What is an adverse drug reaction (ADR)?

An adverse drug reaction (ADR) is defined as an unintended harmful response to a medication when it is administered at normal doses. This definition underscores that ADRs can occur even when a drug is used as directed, making it crucial for healthcare professionals to monitor patients for any signs of such reactions. Recognizing that these reactions can happen at therapeutic doses helps in ensuring patient safety and in managing potential risks associated with medication use.

While the other choices describe various responses to medications, they don't capture the essence of what constitutes an ADR. For instance, a positive response to a medication indicates effectiveness rather than harm, and expected side effects are typically anticipated and documented in clinical trials, distinguishing them from ADRs which are unexpected. Lastly, a reaction occurring only after overdose does not align with the definition of ADRs, which can happen at standard dosages.