**Core Concept**
Sensitization to a drug refers to the process by which a person becomes more responsive to a particular substance, often due to changes in the nervous system or immune system. This phenomenon can lead to a heightened reaction to the drug, resulting in increased efficacy or adverse effects.

**Why the Correct Answer is Right**
Sensitization can occur through various mechanisms, including the development of tolerance to the drug's effects, changes in the expression or function of drug receptors, or alterations in the activity of enzymes involved in drug metabolism. For example, in the case of opioids, sensitization can lead to a condition known as opioid-induced hyperalgesia, where the individual becomes more sensitive to painful stimuli.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it describes tolerance, which is the opposite of sensitization. Tolerance occurs when a person requires an increased dose of a drug to achieve the same effect.

**Option B:** This option is incorrect because it describes a type of drug interaction, where the effect of one drug is enhanced by another. While this can occur, it is not the same as sensitization to a single drug.

**Option C:** This option is incorrect because it describes a type of drug resistance, where a person's body becomes less responsive to a particular drug. This is the opposite of sensitization.

**Option D:** This option is incorrect because it describes a type of pharmacokinetic change, where the body's ability to metabolize a drug is affected. While this can influence the efficacy of a drug, it is not the same as sensitization.

**Clinical Pearl / High-Yield Fact**
Sensitization to a drug can have significant clinical implications, including increased risk of adverse effects and altered treatment outcomes. It is essential for healthcare providers to recognize and manage sensitization to optimize patient care.

**Correct Answer:** C.