Which term describes an undesirable occurrence related to the administration of a drug?

The term that describes an undesirable occurrence related to the administration of a drug is "adverse drug event." This term encompasses any harm that results from the use of a medication, which can include allergic reactions, side effects, or errors in prescribing, administering, or taking the drug. It is a broad category that captures various negative outcomes associated with drug therapy, regardless of whether they were preventable or not.

In contrast, an adverse drug interaction refers specifically to the negative effects that can occur when two or more drugs react with each other, which is a subset of what might be captured by an adverse drug event. Drug tolerance relates to a decrease in the effectiveness of a drug as a result of continued use, while drug classification refers to the categorization of drugs based on their properties or effects—neither of which addresses the concept of undesirable occurrences directly. Thus, the correct choice is the more comprehensive term that includes all kinds of undesired effects resulting from drug administration.