What is defined as a drug interaction?

A drug interaction is specifically defined as the situation where one drug influences the effect, whether positive or negative, of another drug. This influence can either enhance the efficacy of the other drug or increase its toxicity, which could lead to harmful effects. For example, if two medications are taken together, one medication may increase or decrease the absorption of the other, leading to unexpected therapeutic outcomes or adverse reactions.

In this context, defining drug interaction as the effect one drug has on the efficacy or toxicity of another captures the essence of how medications can influence each other within the body. The other options presented describe different concepts related to medications. Incorrect prescribing does not necessarily imply an interaction; it simply indicates an issue with the prescribing process. A side effect pertains to unintended effects of a single medication rather than how it interacts with another. Lastly, while the combined effect of two or more medications can occur, it doesn’t encompass the interaction aspect that is concerned with the interplay between specific drugs.