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Tolerance:
Tolerance:
A condition characterized by a reduced effect of a drug upon repeated administration. In some cases, it may be necessary to increase the dose of the drug to attain the same effect, or the original level of effect may be unattainable. Tolerance typically develops over days to weeks, and is distinguished from tachyphylaxis, a more rapid decline in the effect of a drug. Tolerance can result from multiple mechanisms, including changes in drug metabolism and alteration in the number or responsiveness of receptors (see desensitization). "Tolerance" should not be used to mean "lack of sensitivity" manifested toward a single dose of a drug. A non-habitual drinker who is unaffected by several drinks of whisky downed in rapid succession is probably insensitive to alcohol rather than tolerant to its effects.
Cf. Addiction, Sensitivity, Habituation, Dependence
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