A patient with chronic back pain has been taking oral morphine sulfate for the past 2 years.Upon admission to the hospital,the patient receives morphine sulfate for back pain but reports no pain relief.The nurse notifies the health care provider,recognizing that the reason for the lack of pain relief is which of the following?

A) Side effect of the morphine
B) Drug dependence
C) Idiosyncratic response to the morphine
D) Medication tolerance

Medication tolerance is a decreased physiological response that occurs after repeated administration of a medication.Side effects are predictable and often unavoidable secondary effects produced at a usual therapeutic drug dose.Drug dependence can be physical or psychological.In psychological dependence,patients have an emotional desire for a drug to maintain an effect.A person believes that a desirable effect will result when taking the medication.Physical dependence is a physiological adaptation to a medication that manifests itself by intense physical disturbance when the medication is withdrawn.Medications often cause unpredictable effects,such as an idiosyncratic reaction,in which a patient overreacts or underreacts to a medication or has a reaction that is different from normal.