## Core Concept
Naltrexone is an opioid receptor antagonist used primarily in the management of alcohol dependence and opioid dependence. It works by blocking the effects of opioids at their receptor sites. This action is crucial in understanding its therapeutic applications.

## Why the Correct Answer is Right
Naltrexone is specifically used for the treatment of alcohol dependence and opioid dependence. By blocking opioid receptors, naltrexone reduces the reinforcing effects of opioids and alcohol, thereby decreasing the desire to consume them. This mechanism is key to its role in managing substance use disorders.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because while naltrexone has applications in managing substance use disorders, option A is not specified. However, based on common knowledge, naltrexone is not primarily used for treating conditions like depression or anxiety disorders.
- **Option B:** This option is incorrect as it is not detailed, but generally, naltrexone's use is more specific than a broad category like "pain management" or similar, where opioids or other analgesics are typically considered.
- **Option C:** Without specifics, it's hard to directly refute, but given naltrexone's mechanism, it's clear that it's not used for conditions that would be treated by enhancing opioid effects.

## Clinical Pearl / High-Yield Fact
A key point to remember is that naltrexone can precipitate withdrawal in individuals physically dependent on opioids. Therefore, it's essential to ensure that patients are completely detoxified before starting naltrexone. This is a critical consideration in clinical practice to avoid inducing acute withdrawal.

## Correct Answer: D. Treatment of alcohol dependence.