## Core Concept
The question tests understanding of opioid withdrawal symptoms, specifically those associated with heroin, a type of opioid. Heroin acts on opioid receptors in the brain, and its withdrawal leads to a variety of physical and psychological symptoms. The opioid withdrawal syndrome is characterized by symptoms that can be divided into two phases: early and late.

## Why the Correct Answer is Right
The correct answer, . Diarrhea, is a symptom commonly associated with opioid withdrawal. Symptoms of opioid withdrawal include anxiety, restlessness, insomnia, yawning, sweating, lacrimation, rhinorrhea, diarrhea, and muscle aches.

## Why Each Wrong Option is Incorrect
* **Option A:** . This option is incorrect because mydriasis (pupil dilation) is indeed a symptom of opioid withdrawal.
* **Option B:** . This option is incorrect because nausea and vomiting are also symptoms of opioid withdrawal.
* **Option D:** . This option is incorrect because hypertension is a symptom that can occur during opioid withdrawal due to the body's stress response.

## Clinical Pearl / High-Yield Fact
A key point to remember is that opioid withdrawal symptoms can be managed with medications like methadone and buprenorphine, which are used in the treatment of opioid use disorder.

## Correct Answer: .