Which of the following describes a drug according to the Health and Safety Code?

The correct answer describes a drug as a substance that affects the structure or function of the body. This definition aligns with the Health and Safety Code, which emphasizes the relationship between substances and their physiological impact on individuals. Drugs are primarily recognized for their ability to alter biochemical processes, which can either lead to therapeutic effects or potential harm, depending on their use.

The other choices focus on specific aspects that do not encompass the broader definition of what constitutes a drug. For instance, while a substance intended solely for recreational use may indeed be a drug, this description is limited and does not highlight the fundamental pharmacological characteristics of substances. Similarly, a device used in medical procedures refers to instruments rather than substances having direct biochemical effects. Lastly, a non-prescription item sold in stores may include common household products that do not necessarily qualify as drugs in the medical or pharmacological context. Thus, the broad, inclusive definition of a drug in terms of its effect on the body accurately captures the essence of the term.