This list covers 18 poisons, running alphabetically from “Oleander” to “Oscillatoria.” They come from a wide range of sources, including garden plants, venomous animals, industrial chemicals, and mold that grows on stored food. Some show up in medicine cabinets and pesticide sheds, while others are simply part of the natural world around us, in gardens, forests, and ponds.
Poisons are substances that harm the body when they enter it in enough quantity, whether through eating, breathing, or skin contact. Some act within minutes, while others, like certain mushroom toxins, stay silent for days before causing damage. Ouabain has a particularly striking history: African hunters once used it to coat arrow tips for hunting large game.
Below you’ll find the table with Poison, Source, Effects, Antidote, and Description.
Poison: the common name of each substance, so you can quickly find the one you’re curious about.
Source: where the poison comes from, whether a plant, animal, mineral, or man-made chemical.
Effects: what happens to the body after exposure, from mild irritation to life-threatening symptoms.
Antidote: the treatment or substance that can counteract the poison, when one exists.
Description: a short explanation that gives you context on where the poison is found and why it matters.
Poisons
| Poison | Source | Effects | Antidote |
|---|---|---|---|
| Oleander | Nerium oleander plant (leaves, flowers, sap) | Nausea, vomiting, irregular heartbeat, can be fatal | Digoxin immune Fab, activated charcoal |
| Opium | Dried latex of the opium poppy (Papaver somniferum) | Slowed breathing, sedation, coma, death in overdose | Naloxone |
| Oxycodone | Semi-synthetic opioid painkiller derived from thebaine | Respiratory depression, drowsiness, overdose death | Naloxone |
| Orellanine | Cortinarius mushrooms (e.g., fool’s webcap) | Delayed kidney failure, days after eating | No specific antidote; dialysis |
| Ouabain | Seeds and bark of African Strophanthus and Acokanthera plants | Heart arrhythmia, vomiting, cardiac arrest | Digoxin immune Fab |
| Osmium Tetroxide | Oxidized osmium metal, used in labs | Severe eye and lung damage, blindness | No antidote; supportive care |
| Oxalic Acid | Rhubarb leaves, spinach, and other plants | Kidney damage, low blood calcium, mouth burns | Calcium gluconate |
| Organophosphates | Synthetic pesticides and insecticides | Overstimulated nerves, seizures, respiratory failure | Atropine and pralidoxime |
| Orpiment | Arsenic sulfide mineral | Vomiting, organ failure, arsenic poisoning | Dimercaprol (chelation therapy) |
| Ordeal Bean | Seeds of the Calabar bean plant | Muscle paralysis, seizures, cholinergic crisis | Atropine |
| Ozone | Reactive gas formed from oxygen, industrial byproduct | Lung irritation, chest pain, breathing difficulty | No antidote; oxygen and supportive care |
| Onion | Allium cepa, a common kitchen vegetable | Toxic to pets: anemia and weakness; mild irritant to humans | No specific antidote for pets; veterinary care |
| Oak Acorns | Acorns and young leaves of oak trees | Kidney damage, digestive upset in livestock | No specific antidote; supportive care |
| Octopus (Blue-Ringed) | Venom glands, delivered by bite | Paralysis, respiratory failure | No antidote; mechanical ventilation |
| Oxytropis (Locoweed) | Toxic rangeland plants in the Oxytropis genus | Nerve damage and disorientation in livestock (“locoism”) | No antidote; removal from pasture |
| Ochratoxin A | Mold growing on stored grain, coffee, and dried fruit | Kidney damage, immune suppression | No antidote; supportive care |
| Ordeal Tree | Bark and seeds of the Erythrophleum tree | Heart and digestive toxicity, vomiting | No antidote; supportive care |
| Oscillatoria | Toxic blue-green algae blooms in freshwater | Liver damage, nerve toxicity in animals | No antidote; supportive care |