 |
| Hypothetical graph illustrating tolerance. Due to physiological changes in the body, increased doses of opioids are necessary to produce desired effects after a period of regular opioid use. Adapted from Way et al., 1969. |
| After some period of regular oppioid use, a person
requires elevated dosages to produce to same physiological effect.
This is known as tolerance. Tolerance extends to most of the effects
of opioids, including analgesia, euphoria and respiratory depression (Rang
et al., 1995). Therefore, the longer a heroin addict uses the drug, the
more heroin he needs to produce the desired "rush." Similarly, a
cancer patient who regularly uses morphine pain relievers needs to constantly
increase dosage to reduce pain.
Two mechanisms for tolerance have been proposed, metabolic and neurochemical mechanisms. In metabolic tolerance, the body becomes more efficient at breaking down chemicals that are over-represented. During the development of neurochemical tolerance, a realignment in |
the nervous system reduces the effect of an over-represented
chemical. For example, if the limbic system is frequently overactivated
with opioids, the number of opiate receptors in that region will decline
(Leonard, 1992).
Tolerance leads to a dependency, both physical and psychological, on opioids. After the development of neurochemical tolerance, opioids are necessary to produce a normal level of pleasure. Absence of the opioids brings about depression. Withdrawal symptoms that resemble a severe case of the flu are characteristic of a person attempting to quite opioid use after tolerance has been developed. A fear of withdrawal symptoms often causes a psychological dependency, which is characterized by cravings for the drugs (Rang et al., 1995). |
|
| Hypothetical graph illustrating tolerance. Due to physiological changes in the body, increased doses of opioids are necessary to produce desired effects after a period of regular opioid use. Adapted from Way et al., 1969. |
Animal Physiology HOT TOPICS |
This site was created during the fall semester of 1999 by Wes
Self,
a student at
Davidson College, as part of an assignment in Biology 312 (Animal Physiology). Questions, comments and suggestions are appreciated at weself@davidson.edu |