What is meant by drug tolerance?

This question is in my biology textbook for IGCSE and I have no idea what drug tolerance is. It would be very helpful if someone could clarify. Thank you.

  • 1
    $\begingroup$ Have you read the article in the Wikipedia about it? en.wikipedia.org/wiki/Drug_tolerance Do you have specific questions about it? $\endgroup$
    – Chris
    Sep 8 '14 at 8:20
  • $\begingroup$ Yes I did but I still couldn't get a clear picture of it in my head. $\endgroup$ Sep 8 '14 at 8:26
  • $\begingroup$ Would you happen to know another site with a clearer definition? $\endgroup$ Sep 8 '14 at 8:28
  • $\begingroup$ Can you tell us what you find unclear in this definition? This makes writing a meaningful answer easier. $\endgroup$
    – Chris
    Sep 8 '14 at 8:30
  • $\begingroup$ "when a subject's reaction to a specific drug and concentration of the drug is progressively reduced, requiring an increase in concentration to achieve the desired effect." $\endgroup$ Sep 8 '14 at 8:31

It basically means, that the body gets used to certain drugs and that you need to raise the dose to reach an effect. This is for example true for a number of anesthetics or pain medications as morphine.

Permanent application leads to a down-regulation of the drug receptor (for morphin this is the mu-opiod receptor) and the activation of counteracting signaltransduction pathways. To still get an activation you will need a higher drug concentration. For more details have a look at these articles:


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