Which statement best differentiates an adverse drug event (ADE) from a medication error?

• A. An ADE is harm caused by a drug during normal use; a medication error is a preventable mistake in the medication-use process.
• B. ADE is always unpredictable; medication errors are never harmful.
• C. Medication errors are about drug efficacy; ADEs are about dosing schedules.
• D. ADEs occur only with prescribed drugs; medication errors occur only with over-the-counter meds.

Answer: (A)

Adverse drug events happen when harm occurs from a drug used under normal conditions. This includes predictable side effects or toxicity, as well as reactions that occur even when the drug is used correctly and there isn’t a mistake in how it’s prescribed or given. A medication error, on the other hand, is about a preventable mistake in the medication-use process—things like giving the wrong dose, wrong drug, wrong patient, or administering without proper monitoring. The key difference is harm that arises from the drug itself during proper use versus a preventable lapse in the system that could lead to harm.

So the statement that best differentiates them is that an ADE is harm caused by a drug during normal use, while a medication error is a preventable mistake in the medication-use process. The other ideas—claiming ADEs are always unpredictable, or that errors can never be harmful, or that ADEs only relate to prescribed drugs versus errors with over-the-counter meds—don’t fit the real distinction between harm from drug exposure and preventable process mistakes.