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EU standard toxic symbol, as defined by Directive 67/548/EEC.

In the context of biology, poisons are substances that can cause damage, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism. Legally and in hazardous chemical labelling, poisons are especially toxic substances; less toxic substances are labelled "harmful", "irritant", or not labelled at all.

In medicine (particularly veterinary) and in zoology, a poison is often distinguished from a toxin and a venom. Toxins are poisons produced via some biological function in nature, and venoms are usually defined as biologic toxins that are injected by a bite or sting to cause their effect, while other poisons are generally defined as substances which are absorbed through epithelial linings such as the skin or gut.


Some poisons are also toxins, usually referring to naturally produced substances, such as the bacterial proteins that cause tetanus and botulism. A distinction between the two terms is not always observed, even among scientists.

Animal toxins that are delivered subcutaneously (e.g. by sting or bite) are also called venom. In normal usage, a poisonous organism is one that is harmful to consume, but a venomous organism uses poison to defend itself while still alive. A single organism can be both venomous and poisonous.

The derivative forms "toxic" and "poisonous" are synonymous.

Within chemistry and physics, a poison is a substance that obstructs or inhibits a reaction, for example by binding to a catalyst. For example, see nuclear poison.

Paracelsus, the father of toxicology, once wrote: "Everything is poison, there is poison in everything. Only the dose makes a thing not a poison." The phrase "poison" is often used colloquially to describe any harmful substance, particularly corrosive substances, carcinogens, mutagens, teratogens and harmful pollutants, and to exaggerate the dangers of chemicals. The legal definition of "poison" is stricter. A medical condition of poisoning can also be caused by substances that are not legally required to carry the label "poison".

Uses of poison

Poisons are usually not used for their toxicity, but may be used for their other properties. The property of toxicity itself has limited applications: mainly for controlling pests and weeds, and for preserving building materials and food stuffs. Where possible, specific agents which are less poisonous to humans have come to be preferred, but exceptions such as phosphine continue in use.

Throughout human history, intentional application of poison has been used as a method of assassination, murder, suicide and execution. As a method of execution, poison has been ingested, as the ancient Athenians did (see Socrates), inhaled, as with carbon monoxide or hydrogen cyanide (see gas chamber), or injected (see lethal injection). Many languages describe lethal injection with their corresponding words for "poison shot". Poison was also employed in gunpowder warfare. For example, the 14th century Chinese text of the Huo Long Jing written by Jiao Yu outlined the use of a poisonous gunpowder mixture to fill cast iron grenade bombs.

"Poisoning of Queen Bona" by Jan Matejko

Poisonous materials are often used for their chemical or physical properties other than being poisonous. The most effective, easiest, safest, or cheapest option for use in a chemical synthesis may be a poisonous material. Particularly in experimental laboratory syntheses a specific reactivity is used, despite the toxicity of the reagent. Chromic acid is an example of such a "simple to use" reagent. Many technical applications call for some specific physical properties; a toxic substance may possess these properties and therefore be superior. Reactivity, in particular, is important. Hydrogen fluoride (HF), for example, is poisonous and extremely corrosive. However, it has a high affinity ( free energy) for silicon, which is exploited by using HF to etch glass or to manufacture silicon semiconductor chips.

Biological poisoning

Acute poisoning is exposure to a poison on one occasion or during a short period of time. Symptoms develop in close relation to the exposure. Absorption of a poison is necessary for systemic poisoning. In contrast, substances that destroy tissue but do not absorb, such as lye, are classified as corrosives rather than poisons.

Chronic poisoning is long-term repeated or continuous exposure to a poison where symptoms do not occur immediately or after each exposure. The patient gradually becomes ill, or becomes ill after a long latent period. Chronic poisoning most commonly occurs following exposure to poisons that bioaccumulate such as mercury and lead.

Contact or absorption of poisons can cause rapid death or impairment. Agents that act on the nervous system can paralyze in seconds or less, and include both biologically derived neurotoxins and so-called nerve gases, which may be synthesized for warfare or industry.

Inhaled or ingested cyanide as used as method of execution on US gas chambers almost instantly starves the body of energy by inhibiting the enzymes in mitochondria that make ATP. Intravenous injection of an unnaturally high concentration of potassium chloride, such as in the execution of prisoners in parts of the United States, quickly stops the heart by eliminating the cell potential necessary for muscle contraction.

Most (but not all) biocides, including pesticides, are created to act as poisons to target organisms, although acute or less observable chronic poisoning can also occur in non-target organism, including the humans who apply the biocides and other beneficial organisms. For example, the herbicide 2,4-D imitates the action of a plant hormone, to the effect that the lethal toxicity is specific to plants. Indeed, 2,4-D is not a poison, but classified as "harmful" (EU).

Many substances regarded as poisons are toxic only indirectly, by toxication. An example is "wood alcohol" or methanol, which is not poisonous itself, but is chemically converted to toxic formaldehyde and formic acid in the liver. Many drug molecules are made toxic in the liver, and the genetic variability of certain liver enzymes makes the toxicity of many compounds differ between individuals.

The study of the symptoms, mechanisms, treatment and diagnosis of biological poisoning is known as toxicology.

Exposure to radioactive substances can produce radiation poisoning, an unrelated phenomenon.

Poisoning management

  • Poison Control Centers (In the US reachable at 1-800-222-1222 at all hours) provide immediate, free, and expert treatment advice and assistance over the telephone in case of suspected exposure to poisons or toxic substances.

Initial medical management

  • Initial management for all poisonings includes ensuring adequate cardiopulmonary function and providing treatment for any symptoms such as seizures, shock, and pain.


  • If the toxin was recently ingested, absorption of the substance may be able to be decreased through gastric decontamination. This may be achieved using activated charcoal, gastric lavage, whole bowel irrigation, or nasogastric aspiration. Routine use of emetics (syrup of Ipecac) and cathartics are no longer recommended.
    • Activated charcoal is the treatment of choice to prevent absorption of the poison. It is usually administered when the patient is in the emergency room. However, charcoal is ineffective against metals, Na, K, alcohols, glycols, acids, and alkalis.
    • Whole bowel irrigation cleanses the bowel, this is achieved by giving the patient large amounts of a polyethylene glycol solution. The osmotically balanced polyethylene glycol solution is not absorbed into the body, having the effect of flushing out the entire gastrointestinal tract. Its major uses are following ingestion of sustained release drugs, toxins that are not absorbed by activated charcoal (i.e. lithium, iron), and for the removal of ingested packets of drugs (body packing/smuggling).
    • Gastric lavage, commonly known as a stomach pump, is the insertion of a tube into the stomach, followed by administration of water or saline down the tube. The liquid is then removed along with the contents of the stomach. Lavage has been used for many years as a common treatment for poisoned patients. However, a recent review of the procedure in poisonings suggests no benefit. It is still sometimes used if it can be performed within 1 h of ingestion and the exposure is potentially life threatening.
    • Nasogastric aspiration involves the placement of a tube via the nose down into the stomach, the stomach contents are then removed via suction. This procedure is mainly used for liquid ingestions where activated charcoal is ineffective, i.e. ethylene glycol.
    • Emesis (i.e. induced by ipecac) is no longer recommended in poisoning situations.
    • Cathartics were postulated to decrease absorption by increasing the expulsion of the poison from the gastrointestinal tract. There are two types of cathartics used in poisoned patients; saline cathartics (sodium sulfate, magnesium citrate, magnesium sulfate) and saccharide cathartics ( sorbitol). They do not appear to improve patient outcome and are no longer recommended.


Some poisons have specific antidotes:

Poison/Drug Antidote
paracetamol (acetaminophen) N-acetylcysteine
vitamin K anticoagulants, e.g. warfarin vitamin K
opioids naloxone
iron (and other heavy metals) desferrioxamine, Deferasirox or Deferiprone
benzodiazepines flumazenil
ethylene glycol ethanol, fomepizole or Thiamine
methanol ethanol or fomepizole
cyanide amyl nitrite, sodium nitrite & sodium thiosulfate
Organophosphates Atropine & Pralidoxime
Magnesium Calcium Gluconate
Calcium Channel Blockers ( Verapamil, Diltiazem) Calcium Gluconate
Beta-Blockers ( Propranolol, Sotalol) Calcium Gluconate and/or Glucagon
Isoniazid Pyridoxine
Atropine Phisostigmin

Enhanced excretion

  • In some situations elimination of the poison can be enhanced using diuresis, hemodialysis, hemoperfusion, peritoneal dialysis, or exchange transfusion.

Further treatment

  • In the majority of poisonings the mainstay of management is providing supportive care for the patient, i.e. treating the symptoms rather than the poison.

Types of poisons

The majority of this section is sorted by ICD-10 code, which classifies poisons based upon the nature of the poison itself. However, it is also possible to classify poisons based upon the effect the poison has (for example, "Metabolic poisons" such as Antimycin, Malonate, and 2,4-Dinitrophenol act by adversely disrupting the normal metabolism of an organism.)

(T36-T50) Poisoning by drugs, medicaments and biological substances

( T 36) Poisoning by systemic antibiotics

( T 37) Poisoning by other systemic anti-infectives and antiparasitics

( T 38) Poisoning by hormones and their synthetic substitutes and antagonists, not elsewhere classified

( T 39) Poisoning by nonopiod analgesics, antipyretics and antirheumatics

( T 40) Poisoning by narcotics and psychodysleptics ( hallucinogens)

( T 41) Poisoning by anaesthetics and therapeutic gases

( T 42) Poisoning by antiepileptic, sedative-hypnotic and antiparkinsonism drugs

( T 43) Poisoning by psychotropic drugs, not elsewhere classified

( T 44) Poisoning by drugs primarily affecting the autonomic nervous system Neurotoxins interfere with nervous system functions and often lead to near-instant paralysis followed by rapid death. They include most spider and snake venoms, as well as many modern chemical weapons. One class of toxins of interest to neurochemical researchers are the various cone snail toxins known as conotoxins.

  • Atropine
  • Poison hemlock

Anticholinesterases (T44.0)

  • Fasciculin
  • Nerve agents

Acetylcholine antagonists

  • Curare
  • Pancuronium

Cell membrane disrupters Others

  • Nicotine - not strictly a neurotoxin, but capable in large doses of causing heart attack

( T 45) Poisoning by primarily systemic and haematological agents, not elsewhere classified

  • Phytohaemagglutinin ( Red kidney bean poisoning)

( T 46) Poisoning by agents primarily affecting the cardiovascular system

  • Digitoxin
  • Digoxin
  • Ouabain

( T 47) Poisoning by agents primarily affecting the gastrointestinal system

  • Solanine
  • Hyoscyamine

( T 48) Poisoning by agents primarily acting on smooth and skeletal muscles and the respiratory system

  • Strychnine
  • Aconite

( T 49) Poisoning by topical agents primarily affecting skin and mucous membrane and by ophthalmological, otorhinolaryngological and dental drugs

( T 50) Poisoning by diuretics and other unspecified drugs, medicaments and biological substances

(T51-T65) Toxic effects of substances chiefly nonmedicinal as to source

( T 51) Toxic effect of alcohol

( T 52) Toxic effect of organic solvents

( T 53) Toxic effect of halogen derivatives of aliphatic and aromatic hydrocarbons

( T 54) Toxic effect of corrosive substances Corrosives mechanically damage biological systems on contact. Both the sensation and injury caused by contact with a corrosive resembles a burn injury.

  • Acids and bases, corrosives
    • Various light metal oxides, hydroxides, superoxides
    • Bleach, some pool chemicals, other hypochlorates (acidic and oxydizing effect)
    • Hydrofluoric acid

Acids (T54.2) Strong inorganic acids, such as concentrated sulfuric acid, nitric acid or hydrochloric acid, destroy any biological tissue with which they come in contact within seconds.

Bases (T54.3) Strong inorganic bases, such as lye, gradually dissolve skin on contact but can cause serious damage to eyes or mucous membranes much more rapidly. Ammonia is a far weaker base than lye, but has the distinction of being a gas and thus may more easily come into contact with the sensitive mucous membranes of the respiratory system. Quicklime, which has household uses, is a particularly common cause of poisoning. Some of the light metals, if handled carelessly, can not only cause thermal burns, but also produce very strongly basic solutions in sweat.

( T 55) Toxic effect of soaps and detergents

( T 56) Toxic effect of metals A common trait shared by toxic metals is the chronic nature of their toxicity (a notable exception would be bismuth, which is considered entirely non-toxic). Low levels of toxic metal salts ingested over time accumulate in the body until toxic levels are reached. Toxic metals are often inaccurately referred to as " heavy metals", although not all heavy metals are necessarily harmful and not all toxic metals are heavy metals.

Toxic metals are generally far more toxic when ingested in the form of soluble salts than in elemental form. For example, metallic mercury passes through the human digestive tract without interaction and is commonly used in dental fillings—even though mercury salts and inhaled mercury vapor are highly toxic.


( T 57) Toxic effect of other inorganic substances

  • (T57.0) Arsenic (see arsenic poisoning)
    • Arsenic compounds
      • Arsenic trioxide
      • Fowler's solution

Reducing agents

  • (T57.1) The most notable substance in this class is phosphorus.

( T 58) Toxic effect of carbon monoxide

  • (T58) By far the most notable metabolic poison is carbon monoxide, which blocks the ability of red blood cells to transport oxygen.

( T 59) Toxic effect of other gases, fumes and vapours

  • Formaldehyde (T59.2)
  • Phosgene
  • Phosphine
  • Hydrogen sulfide

Oxidizers Poisons of this class are generally not very harmful to higher life forms such as humans (for whom the outer layer of cells are more or less disposable), but lethal to microorganisms such as bacteria. Typical examples are ozone and chlorine (T59.4), either of which is added to nearly every municipal water supply in order to kill any harmful microorganisms present.

All halogens are strong oxidizing agents, fluorine (T59.5) being the strongest of all.

See also: Free radical

( T 60) Toxic effect of pesticides

  • Pesticide poisoning
  • Fluoroacetate is a metabolic poison that blocks a vital step in the citric acid cycle.
  • Rotenone is a metabolic poison that disrupts electron transport in cellular respiration.

( T 61) Toxic effect of noxious substances eaten as seafood

  • Ciguatera poisoning
  • Scombroid poisoning
  • Shellfish toxins (PSP, DSP, NSP, ASP )
  • Domoic acid (or Amnesic shellfish poisoning, ASP)
  • Tetrodotoxin

( T 62) Toxic effect of other noxious substances eaten as food

  • Food poisoning
  • Botulin toxin
  • Hemlock water dropwort
  • Grayanotoxin (Honey intoxication)
  • Tetanospasmin (Tetanos Toxin)

( T 63) Toxic effect of venomous animals

( T 64) Toxic effect of aflatoxin and other mycotoxin food contaminants

  • Fungal toxins
    • Amanita toxin, see Amanita phalloides
    • Muscarine
    • Aflatoxins

( T 65) Toxic effect of other and unspecified substances

  • (T65.0) Cyanide is a metabolic poison that bonds with an enzyme involved in ATP production.
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