Tolerance & Sensitization

Repeated drug administration sometimes produces differences in the magnitude of effect produced by the repeated administrations. When effects become weaker over repeated drug administration, tolerance is said to develop to the drug effect. When effects become stronger over repeated drug administration, sensitization is said to develop to the drug. Such changes in responsiveness to a drug can be produced by pharmacokinetic changes, learning effects, and neuroadaptive responses. Of these three processes the latter two are actually inseparable--learning effects involve CNS changes and neuroadaptive effects can be considered a type of cellular learning. The applied label reflects the relative emphasis and not mediation by independent processes.


Sensitization (reverse tolerance)

Physical Dependence & Withdrawal Reactions

Withdrawal reactions (and physical dependence) are traditionally associated with tolerance, although more recent data suggest than can also be associated with sensitization.

Copyright 1999 Michael A. Bozarth
This page was last updated 04 November 1999 11:11 EDT
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