the heart and pumped out to the organs. We’ve basically cut out half the cycle when the blood from the organs returns to the heart.

And this applies whether your character has been given a drug or potion or magical concoction. Always think about how it’s getting into their system and how that’s going to affect the timeline of when they’ll feel the effects. 

I know this seems like such a minor detail, but research is a key component of writing. Whether it’s science and medicine, other cultures, or historical facts, it’s important as much as possible to get those little details right.

Of course, we all make mistakes. We might not always get every single detail right, especially if we don’t have a background in that specific field. But for me, a lack of research indicates a lack of care. It’s easy to say “well, everyone else just does it this way,” and call it a day, but it shows when writers are willing to dig deeper. Not only does it lead to a richer experience for readers, it shows how much the writer cares about their craft and story.

Note: I understand that this is a slightly more scientific post than we do. If you have any questions, please don’t hesitate to leave a comment. I’m not an expert by any means, but I’ll do my best to answer questions or point you toward resources. Happy (fictional) poisoning, friends!

*there are other routes of administration like sublingual, topical, intramuscular etc. but in the interest of keeping this fairly simple, I decided to focus on the most commonly used routes.

**this is getting into poisoning 201 territory, but there are some digestive enzymes in the mouth and depending on the poison/drug, they might break down enough to be absorbed into the capillaries from the mouth to directly and quickly enter the bloodstream that way. Assuming there’s a large enough concentration absorbed, you can potentially see really fast effects.

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