This list covers 18 poisons, from “Ricin” to “Rye Ergot.” They come from plants, animals, minerals, and manufactured chemicals, and many have played surprising roles in medicine, agriculture, pest control, and even industrial products people use every day.
Poisons are substances that harm or kill living organisms when they enter the body in sufficient amounts. Some occur naturally in plants and venomous animals, while others are man-made compounds created for farming, manufacturing, or pest control. One striking example is rhododendron toxin, which causes “mad honey disease” when bees turn its nectar into honey.
Below you’ll find the table with poison, source, effects, antidote, and description.
Poison: the name of each toxic substance featured on this list, so you can quickly find the one you’re researching.
Source: where the poison comes from, whether it’s a plant, animal, mineral, or synthetic chemical, so you understand its origin.
Effects: the physical symptoms and health effects the poison causes, helping you recognize what exposure might look like.
Antidote: the treatment or remedy available for poisoning, if one exists, so you know what response is possible.
Description: extra background on each poison, including its history, uses, or notable cultural facts that add context.
Poisons
| Poison | Source | Effects | Antidote |
|---|---|---|---|
| Ricin | Castor bean (Ricinus communis) | Blocks protein production in cells, leading to organ failure and death | None; supportive care only |
| Rotenone | Roots of tropical plants like Derris and Lonchocarpus | Starves cells of energy, causing nausea, vomiting, and respiratory failure in high doses | None specific; supportive care |
| Rattlesnake Venom | Bite of a rattlesnake | Destroys tissue, causes swelling, internal bleeding, and can trigger shock | Antivenom (CroFab or similar) |
| Red Squill | Bulb of the sea squill plant (Urginea maritima) | Disrupts heart rhythm, causes vomiting and cardiac distress | No specific antidote; treated like digitalis toxicity |
| Rhododendron Toxin | Nectar and leaves of rhododendron and azalea plants | Causes dizziness, vomiting, low blood pressure, and irregular heartbeat | No specific antidote; atropine may help with heart symptoms |
| Ronnel | Synthetic organophosphate pesticide | Overstimulates the nervous system, causing tremors, sweating, and breathing trouble | Atropine and pralidoxime |
| Roundup (Glyphosate) | Widely used synthetic herbicide | Irritates the gut and skin; large doses can cause organ damage | No specific antidote; supportive care |
| Rue | Leaves and oils of the rue plant (Ruta graveolens) | Causes skin burns in sunlight and liver or kidney damage in large amounts | No specific antidote |
| Russell’s Viper Venom | Bite of the Russell’s viper | Causes uncontrolled bleeding, kidney failure, and tissue death | Antivenom |
| Radium | Naturally radioactive metal found in trace amounts in the earth | Damages bone marrow and DNA, raising cancer risk over time | No true antidote; chelation therapy may reduce body burden |
| Radon | Radioactive gas released from decaying uranium in soil and rock | Damages lung tissue with prolonged exposure, raising lung cancer risk | No antidote; prevention through ventilation |
| Red Phosphorus | Industrial and match-making chemical | Irritates skin, lungs, and eyes; ingestion can damage internal organs | No specific antidote; supportive care |
| Reserpine | Extract of the Rauwolfia serpentina plant | Causes dangerously low blood pressure, slow heart rate, and depression | No specific antidote; supportive care |
| Rhubarb Leaves | Leaves of the rhubarb plant | Causes kidney damage, vomiting, and stomach pain | No specific antidote; calcium may help |
| Ryanodine | Extract of the Ryania speciosa shrub | Disrupts muscle and nerve calcium signaling, causing paralysis | No specific antidote |
| Ragwort | Common ragwort plant (Senecio jacobaea) | Causes slow, irreversible liver damage with repeated exposure | No specific antidote |
| Rattlebox | Crotalaria plant seeds and foliage | Causes progressive liver damage and lung changes over time | No specific antidote |
| Rye Ergot | Fungus (Claviceps purpurea) growing on rye and other grains | Causes hallucinations, convulsions, and restricted blood flow to limbs | Vasodilators and supportive care |
Descriptions
Ricin
One of the deadliest natural toxins known, ricin is extracted from castor beans and has even been used as a weapon in real-world assassination attempts.
Rotenone
Once a popular natural pesticide and fish poison, rotenone has been linked to Parkinson’s-like symptoms with chronic exposure and is now heavily restricted.
Rattlesnake Venom
Injected through a rattlesnake’s fangs, this venom breaks down blood cells and tissue, making prompt antivenom treatment critical after a bite.
Red Squill
Long used as a rat poison, red squill contains heart-affecting compounds similar to digoxin, making it dangerous to pets and livestock too.
Rhododendron Toxin
Known as grayanotoxin, this plant compound famously causes “mad honey disease” when bees make honey from rhododendron nectar.
Ronnel
A once-common flea and tick treatment, ronnel belongs to the same chemical family as nerve agents, though far less potent.
Roundup (Glyphosate)
The world’s most widely used weed killer, glyphosate is generally low in acute toxicity but has sparked long-running debate over cancer risk.
Rue
This bitter herb was once used in folk medicine, but its oil can cause severe skin burns when exposed to sunlight.
Russell’s Viper Venom
Responsible for more snakebite deaths in Asia than almost any other species, this venom disrupts blood clotting throughout the body.
Radium
Once painted onto watch dials by hand, radium’s radioactivity caused devastating illness among the “Radium Girls” who worked with it.
Radon
This invisible, odorless gas can seep into basements and homes, making it the second-leading cause of lung cancer after smoking.
Red Phosphorus
Used in matches and fireworks, red phosphorus is far less reactive than its white form but still hazardous if mishandled or ingested.
Reserpine
Once a common blood pressure medication, reserpine in overdose can slow the heart and nervous system to dangerous levels.
Rhubarb Leaves
While rhubarb stalks are a popular pie ingredient, the leaves contain high levels of oxalic acid that can seriously harm the kidneys.
Ryanodine
Once used as a natural insecticide, this plant compound interferes with how muscles contract at the cellular level.
Ragwort
A common roadside weed, ragwort is notoriously toxic to horses and cattle, gradually destroying the liver if eaten regularly in hay or pasture.
Rattlebox
Grown historically as a cover crop, rattlebox seeds contain liver-damaging alkaloids that pose a slow-building risk to grazing animals.
Rye Ergot
Historically blamed for outbreaks of mass hysteria and gangrene in medieval Europe, ergot-contaminated grain remains the ancestor of modern LSD research.