Which of the following describes a side effect?

The correct answer focuses on a side effect as something that is typically unintended and not the primary purpose of administering a medication. A side effect specifically refers to any additional effect that occurs when a medication is used as prescribed, which highlights that side effects can occur alongside the therapeutic effect of the medication.

When considering the options, an immediate allergic reaction, while potentially serious, is categorized as an adverse reaction rather than a side effect. Drug interactions can lead to effects that may be unintended, but these are distinct from side effects linked specifically to an individual medication taken as directed. A medication overdose typically results in harmful or toxic effects rather than the side effects that are commonly anticipated when a drug is taken according to its established dosing guidelines.

In summary, the framing of side effects relates more closely to the unanticipated effects that can occur from the normal dosage of a medication, which is what makes it distinct from other types of reactions or conditions that medications may cause.