An individual with opioid use disorder requires increasingly larger doses to achieve the same analgesic effect. Which mechanism explains why opioid tolerance develops within the reward circuitry?

💡 Explanation

Opioid tolerance develops because repeated opioid exposure causes receptor downregulation in the nucleus accumbens, diminishing the brain's response to the drug. Therefore, more opioid is needed to activate the reward circuit, rather than changes in liver enzymes, endorphin synthesis, or GABAergic activity.

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