**Core Concept**
Cotton fever, also known as "cotton lung" or "cotton fever syndrome," is a condition associated with the intravenous injection of illicit substances, particularly heroin. It occurs due to the introduction of cotton fibers or other contaminants into the bloodstream through the injection site.

**Why the Correct Answer is Right**
The correct answer is B. Heroin, as it is the primary substance linked to cotton fever. When heroin is injected intravenously, the cotton fibers from the filter or the cotton balls used to prepare the solution are inadvertently introduced into the bloodstream. These fibers can cause an inflammatory response, leading to symptoms such as fever, chills, and respiratory issues. The pathophysiology involves the immune system reacting to the foreign particles, resulting in the release of pro-inflammatory cytokines and the activation of immune cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Amphetamine is a central nervous system stimulant and is not typically associated with cotton fever.
**Option C:** Phencyclidine (PCP) is a dissociative anesthetic and has a different set of risks and complications, including psychosis and hallucinations.
**Option D:** Cocaine is a powerful stimulant, but it is not commonly linked to cotton fever.

**Clinical Pearl / High-Yield Fact**
It's essential for healthcare professionals to be aware of the risks associated with intravenous substance abuse, including the introduction of contaminants like cotton fibers. A thorough history and physical examination are crucial in identifying patients at risk for cotton fever.

**✓ Correct Answer: B. Heroin**