According to regulations, what defines a drug?

The definition of a drug according to regulations focuses on its intended use in diagnosis, treatment, or prevention of disease. The correct answer highlights that any article intended for use in disease diagnosis or treatment meets the criteria established under the Federal Food, Drug, and Cosmetic Act (FDCA). This legislation is fundamental in determining what constitutes a drug within the United States and emphasizes the importance of intent behind the use of a product.

The option mentioning aesthetic purposes does not align with the regulatory definition, as it covers substances not intended for medical use. Similarly, the option regarding products regulated exclusively by state law does not fit because the definition of a drug is rooted in federal regulations, which take precedence and apply universally across states. Finally, simply being an ingredient in over-the-counter products does not automatically classify something as a drug; it is the individual product's intended use that determines its classification. Therefore, the focus on intended use in medical contexts is what makes the selected definition the most accurate and relevant.