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In physiology, tolerance occurs when an organism builds up a resistance to the effects of a substance after repeated exposure. This can occur with environmental substances such as salt or pesticides. It is also commonly encountered in pharmacology (see drug tolerance), when a subject's reaction to a drug (such as a painkiller or intoxicant) decreases so that larger doses are required to achieve the same effect.
There are two major mechanisms for tolerance:
- Dispositional tolerance: occurs because of a decreased quantity of the substance reaching the site it affects.
- Reduced responsiveness: the response to the substance is decreased by cellular mechanisms.[1]
References
- ^ Klaassen, Curtis D. (2001-07-27). Casarett & Doull's Toxicology: The Basic Science of Poisons, 6th, McGraw-Hill Professional, 17. ISBN 0071347216.
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