Opioid tolerance types

The development of physical dependence is an invariable accompaniment of tolerance to repeated administration of an opioid of the - type. Failure to continue administering the drug results in a characteristic withdrawal or abstinence syndrome that reflects an exaggerated rebound from the acute pharmacologic effects of the opioid. 

Regarding drugs of abuse, tissue tolerance commonly occurs to the opioids, ethanol, and the sedatives of the benzodiazepine type. Tolerance does not develop to all drugs of abuse, however. Thus cocaine and the amphetamines maintain their stimulant and euphoriant effects for a prolonged period of administration without any need to increase the dose appreciably. 

Tolerance may result from a compensatory biochemical cell response to continued exposure to opioid. In short, both physical dependence and tolerance may follow the operation of homeostatic adaptation to continued high occupancy of opioid receptors. Changes of similar type may occur with GABA transmission, involving benzodiazepines. 

The other three types of tolerance (pharmacokinetic, pharmacodynamic, and learned) are clubbed as acquired tolerance. In contrast to innate tolerance, this type of tolerance develops with continued opioid administration, and thus represents true tolerance rather than genetically mediated lack of sensitivity to opioids. 

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