Which of the following best describes an adverse reaction to medication?

An adverse reaction to medication is characterized as a harmful or unintended effect that occurs when a drug is administered. This definition emphasizes the negative consequences that can arise, distinguishing adverse reactions from beneficial effects, which are the intended outcomes of a medication. In addition, while expected side effects are known potential responses that may occur and are often communicated to patients prior to administration, adverse reactions are not anticipated and can cause significant health risks.

Transient effects, which resolve quickly, typically do not fall into the category of adverse reactions unless they cause harm. Thus, option B accurately captures the essence of what constitutes an adverse reaction in the context of medication administration. Understanding this distinction is crucial for anyone involved in medication management, as it helps in monitoring and ensuring patient safety.