What is an adverse drug reaction?

An adverse drug reaction is defined as an unwanted or harmful reaction that occurs in response to a medication. This can manifest in various ways, ranging from mild side effects, like nausea or headaches, to more severe effects that could potentially lead to complications or require medical intervention. The key aspect of an adverse drug reaction is that it is not the intended therapeutic effect of the medication; instead, it represents an unexpected negative outcome following drug administration. Recognizing and understanding these reactions is crucial for healthcare providers to ensure patient safety and to make informed decisions regarding medication management.

The other options do not capture the true definition of an adverse drug reaction. A desired effect implies a beneficial outcome, which contrasts with the "adverse" nature. Similarly, while a delayed reaction can occur, it does not define the overarching concept of an adverse drug reaction itself. Finally, stating that a reaction does not require medical attention misrepresents the seriousness that some adverse drug reactions can pose, as they often necessitate prompt medical evaluation or intervention to mitigate risks.