**Core Concept**
The volume of distribution (Vd) is a pharmacokinetic parameter that represents the ratio of the total amount of a drug in the body to its plasma concentration. It is an indicator of the drug's distribution between plasma and tissues.

**Why the Correct Answer is Right**
The correct answer is the factor that does not increase the volume of distribution of a drug. Generally, factors that increase the volume of distribution include:

* Lipid solubility: Drugs that are highly lipid-soluble tend to distribute more into tissues, increasing their Vd.
* Protein binding: Drugs that are highly bound to plasma proteins tend to have a lower free fraction in the bloodstream, increasing their Vd.
* High molecular weight: Drugs with a high molecular weight tend to remain in the bloodstream and have a lower Vd.
* High water solubility: Drugs that are highly water-soluble tend to remain in the bloodstream and have a lower Vd.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because [insert reason here]. For example, a highly lipid-soluble drug would increase the volume of distribution.
* **Option B:** This option is incorrect because [insert reason here]. For example, a drug with high protein binding would increase the volume of distribution.
* **Option C:** This option is incorrect because [insert reason here]. For example, a drug with a high molecular weight would decrease the volume of distribution.
* **Option D:** This option is incorrect because [insert reason here]. For example, a highly water-soluble drug would decrease the volume of distribution.

**Clinical Pearl / High-Yield Fact**
A high volume of distribution indicates that a drug is highly lipophilic and tends to distribute into tissues. This can be a desirable property for drugs that need to reach specific tissues, but it can also lead to increased toxicity if not carefully managed.

**Correct Answer:** C. High molecular weight.