Any substance (natural or synthetic) that, at a certain dosage, damages living tissues and injures or kills. Poisons spontaneously produced by living organisms are often called toxins, venoms if produced by animals. Poisons may be ingested, inhaled, injected, or absorbed through the skin. They do not always have an all-or-none effect; degrees of poisoning may occur, and at a given dose some substances are far more toxic than others (e.g., a pinch of potassium cyanide can kill, whereas a single dose of ordinary table salt must be massive to kill). Poisoning may be acute (a single dose does significant damage) or chronic (repeated or continuous doses produce an eventual effect, as with chemical carcinogens).
The effects produced by poisons may be local (hives, blisters, inflammation) or systemic (hemorrhage, convulsions, vomiting, diarrhea, clouding of the senses, paralysis, respiratory or cardiac arrest). Agricultural pesticides are often poisonous to humans. Some industrial chemicals can be very toxic or carcinogenic. Most therapeutic drugs and health-care products can be poisons if taken inappropriately or in excess. Most forms of radiation can be toxic (&see; radiation injury). &Seealso; antidote; arsenic poisoning; fish poisoning; food poisoning; lead poisoning; medicinal poisoning; mercury poisoning; mushroom poisoning.
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