What is a proprietary drug?

A proprietary drug is one that is sold under a trademarked name and is typically available without the need for a prescription. This type of drug is often marketed by the company that holds the trademark and may be a brand-name formulation of a medication. It is important to note that proprietary drugs can include over-the-counter medications, which do not require a prescription for purchase.

The other options describe aspects that do not define proprietary drugs. For example, while controlled substances refer to medications regulated by law due to their potential for abuse, they can be either prescription or over-the-counter. Drugs sold only in hospitals pertain to a specific distribution channel, and those that must be purchased from a pharmacy suggest a necessity for retail setting purchases, which does not define the term proprietary itself. Hence, the understanding of proprietary drugs centers around their availability and branding, making the correct answer relevant and clear.