In the context of biology, poisons are substances that cause injury, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale. Some poisons are also toxins, and a distinction between the two terms is not always observed, even among scientists. The derivative forms "toxic" and "poisonous" are synonomous. Within chemistry and physics, a poison is a substance that obstructs or inhibits a reaction, for example by binding to a catalyst.

Table of contents
1 Biological poisoning
2 Famous poisonings
3 Poisons in crime fiction

Biological poisoning

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 almost instantly starves the body of energy by poisoning mitochondria and the synthesis of 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. Such rapid reactions are often called acute poisoning.

A poison may also act slowly. This is known as chronic poisoning and is most common for poisons that bioaccumulate. Examples of these types of poisons are mercury, lead, and asbestos.

Many substances regarded as poisons are toxic only indirectly. An example is "wood alcohol" or methanol, which is not poisonous itself, but is chemically converted to toxic formaldehyde 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 one individual and the next.

Milkweeds (Asclepias sp.) produce glycosides which are toxic to most organisms. (It is unlikely that any organism will eat much because of the extremely bitter taste.) Monarch butterfly larvae, however, are not susceptible to the toxin; in fact they accumulate it in their bodies as they eat the leaves of their host plant. Any predator who wishes to make a meal of an adult monarch will tend to be dissuaded by the bitter taste, and learn to leave the brightly colored insects alone. This gives considerable protection for monarchs from birds and other predators.

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.

Examples of biological poisons

Non-radioactive inorganic poisons

Organic poisons Naturally produced posions and toxins

Famous poisonings

Poisons in crime fiction

This is of course an inexhaustive list. You may wish to add other novels and/or specify the poisons used.


Films: See Also venom --toxicity -- Antidote -- Mithridates VI of Pontus -- Pollutant -- Lethal injection --Toxicity rating -- biosecurity -- Lead poisoning--skull and crossbones.

Poison is also the name of a US rock band active in the 1980s and 1990s. For more information, see Poison.