After surgery, mu receptors are upregulated, increasing the effectiveness of opioids for pain control. Which statement is true?

• A. Mu receptors are upregulated, increasing the effectiveness of opioids for pain control.
• B. Mu receptors are downregulated, reducing the effectiveness of opioids.
• C. Mu receptors are unchanged, producing no change in opioid efficacy.
• D. Mu receptors become desensitized, leading to tolerance.

Answer: (A)

Upregulation means more mu opioid receptors are available or they respond more strongly to the same amount of drug. With more receptors, opioids can produce a stronger analgesic signal at a given dose, so pain control improves. That’s why this statement is true. If receptors were downregulated or became desensitized, the opposite would happen—efficacy would decrease or tolerance would develop. If receptor numbers were unchanged, there would be no change in opioid effectiveness.