This page lists all 18 poisons in our directory that start with the letter I, ranging from “Iron (Ferrous Sulfate)” to “Isoflurane.” These substances turn up in everyday places like medicine cabinets, garden sheds, and even backyard plants, and most of them serve a legitimate purpose, whether that’s treating an illness, protecting crops, or keeping surgery patients safely unconscious.

Poisons are substances that harm the body when they enter it in the wrong amount or the wrong way, even ones that are otherwise helpful in small doses. Iron supplements save lives every day, yet iron overdose remains one of the most common accidental poisonings among young children, a reminder that too much of something ordinary can turn dangerous fast.

Below you’ll find the table with the poison, its source, its effects, its antidote, and a description.

Poison: the name of the substance, so you can quickly find the one you’re looking for or scan the full list.

Source: where you’re likely to encounter this poison, such as a medication, plant, or household product.

Effects: the symptoms it causes in the body, so you know what to watch for and can recognize a possible exposure.

Antidote: the treatment used to counteract it, or a note that only supportive care is available.

Description: a short explanation of how the poison works and why it matters, with context you might find useful.

Poisons

PoisonSourceEffectsAntidote
Iron (Ferrous Sulfate)Iron supplements, prenatal vitaminsVomiting, GI bleeding, liver failure, shockDeferoxamine
IsoniazidTuberculosis (TB) medicationSeizures, severe metabolic acidosis, comaPyridoxine (vitamin B6)
InsulinDiabetes medicationSevere hypoglycemia, seizures, brain damageGlucose (dextrose)
IbuprofenOver-the-counter NSAID painkillerStomach bleeding, kidney damage, drowsinessNone specific; activated charcoal, supportive care
Ibotenic AcidFly Agaric (Amanita muscaria) mushroomConfusion, hallucinations, muscle twitchingNone specific; supportive care
IvermectinAntiparasitic medicationDizziness, tremors, coma at high dosesNone specific; supportive care
Isopropyl AlcoholRubbing alcohol, hand sanitizersDrowsiness, low blood pressure, stomach irritationNone specific; supportive care, dialysis
ImidaclopridNeonicotinoid insecticide, flea treatmentsNausea, tremors, breathing difficultyNone specific; supportive care
IndoxacarbAgricultural and household insecticideWeakness, methemoglobinemia, breathing troubleMethylene blue
IodineAntiseptic, industrial chemical, water purification tabletsCorrosive burns, thyroid dysfunction, breathing troubleSodium thiosulfate
Iris (Rhizome)Iris plant roots and bulbsVomiting, drooling, skin irritationNone specific; supportive care
Ipomoea SeedsMorning glory plant seedsHallucinations, nausea, dizzinessNone specific; supportive care
Indian TobaccoLobelia inflata plantVomiting, tremors, breathing depressionNone specific; supportive care
Irukandji VenomIrukandji jellyfish stingExcruciating pain, severe hypertension, heart strainNone specific; supportive care
IbogaineIboga shrub root barkHallucinations, irregular heartbeat, seizuresNone specific; cardiac monitoring
IpecacIpecacuanha syrupPersistent vomiting, muscle weakness, heart damageNone specific; supportive care
IndomethacinPrescription NSAIDStomach ulcers, kidney injury, confusionNone specific; supportive care
IsofluraneGeneral anesthetic gasBreathing depression, low blood pressure, arrhythmiaNone specific; supportive care

Descriptions

Iron (Ferrous Sulfate)
Iron overdose, often from swallowed supplement pills, damages the gut lining and overwhelms the liver; it’s one of the most common accidental poisonings in young children.
Isoniazid
This TB drug turns dangerous in overdose by blocking a brain enzyme, triggering relentless seizures that standard anti-seizure medicines often can’t stop without vitamin B6.
Insulin
Too much insulin drives blood sugar dangerously low, starving the brain of fuel; it has sadly been used as a deliberate poisoning agent because it’s hard to detect.
Ibuprofen
A household staple that’s generally safe, but massive overdoses can cause serious kidney injury, stomach ulcers, and in rare cases seizures or coma.
Ibotenic Acid
Found in the iconic red-and-white toadstool, this compound converts in the body to muscimol, producing dreamlike intoxication, nausea, and disorientation.
Ivermectin
Safe at prescribed veterinary and human doses, but large overdoses can cross into the brain and cause serious neurological symptoms, especially in sensitive animal breeds.
Isopropyl Alcohol
Swallowing rubbing alcohol produces a deeper, longer-lasting intoxication than drinking alcohol and can dangerously depress breathing and heart function.
Imidacloprid
One of the world’s most widely used insecticides, it disrupts insect nerve signals; large exposures in pets or people can cause vomiting and lethargy.
Indoxacarb
This crop and ant-bait insecticide interferes with nerve and blood cell function; accidental ingestion can turn blood an abnormal brownish color.
Iodine
Useful as a disinfectant in small doses, concentrated iodine burns tissue on contact and disrupts thyroid hormone balance if swallowed in quantity.
Iris (Rhizome)
The showy Iris flower hides a mildly toxic rhizome that causes stomach upset and mouth irritation in pets and people who chew on it.
Ipomoea Seeds
Certain morning glory varieties produce seeds containing LSD-like compounds; eating them recreationally can trigger unpredictable hallucinations and severe nausea.
Indian Tobacco
Despite its folk-medicine history as an emetic, this wildflower contains nicotine-like alkaloids that can dangerously depress breathing in larger amounts.
Irukandji Venom
Delivered by a thumbnail-sized jellyfish off northern Australia, this venom causes Irukandji syndrome, agonizing pain and a dangerous surge in blood pressure that can strain the heart.
Ibogaine
Used in West African ritual and as an experimental addiction treatment, this plant alkaloid can trigger visions but also dangerous heart rhythm disturbances.
Ipecac
Once a home remedy to induce vomiting after poisoning, repeated misuse of ipecac syrup can itself poison the heart and skeletal muscles.
Indomethacin
A potent anti-inflammatory drug that, in overdose, is harder on the stomach and kidneys than typical NSAIDs and can cause headaches and confusion.
Isoflurane
This inhaled surgical anesthetic is safe under medical supervision, but uncontrolled exposure can dangerously suppress breathing and heart rhythm.
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