Tolerance and Physical Dependency


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In order to really understand chronic opiate therapy and why it is a legitimate treatment, you need to know how to distinguish opiate use for pain from opiate use for addiction.  It can be confusing for both health professionals as well as lay people. 
That is because addiction is often confused with tolerance and physical dependency.  Addiction is talked about elsewhere but in order to understand that subject, one needs to have a clear understanding of the meanings of tolerance and physical dependency.


Drug tolerance is a state of adaptation in which exposure to a drug over time results in a diminution of one or more of the drug’s effects (euphoria, pain relief, anxiety relief).  Some examples are as follows: Vicodin no longer gives me the pain relief I used to get.  He can tolerate a dose of alcohol that will kill you or me.  Hytrin (a blood pressure drug) does not make me as lightheaded as it once did.  My Nitro patch is not as effective at relieving my chest pain as it once did.  Tolerance is a physiologic phenomenon that occurs with many drugs in many settings.  It will develop to all opiate medication if the medication is used with any degree of regularity.


A crucial concept in order to understand how people get into trouble involves the understanding that the brain is composed of many different areas.  Each area may develop tolerance at a different rate.  They will develop tolerance to the euphoria they get from a pain pill before they develop tolerance to it pain relieving effect.   Tolerance to nausea occurs over a different time frame.  Tolerance to fatigue occurs over yet another time frame   People almost never develop tolerance to the small pupils caused by opiates. 

Physical dependency refers to the occurrence of drug specific withdrawal symptoms.  It  almost always includes tolerance.  These withdrawal symptoms are different from those caused by the original disease process.  Examples are: Neurontin used for pain may cause seizures if stopped suddenly.  Catapres, used for blood pressure control, may cause a rebound increase in blood pressure if stopped suddenly.  This rebound is far greater than the original blood pressure abnormality.  Opiate and sedative discontinuations cause other symptoms.


The take home point is that these phenomena are physiologic consequences to ongoing exposure to the drug.  They represent adaptations at a cellular level.  They do not signify addiction.  A pain patient on 120 mgs. of MsContin  daily may be tolerant and physically dependent.  However, if he is working, supporting his family and happy with his life, he is not addicted.



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