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.
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.
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".
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's lethal effect can be combined with its allegedly magical powers; an example is the Chinese gu poison. 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.
On the whole, however, 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, cleaning and maintenance, 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 and many household chemicals continue in use.
Most poisonous materials still in use are used for their chemical or physical properties other than being poisonous. Many over-the-counter medications, such as aspirin and Tylenol, are quite toxic if ingested in sufficiently large quantities. Even alcohol can become toxic if too much is ingested in a short enough time. In laboratory environments, where specific chemical properties are often required, the most effective, easiest, safest, or cheapest option for use in a chemical synthesis may be a poisonous material. If a toxic substance possesses these properties more exactly than a non-toxic one, the toxic substance is superior. Chromic acid is an example of such a "simple to use" reagent, but reactivity, in particular, is important. Hydrogen fluoride (HF), for example, is both 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.
On the other hand, certain medical treatments actually make deliberate use of the toxicity of certain substances. Antibiotics (originally harvested from organisms but now artificially produced in laboratories) are highly disruptive to the biochemistry of micro-organisms while having almost no direct effect upon humans. Similarly, the drugs used in chemotherapy are quite toxic; the reason chemotheraputic drugs have far more severe side effects than antibiotics is that their toxicity is not as narrowly tailored. Their benefit arises from the fact that they are—hopefully—more toxic to cancerous cells than normal ones. Such substances could be classified as poisons under the categories defined above, as they are generally artificial in nature, but are not generally discussed as such.
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.
|vitamin K anticoagulants, e.g. warfarin||vitamin K|
|iron (and other heavy metals)||desferrioxamine, Deferasirox or Deferiprone|
|ethylene glycol||ethanol, fomepizole or Thiamine|
|methanol||ethanol or fomepizole|
|cyanide||amyl nitrite, sodium nitrite & sodium thiosulfate|
|Organophosphates||Atropine & Pralidoxime|
|Calcium Channel Blockers (Verapamil, Diltiazem)||Calcium Gluconate|
|Beta-Blockers (Propranolol, Sotalol)||Calcium Gluconate and/or Glucagon|