Naltrexone is used to maintain abstinence following opioid withdrawal in addicts. It blocks all of the following features of opioid use, except:
**Core Concept**
Naltrexone is an opioid receptor antagonist used to prevent relapse in individuals with opioid use disorder. It works by blocking the mu-opioid receptors in the brain, which are responsible for the euphoric effects of opioids.
**Why the Correct Answer is Right**
Naltrexone blocks the euphoric effects of opioids by competitively inhibiting the binding of endogenous opioids to mu-opioid receptors. This prevents the release of dopamine in the nucleus accumbens, which is responsible for the rewarding effects of opioids. Additionally, naltrexone blocks the analgesic effects of opioids by preventing the activation of mu-opioid receptors in the spinal cord and brainstem.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because naltrexone does indeed block the euphoric effects of opioids, which is a key component of opioid use disorder.
**Option B:** Incorrect because naltrexone also blocks the analgesic effects of opioids, which is a common reason for opioid use.
**Option C:** Incorrect because naltrexone does prevent the development of physical dependence and tolerance to opioids, as it blocks the opioid receptors that are responsible for these effects.
**Clinical Pearl / High-Yield Fact**
It's worth noting that naltrexone is most effective when used in conjunction with counseling and behavioral therapy, as it can help to prevent relapse by blocking the euphoric effects of opioids and reducing the desire to use them.
**Correct Answer:** D.
(Note: The options A, B, C were not provided, so I assumed they were meant to be the incorrect options.)